Applied Science, Faculty of
Engineering, School of (Okanagan)
DSpace
UBCO
Doja, Somi
Doctor of Philosophy - PhD
University of British Columbia
An indispensable component of many land-based transportation systems are tires. Tires are composed of materials resistant to both physical and chemical changes and do not readily degrade naturally in the environment. Particularly, mining tires are designed to operate in harsh environments and hence are highly resistant to degradation. However, despite their omnipresence, the recycling of mining tires has not been thoroughly researched, and without suitable end-of-life solutions, discarded mining tires pose dire ecological and economical challenges. In this research, chemical and heat treatment methods were employed to study the upgrading of carbon black obtained from a tire recycling operation. Chemical treatment was employed to remove inorganic impurities present in the char, while a heat treatment was required for the removal of volatiles (for example sulphur) which could not be removed by chemical treatments. Acids including HCl, HNO₃, H₂SO₄ were successful in removing Zn, Fe, and other metallic impurities, whereas NaOH and KOH were used to remove Si. Heat treatment experiments under N₂ proved to be successful in S removal. A combination of chemical treatment (5M HCl and 10M NaOH leaching), along with thermal treatment (950°C), was ideal for removing most impurities from the recovered carbon black (rCB) yielding a purity of >98 wt%. Activation experiments were performed on purified rCB using KOH and CO2. Activated carbon obtained from KOH treatment exhibited the highest surface area of 994 m²/g. Purified and activated rCB was tested for Li-ion battery applications. The activated rCB anode showed a maximum discharge capacity of 1853 mAh/g. However, the capacity drop for activated rCB cells was greater than 40% after the first cycle of charge, likely due to the formation of solid electrolyte interface and irreversible side reactions. In addition, rCB was also used as an additive material in lithium titanate oxide (LTO) battery anodes. rCB proved to be a stable additive to LTO anode with negligible irreversible capacity loss (<10%). Electrochemical testing of cells made with LTO electrodes revealed that activated rCB additives had better discharge capacity values compared to Super-P additive. Hence this study demonstrated that mining tire-derived rCB could be used as an additive material for commercial Li-ion battery applications.
Upgrading of recycled carbon forenergy storage applicationsbySomi DojaMASc, University of British Columbia, 2017B.Tech., Jamia Millia Islamia, 2015A THESIS SUBMITTED IN PARTIAL FULFILLMENT OFTHE REQUIREMENTS FOR THE DEGREE OFDOCTOR OF PHILOSOPHYinThe College of Graduate Studies(Mechanical Engineering)THE UNIVERSITY OF BRITISH COLUMBIA(Okanagan)June 2022© Somi Doja 2022The following individuals certify that they have read, and recommend to the College ofGraduate Studies for acceptance, a dissertation entitled:Upgrading of recycled carbon for energy storage applicationssubmitted by Somi Doja in partial fulfilment of the requirements of the degree ofDoctor of Philosophy.Dr. Lukas Bichler, School of EngineeringSupervisorDr. Jian Liu, School of EngineeringSupervisory Committee MemberDr. Alexander Uhl, School of EngineeringSupervisory Committee MemberDr. John Steen, University of British Columbia - VancouverUniversity ExaminerDr. Houshang Alamdari, University of LavalExternal ExamineriiAbstractAn indispensable component of many land-based transportation systems are tires. Tiresare composed of materials resistant to both physical and chemical changes and do notreadily degrade naturally in the environment. Particularly, mining tires are designed tooperate in harsh environments and hence are highly resistant to degradation. However,despite their omnipresence, the recycling of mining tires has not been thoroughlyresearched, and without suitable end-of-life solutions, discarded mining tires pose direecological and economical challenges.In this research, chemical and heat treatment methods were employed to study theupgrading of carbon black obtained from a tire recycling operation. Chemical treatment wasemployed to remove inorganic impurities present in the char, while a heat treatment wasrequired for the removal of volatiles (for example sulphur) which could not be removed bychemical treatments. Acids including HCl, HNO3, H2SO4 were successful in removing Zn,Fe, and other metallic impurities, whereas NaOH and KOH were used to remove Si. Heattreatment experiments under N2 proved to be successful in S removal. A combination ofchemical treatment (5M HCl and 10M NaOH leaching), along with thermal treatment(950°C), was ideal for removing most impurities from the recovered carbon black (rCB)yielding a purity of >98 wt%.Activation experiments were performed on purified rCB using KOH and CO2. Activatedcarbon obtained from KOH treatment exhibited the highest surface area of 994 m2/g. Purifiedand activated rCBwas tested for Li-ion battery applications. The activated rCB anode showeda maximum discharge capacity of 1853 mAh/g. However, the capacity drop for activatedrCB cells was greater than 40% after the first cycle of charge, likely due to the formationof solid electrolyte interface and irreversible side reactions. In addition, rCB was also usediiias an additive material in lithium titanate oxide (LTO) battery anodes. rCB proved to be astable additive to LTO anodewith negligible irreversible capacity loss (<10%). Electrochemicaltesting of cells made with LTO electrodes revealed that activated rCB additives had betterdischarge capacity values compared to Super-P additive. Hence this study demonstrated thatmining tire-derived rCB could be used as an additive material for commercial Li-ion batteryapplications.ivLay SummaryTires are a vital component of most transportation systems, and do not degradenaturally in the environment. Conventionally, waste tires are discarded in landfills, posingsevere ecological challenges. Carbon black (CB) is a major constituent of tires, and itsextraction can be beneficial for advanced applications, including energy storage. The mainobjective of this work was to recover carbon black (rCB) from waste tires. This rCB wasfurther purified by chemical and heat treatments to produce battery-grade carbon. Thepurified rCB was used to make button-sized lithium-ion batteries and its performance wasstudied. It was proven that some of these batteries performed better than the commerciallyavailable batteries made with Super-P CB. Thus, this work demonstrated a promisingmethod to recycle waste tires for use in the lithium battery industry.vPrefaceThis research thesis titled "Upgrading recycled carbon for energy storage applications"was written for the partial fulfillment of the Doctor of Philosophy (PhD) degree at theUniversity of British Columbia.The contents of the Literature Review chapter presented in this thesis have been publishedin parts in the following paper:• S. Doja, L.K. Pillari, L. Bichler, "Processing and activation of tire-derived char: A review",Renewable and Sustainable Energy Reviews, vol. 155, pp.111860, jan 2022"Part of the experimental work was performed at the German Aerospace Center locatedin Cologne, Germany. Modification of carbon materials was performed in the materialsprocessing laboratory under the supervision of Dr. Lukas Bichler at the University of BritishColumbia Okanagan. Battery fabrication and testing was performed in the battery researchgroup supervised by Dr. Jian Liu at the University of British Columbia Okanagan.viTable of ContentsAbstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iiiLay Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vPreface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . viTable of Contents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . viiList of Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xiiList of Figures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xviList of Equations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xxviList of Abbreviations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .xxviiList of Acronyms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .xxviiiAcknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xxixChapter 1: Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.1 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.2 Research objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31.3 Scope of research . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41.4 Thesis structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5viiTABLE OF CONTENTSChapter 2: Literature Review . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72.2 Commercial carbon black . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82.2.1 Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82.2.2 Production . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102.2.3 Physical properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102.3 EOL tires as precursors for CB production . . . . . . . . . . . . . . . . . . . . 112.3.1 Composition of tires . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112.3.2 Properties of rCB derived from tires . . . . . . . . . . . . . . . . . . . 122.4 Recycling end-of-life tires for CB production . . . . . . . . . . . . . . . . . . . 142.4.1 Pyrolysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 142.4.2 Demineralization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162.4.3 Activation of tire char . . . . . . . . . . . . . . . . . . . . . . . . . . . 172.5 Recovered CB (rCB) in battery systems . . . . . . . . . . . . . . . . . . . . . . 212.6 Li-ion batteries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 232.6.1 Cathodes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 252.6.2 Anodes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 252.6.3 Carbon conductive additives . . . . . . . . . . . . . . . . . . . . . . . . 282.7 Tire-derived rCB for Li-ion batteries . . . . . . . . . . . . . . . . . . . . . . . . 292.8 Summary of literature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32Chapter 3: Experimental Procedure . . . . . . . . . . . . . . . . . . . . . . . . . 353.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 353.2 Precursor materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 363.2.1 Raw carbon char . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 363.2.2 Super-P conductive carbon . . . . . . . . . . . . . . . . . . . . . . . . 373.3 Upgrading of raw carbon char for Li-ion batteries . . . . . . . . . . . . . . . . 383.3.1 Chemical treatment of raw carbon char . . . . . . . . . . . . . . . . . 38viiiTABLE OF CONTENTS3.3.2 Heat treatment of leached carbon black . . . . . . . . . . . . . . . . . 433.3.3 Activation of leached carbon black . . . . . . . . . . . . . . . . . . . . 443.4 Fabrication and testing of Li-ion cells . . . . . . . . . . . . . . . . . . . . . . . 453.4.1 rCB as additive in LTO batteries . . . . . . . . . . . . . . . . . . . . . . 463.4.2 rCB as active material in Li-ion batteries . . . . . . . . . . . . . . . . . 473.4.3 Electrochemical testing of Li-ion half cells . . . . . . . . . . . . . . . . 473.5 Material characterization techniques . . . . . . . . . . . . . . . . . . . . . . . 503.5.1 Skeletal density measurement . . . . . . . . . . . . . . . . . . . . . . . 503.5.2 Nitrogen adsorption . . . . . . . . . . . . . . . . . . . . . . . . . . . . 513.5.3 Elemental analysis by combustion . . . . . . . . . . . . . . . . . . . . 523.5.4 Electrical conductivity measurements . . . . . . . . . . . . . . . . . . 533.5.5 X-ray diffraction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 533.5.6 Scanning electron microscopy . . . . . . . . . . . . . . . . . . . . . . . 543.5.7 Transmission electron microscopy . . . . . . . . . . . . . . . . . . . . 543.5.8 FTIR analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 553.5.9 FTIR gas analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 563.5.10 Raman spectroscopy . . . . . . . . . . . . . . . . . . . . . . . . . . . . 563.5.11 Proximate analysis of rCB . . . . . . . . . . . . . . . . . . . . . . . . . 573.5.12 ICP-AES analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 583.6 Nomenclature of different carbon materials . . . . . . . . . . . . . . . . . . . . 59Chapter 4: Results and Discussion: Chemical Leaching . . . . . . . . . . . . . . 604.1 Acid leaching of raw carbon char . . . . . . . . . . . . . . . . . . . . . . . . . 604.1.1 Optimization of type of acid . . . . . . . . . . . . . . . . . . . . . . . . 604.1.2 Optimization of molarity of acid . . . . . . . . . . . . . . . . . . . . . 634.1.3 Optimization of slurry ratio . . . . . . . . . . . . . . . . . . . . . . . . 644.1.4 Optimization of leaching time . . . . . . . . . . . . . . . . . . . . . . . 664.2 Base leaching of raw carbon char . . . . . . . . . . . . . . . . . . . . . . . . . 67ixTABLE OF CONTENTS4.2.1 Optimization of type of base . . . . . . . . . . . . . . . . . . . . . . . . 684.2.2 Optimization of molarity of base . . . . . . . . . . . . . . . . . . . . . 704.2.3 Optimization of slurry ratio . . . . . . . . . . . . . . . . . . . . . . . . 714.2.4 Optimization of leaching time . . . . . . . . . . . . . . . . . . . . . . . 724.3 Combined acid and base leaching . . . . . . . . . . . . . . . . . . . . . . . . . 744.3.1 Physical analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 744.3.2 Chemical analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 784.4 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82Chapter 5: Results and Discussion: Activation and Devolatilization ofLeached CB . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 835.1 Activation of leached CB . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 835.1.1 Carbon dioxide activation . . . . . . . . . . . . . . . . . . . . . . . . . 835.1.2 Potassium hydroxide activation . . . . . . . . . . . . . . . . . . . . . . 895.2 Devolatilization of leached CB . . . . . . . . . . . . . . . . . . . . . . . . . . . 965.2.1 Effect of heat treatment temperature . . . . . . . . . . . . . . . . . . . 975.2.2 Effect of heat treatment time . . . . . . . . . . . . . . . . . . . . . . . 995.2.3 Effect of heating rate . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1015.2.4 Analysis of leached CB + heat sample . . . . . . . . . . . . . . . . . . 1035.3 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110Chapter 6: Results and Discussion: Electrochemical Testing . . . . . . . . . . . 1126.1 Effect of chemical treatment of raw carbon char on specific discharge capacity 1126.1.1 Chemically treated rCB as anode . . . . . . . . . . . . . . . . . . . . . 1126.1.2 Chemically treated rCB in LTO anodes . . . . . . . . . . . . . . . . . . 1186.2 Effect of heat treatment of rCB on specific discharge capacity of Li-ion batteries1226.2.1 Heat-treated rCB as anode . . . . . . . . . . . . . . . . . . . . . . . . . 1226.2.2 Heat-treated rCB in LTO anodes . . . . . . . . . . . . . . . . . . . . . 129xTABLE OF CONTENTS6.3 Effect of activation experiments of rCB on specific discharge capacity of Li-ionbatteries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1336.3.1 Activated rCB as anode . . . . . . . . . . . . . . . . . . . . . . . . . . 1336.3.2 Activated rCB as additive in LTO anodes . . . . . . . . . . . . . . . . . 1436.4 Mechanism of lithiation in rCB anode materials . . . . . . . . . . . . . . . . . 1496.5 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152Chapter 7: Conclusions and Future Work . . . . . . . . . . . . . . . . . . . . . . 1547.1 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1547.2 Research limitations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1577.3 Future work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 158Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159AppendicesAppendix A: Leaching Experiments . . . . . . . . . . . . . . . . . . . . . . . . . . 187Appendix B: Heat Treatment Experiments . . . . . . . . . . . . . . . . . . . . . . 194Appendix C: Electrochemical Experiments . . . . . . . . . . . . . . . . . . . . . . 196Appendix D: Analysis of 5M HCl and 10M NaOH Treated Raw Carbon Char . . 206Appendix E: Equipments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 208xiList of TablesTable 2.1 Summary of pyrolysis conditions for the treatment of waste tires forrecovering carbon black. . . . . . . . . . . . . . . . . . . . . . . . . . . . 15Table 2.2 Carbonization charateristics of EOL tires used for production of carbonfor Li-ion battery applications. . . . . . . . . . . . . . . . . . . . . . . . 30Table 3.1 Composition of raw carbon char from SEM-EDS analysis. . . . . . . . . 37Table 3.2 Summary of product numbers for chemicals used in this thesis. . . . . . 39Table 3.3 Summary of different chemical treatments performed in this thesis fora leaching time of 2 h and slurry ratio of 50 g/L. . . . . . . . . . . . . . . 40Table 3.4 Summary of different slurry ratios, molarities and leaching times usedin this thesis for HCl and NaOH leaching. . . . . . . . . . . . . . . . . . 40Table 3.5 Summary of heat treatment experiments performed in this thesis. . . . . 44Table 3.6 Summary of KOH activation experiments performed in this thesis. . . . 44Table 3.7 Different grades of rCB tested for electrochemical performance in LTOand C anode systems. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49Table 4.1 TGA proximate analysis results of acid treated raw carbon char. . . . . . 62Table 4.2 Skeletal density measurements of acid treated raw carbon char. . . . . . 63Table 4.3 TGA proximate analysis results of base treated raw carbon char. . . . . 69Table 4.4 Skeletal density measurements of base treated raw carbon char. . . . . . 70Table 4.5 TGA proximate analysis results of leached carbon black. . . . . . . . . . 78Table 4.6 Elemental analysis results of leached carbon black. . . . . . . . . . . . . 82xiiLIST OF TABLESTable 5.1 N2 adsorption results from CO2 activation of leached CB. . . . . . . . . . 86Table 5.2 Raman spectroscopy results for CO2AC (1000-3). . . . . . . . . . . . . . 89Table 5.3 N2 adsorption results from KOHAC samples. . . . . . . . . . . . . . . . . 92Table 5.4 Raman spectroscopy results for KOHAC (900-2-4). . . . . . . . . . . . . 96Table 5.5 TGA proximate analysis: Effect of heat treatment temperature ondevolatilization of leached carbon black. . . . . . . . . . . . . . . . . . . 99Table 5.6 TGA proximate analysis: Effect of heat treatment time ondevolatilization of leached carbon black. . . . . . . . . . . . . . . . . . . 101Table 5.7 Peak temperatures of DTA peaks during heating of rCB. . . . . . . . . . 103Table 5.8 TGA proximate analysis: Effect of heating rate on devolatilization ofleached carbon black. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103Table 5.9 TGA proximate analysis results of leached CB + heat sample. . . . . . . 105Table 5.10 Raman spectroscopy results for leached CB + heat sample. . . . . . . . . 110Table 6.1 Specific discharge capacity of chemically treated rCB anode cells afterdifferent cycles of charge and discharge. . . . . . . . . . . . . . . . . . . 114Table 6.2 Specific discharge capacity of chemically treated rCB anode cells after10 cycles for different C rates. . . . . . . . . . . . . . . . . . . . . . . . . 115Table 6.3 Electrochemical parameters obtained from curve fitting of EIS results. . 116Table 6.4 Specific discharge capacity of chemically treated rCB doped LTOanodes after different cycles of charge and discharge. . . . . . . . . . . . 120Table 6.5 Specific discharge capacity of chemically treated rCB doped LTO anodecells after 10 cycles for different C rates. . . . . . . . . . . . . . . . . . . 120Table 6.6 Electrochemical parameters obtained from curve fitting of EIS results. . 121Table 6.7 Specific discharge capacity drop after 1 cycle of charge and dischargefor heat-treated rCB anode. . . . . . . . . . . . . . . . . . . . . . . . . . 123Table 6.8 Specific discharge capacity of heat-treated rCB anode cells after 10cycles for different C rates. . . . . . . . . . . . . . . . . . . . . . . . . . . 125xiiiLIST OF TABLESTable 6.9 Electrochemical parameters for leached CB + heat anode obtained fromcurve fitting of EIS results. . . . . . . . . . . . . . . . . . . . . . . . . . . 129Table 6.10 Specific discharge capacity drop of heat-treated rCB doped LTO anodesafter different cycles of charge and discharge. . . . . . . . . . . . . . . . 130Table 6.11 Electrochemical parameters of heat-treated rCB doped LTO anodeobtained from curve fitting of EIS results. . . . . . . . . . . . . . . . . . 132Table 6.12 Specific discharge capacity of activated rCB anodes after different cyclesof charge and discharge. . . . . . . . . . . . . . . . . . . . . . . . . . . . 136Table 6.13 Specific discharge capacity of activated rCB anode cells after 10 cyclesfor different C rates. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137Table 6.14 Electrochemical parameters of activated rCB anodes obtained fromcurve fitting of EIS results. . . . . . . . . . . . . . . . . . . . . . . . . . . 140Table 6.15 Specific discharge capacity drop of activated rCB doped LTO anodesafter different cycles of charge and discharge. . . . . . . . . . . . . . . . 143Table 6.16 Specific discharge capacity of activated rCB doped LTO anodes after 10cycles for different C rates. . . . . . . . . . . . . . . . . . . . . . . . . . . 145Table A.1 Effect of type of acid used for leaching on purity of rCB (at 5 Mconcentration, 2 hours, slurry ration 50g/L) from SEM-EDS analysiswithout normalization. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 188Table A.2 Effect of type of acid used for leaching on purity of rCB (at 10 Mconcentration) from SEM-EDS analysis without normalization. . . . . . 188Table A.3 Effect of concentration of HCl used for leaching on purity of rCB fromSEM-EDS analysis without normalization. . . . . . . . . . . . . . . . . . 189Table A.4 Effect of slurry ratio used for HCl leaching on purity of rCB from SEM-EDS analysis without normalization (at 1M HCl for 24 hours). . . . . . . 189Table A.5 Effect of HCl leaching time on purity of rCB obtained from SEM-EDSanalysis without normalization. . . . . . . . . . . . . . . . . . . . . . . . 190xivLIST OF TABLESTable A.6 Effect of type of base used for leaching on purity of rCB from SEM-EDSanalysis without normalization. . . . . . . . . . . . . . . . . . . . . . . . 190Table A.7 Effect of concentration of NaOHused for leaching on purity of rCB fromSEM-EDS analysis without normalization. . . . . . . . . . . . . . . . . . 191Table A.8 Effect of slurry ratio used for NaOH leaching on purity of rCB fromSEM-EDS analysis without normalization (1M NaOH for 24 hrs). . . . . 191Table A.9 Effect of NaOH leaching time on purity of rCB from SEM-EDS analysiswithout normalization. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 192Table A.10 Repeated TGA proximate analysis results of base treatment on rawcarbon char. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 192Table A.11 Elemental analysis results of leached carbon black. . . . . . . . . . . . . 192Table B.1 Burnoff values from activation of leached CB. . . . . . . . . . . . . . . . 194Table B.2 Peak temperatures of three DTA peaks for different sample temperatureand holding times. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 194Table B.3 N2 adsorption results from non-activated CB samples. . . . . . . . . . . 195Table C.1 Electrochemical parameters of activated rCB doped LTO anodesobtained from curve fitting of EIS results. . . . . . . . . . . . . . . . . . 196xvList of FiguresFigure 1.1 Volumetric and gravimetric energy densities of various batterysystems (Figure 1 from B. Diouf and R. Pode, (2015). Potential oflithium-ion batteries in renewable energy, Renewable Energy, vol.76,©with permission from Elsevier). . . . . . . . . . . . . . . . . . . . . . 2Figure 1.2 Flowchart illustrating the scope of research. . . . . . . . . . . . . . . . 4Figure 2.1 Off-the-road mining tires on a Komatsu mining truck. . . . . . . . . . . 8Figure 2.2 Structure of commercial carbon black (Figure 1 fromE.M.Dannenberg,L. Paquin, and H. Gwinnell (2000). Carbon Black, Wiley books, ©withpermission from John Wiley & Sons Inc.) . . . . . . . . . . . . . . . . . 9Figure 2.3 Structural evolution and TEM images of carbon black with increasein heat treatment temperature showing: a) Amorphous carbon(Figure 5 from Z. Czigany and L. Hultman (2010). Interpretation ofelectron diffraction patterns from amorphous and fullerene-likecarbon allotropes, Ultramicroscopy, vol. 110, pp. 815–819, ©withpermission from Elsevier), b) Turbostratic carbon (Figure 5 from ©R.Gómez-Hernández, Y. Panecatl-Bernal, and M. Á. Méndez-Rojas(2019). High yield and simple one-step production of carbon blacknanoparticles from waste tires, Heliyon, vol. 5, published by ElsevierLtd) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13xviLIST OF FIGURESFigure 2.4 A comparison of charge and discharge curves for Na-ion batteries withtire-derived carbon anodes pyrolyzed at different temperatures (Figure3d from Y. Li, M. P. Paranthaman, K. Akato, A. K. Naskar, A. M. Levine,R. J. Lee, S.-O. Kim, J. Zhang, S. Dai, and A. Manthiram (2016). Tire-derived carbon composite anodes for sodium ion batteries, Journal ofPower Sources, vol. 316, pp. 232–238, ©with permission from ElsevierB.V. ). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23Figure 2.5 Li-ion battery construction (Figure 1.12 from L. Zhen, Sajid Bashir,Jingbo Louise (2019). Technology Policy and Road Map of Battery,Springer Nature, ©with permission from Springer-Verlag GmbHGermany, part of Springer Nature) . . . . . . . . . . . . . . . . . . . . . 24Figure 2.6 Use of carbon additives in Li-ion cathode. (Figure: Graphical abstractN. Kwon, D. Mouck-Makanda, and K. Fromm (2018). A Review:Carbon Additives in LiMnPO4- and LiCoO2-Based CathodeComposites for Lithium Ion Batteries, Batteries, vol. 4, p. 50). . . . . . . 29Figure 2.7 Cyclic performance of tire-derived rCB at 50 A/g for untreatedpyrolyzed char (UPC), acid treated char (CA) and KOH activated char(CK-n with ”n” specifying the impregnation ratio) (Figure 10 from R.Kumar and A. Sharma (2018). Morphologically tailored activatedcarbon derived from waste tires as high-performance anode forLi-ion battery, Journal of Applied Electrochemistry, vol. 48, pp. 1–13,©with permission from Springer Science Business Media B.V., part ofSpringer Nature) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31xviiLIST OF FIGURESFigure 2.8 Cycling performance of carbon (control tire rubber derived) anode at0.1C (Figure 7c from A. K. Naskar, Z. Bi, Y. Li, S. K. Akato, D. Saha, M.Chi, C. A. Bridges, and M. P. Paranthaman (2014). Tailored recoveryof carbons from waste tires for enhanced performance as anodes inlithium-ion batteries, RSC Advances, vol. 4, p. 38213,©with permissionfrom RSC advances). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32Figure 3.1 SEM (SE) image of raw carbon char used as precursor for all experiments. 36Figure 3.2 SEM (SE) image of Super-P® conductive carbon used in this research:a) At 200x, b) At 100Kx. . . . . . . . . . . . . . . . . . . . . . . . . . . 38Figure 3.3 Description of combined acid and base treatment for preparation ofleached CB from raw carbon char. . . . . . . . . . . . . . . . . . . . . . 41Figure 3.4 Pressure filtration system used for filtration of chemically treated rCBafter chemical leaching: a) Pressure filter, and b) Stainless steel meshassembly. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42Figure 3.5 Netzsch STA Jupiter F3 DTA/TG unit. . . . . . . . . . . . . . . . . . . . 43Figure 3.6 Fabrication of Li-ion half cell: a) Pestle and mortar, b) Doctor’s blade,c) Vacuum oven, and d) Punching station. . . . . . . . . . . . . . . . . . 46Figure 3.7 Modified Randle’s circuit: Equivalent circuit used for curve fitting ofEIS results. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48Figure 3.8 Electrochemical testing station for Li-ion half cells. . . . . . . . . . . . 50Figure 3.9 Nitrogen adsorption equipment: a) Degassing station, b)Micromeritics® Tristar Plus analyzer, and c) TGA analysis results forheating rCB sample from room temperature to 300 °C under flowingnitrogen (degassing conditions). . . . . . . . . . . . . . . . . . . . . . . 52Figure 3.10 Transmission Electron Microscope (TEM) at DLR. . . . . . . . . . . . . 55Figure 3.11 Netzsch Instruments® TGA/FTIR equipment. . . . . . . . . . . . . . . . 56xviiiLIST OF FIGURESFigure 3.12 Schematic of proximate analysis experiment performed in the TGAunit: a) Sample at room temperature (N2), b) Sample at 120 °Cindicating moisture loss (N2), c) Sample at 950°C indicating volatileremoval (N2), and d) Sample at 950°C indicating ash left (air) . . . . . . 58Figure 4.1 SEM-EDS analysis of impurities present in different grades of rCBobtained after acid treatment on raw carbon char . . . . . . . . . . . . 61Figure 4.2 Effect of acid concentration on purity of rCB: a) ICP analysis of acidsolutions obtained after leaching experiments were complete, and b)SEM-EDS analysis of different grades of rCB obtained. . . . . . . . . . 64Figure 4.3 Effect of acid slurry ratio (g/L) on purity of rCB: a) ICP analysis of acidsolutions obtained after leaching experiments were complete, and b)SEM-EDS analysis of different grades of rCB obtained. . . . . . . . . . 65Figure 4.4 Effect of acid leaching time on purity of rCB: a) ICP analysis of acidsolutions obtained after leaching experiments were complete, and b)SEM-EDS analysis of different grades of rCB obtained. . . . . . . . . . 67Figure 4.5 SEM-EDS analysis of impurities present in different grades of rCBobtained after base treatment of raw carbon char. . . . . . . . . . . . . 69Figure 4.6 Effect of base concentration on purity of rCB: a) ICP analysis of basesolutions obtained after leaching experiments were complete, and b)SEM-EDS analysis of different grades of rCB obtained. . . . . . . . . . 71Figure 4.7 Effect of base slurry ratio (g/L) on purity of rCB: a) ICP analysis of basesolutions obtained after leaching experiments were complete, and b)SEM-EDS analysis of different grades of rCB obtained. . . . . . . . . . 72Figure 4.8 Effect of base leaching time on purity of rCB: a) ICP analysis of basesolutions obtained after leaching experiments were complete, and b)SEM-EDS analysis of different grades of rCB obtained. . . . . . . . . . 73Figure 4.9 SEM (BSE) analysis of leached carbon black: a) At 200x, and b) At 500x. 75xixLIST OF FIGURESFigure 4.10 TEM images of: a) Raw CB, and b-d) Leached CB. . . . . . . . . . . . . 76Figure 4.11 Electrical analysis of rCB samples: a) Effect of applied pressure onelectrical conductivity, and b) Raman spectroscopy of rCB samples. . . 77Figure 4.12 TEM-EDS mapping results of raw CB: a) TEM image of analyzedarea, b) Layered image (C=red, ZnS=blue, SiC=yellow, SiO=green,unallocated=grey), c) Zn map, and d) S map. . . . . . . . . . . . . . . . 79Figure 4.13 Chemical analysis of leached and raw carbon char: a) XRD analysis,and b) FTIR spectroscopy of rCB. . . . . . . . . . . . . . . . . . . . . . 81Figure 5.1 SBET and Vmi of leached CB activated with CO2: a) Effect oftemperature, and b) Effect of time. . . . . . . . . . . . . . . . . . . . . . 84Figure 5.2 BET analysis of CO2 activated rCB: a) Adsorption isotherm, and b) Poresize distribution of CO2 activated samples. . . . . . . . . . . . . . . . . 85Figure 5.3 SEM images of the CO2AC (1000-3) sample: a) At 1kx, and b) At 15kx. . 87Figure 5.4 FTIR analysis of CO2AC (1000-3) sample. . . . . . . . . . . . . . . . . . 88Figure 5.5 Raman spectrocopy and curve fitting results for CO2AC (1000-3) sample. 89Figure 5.6 SBET and Vmi of leached CB activated with KOH: a) Effect oftemperature, b) Effect of time, and c) Effect of impregnation ratio. . . . 90Figure 5.7 BET analysis of KOH activated rCB: a) Adsorption isotherm, and b)Pore size distribution. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91Figure 5.8 SEM images of the KOHAC (900-2-4) sample: a) At 1 Kx, b) At 15Kx,and TEM images c) At low magnification, and d) At high magnification. 93Figure 5.9 Analysis of KOHAC (900-2-4) samples: a) Effect of applied pressure onelectrical conductivity, and b) FTIR analysis of rCB. . . . . . . . . . . . 95Figure 5.10 Raman spectroscopy results for KOHAC (900-2-4) sample. . . . . . . . 96Figure 5.11 Effect of heat treatment temperature on devolatilization of leached CB:FTIR gas analysis results a) At target temperature, and b) After 1h ofheating at target temperature. . . . . . . . . . . . . . . . . . . . . . . . 98xxLIST OF FIGURESFigure 5.12 Effect of heat treatment temperature on devolatilization of leached CBfrom TGA analysis. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99Figure 5.13 Effect of heat treatment time on devolatilization of leached CB: FTIR-gas analysis of leached CB heated for different holding times. . . . . . . 100Figure 5.14 Effect of heat treatment time on devolatilization of leached CB fromTGA analysis. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101Figure 5.15 Effect of heating rate on devolatilization of leached CB: FTIR-gasanalysis of leached CB heated for different heating rates. . . . . . . . . 102Figure 5.16 Effect of heating rate on devolatilization of leached CB from TGAanalysis. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102Figure 5.17 SEM images of leached CB + heat sample: a) At 200x, b) At 1kx, andTEM images a) At low magnification, and b) At high magnification. . . 104Figure 5.18 Heat treatment of leached CB: FTIR-gas analysis from volatileevolution: a) At temperature increments of 100 °C, b) TG-DTAanalysis, and FTIR-gas analysis at c) 600 °C, and d) 900 °C). . . . . . . . 106Figure 5.19 BET analysis of leached CB + heat sample: a) Adsorption isotherm, andb) Pore size distribution. . . . . . . . . . . . . . . . . . . . . . . . . . . 108Figure 5.20 FTIR analysis of leached CB + heat sample. . . . . . . . . . . . . . . . . 109Figure 5.21 Raman spectroscopy and curve fitting of leached CB + heat sample. . . 110Figure 6.1 Cycling of chemically treated rCB electrodes as anode at 0.5C: a)Specific discharge capacity with respect to cycle number, and b)Charge discharge curves. . . . . . . . . . . . . . . . . . . . . . . . . . . 114Figure 6.2 Effect of C rate on specific discharge capacity from chemically treatedrCB used as anode. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116Figure 6.3 EIS test results from chemically treated rCB used as anodes beforecycling experiments(Nyquist plot). . . . . . . . . . . . . . . . . . . . . . 117xxiLIST OF FIGURESFigure 6.4 Cycling of LTO + chemically treated rCB electrodes as anode at 0.5C:a) Specific discharge capacity with respect to cycle number, and b)Charge discharge curves. . . . . . . . . . . . . . . . . . . . . . . . . . . 119Figure 6.5 Effect of C rate on the specific discharge capacity of chemically treatedrCB doped LTO anodes. . . . . . . . . . . . . . . . . . . . . . . . . . . . 121Figure 6.6 EIS test results from chemically treated rCB doped LTO anodes beforecycling experiments (Nyquist plot). . . . . . . . . . . . . . . . . . . . . 122Figure 6.7 Cycling of heat-treated rCB anode at 0.5C: a) Specific dischargecapacity with respect to cycle number, and b) Charge discharge curves. 124Figure 6.8 Effect of C rate on the specific discharge capacity of heat-treated rCBanode. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125Figure 6.9 SEM images of leached CB + heat anode: a) Virgin, and after charge-discharge of: b) 1 cycle, c) 25 cycles, d) 50 cycles, and e) 100 cycles. . . . 126Figure 6.10 Discharge curves for the first three cycles of leached CB + heat anode. 127Figure 6.11 EIS test results from heat-treated rCB anode before cyclingexperiments (Nyquist plot). . . . . . . . . . . . . . . . . . . . . . . . . . 128Figure 6.12 Cycling of heat-treated rCB doped LTO anodes at 0.5C: a) Specificdischarge capacity with respect to cycle number, and b) Chargedischarge curves. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130Figure 6.13 EIS test results fromheat-treated rCB doped LTO anodes before cyclingexperiments (Nyquist plot). . . . . . . . . . . . . . . . . . . . . . . . . . 131Figure 6.14 Structure of heat-treated rCB doped LTO anode after 100 cycles ofcharging and discharging obtained from SEM analysis: a) At 500x,and b) At 5Kx. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133Figure 6.15 Cycling of activated rCB anode at 0.5C: a) Specific discharge capacitywith respect to cycle number, and b) Charge discharge curves. . . . . . 135xxiiLIST OF FIGURESFigure 6.16 Effect of C-rate on the specific discharge capacity of activated rCB usedas anode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137Figure 6.17 SEM images of KOHAC (900-2-4) anode: a) Virgin, and after 100 cyclesof charging and discharging at: b) 500x, c) 1kx, and d) 10Kx. . . . . . . 139Figure 6.18 EIS test results from activated rCB anodes before cycling experiments(Nyquist plot). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 140Figure 6.19 TGA mass loss results from heat treatment of activated rCB samplesheated to 900°C in N2 gas. . . . . . . . . . . . . . . . . . . . . . . . . . . 141Figure 6.20 Discharge curves for the first three cycles of KOHAC (900-2-4) anode. . 142Figure 6.21 Cycling of activated rCB doped LTO anodes at 0.5C: a) Specificdischarge capacity with respect to cycle number, and b) Chargedischarge curves. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 144Figure 6.22 Effect of C rate on the specific discharge capacity of activated rCBdoped LTO anode. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145Figure 6.23 EIS test results from activated rCB doped LTO anodes before cyclingexperiments (Nyquist plot). . . . . . . . . . . . . . . . . . . . . . . . . . 146Figure 6.24 Discharge curves for the first three cycles of CO2AC (1000-3) dopedLTO anode. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147Figure 6.25 EIS analysis of LTO+CO2AC (1000-3) cell before and after cyclingexperiments. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 148Figure 6.26 Structure of CO2AC (1000-3) doped LTO anode before cycling: a) At500x, b) At 10Kx, and after 100 cycles of charging and discharging: c)At 500x, and d) At 10Kx. . . . . . . . . . . . . . . . . . . . . . . . . . . 149Figure 6.27 Mechanism of lithiation in rCB anodes . . . . . . . . . . . . . . . . . . . 151Figure 6.28 Mechanism for Li-intercalation in rCB doped LTO anodes. . . . . . . . 152Figure A.1 Repeats from SEM-EDS analysis of raw carbon char. . . . . . . . . . . . 187xxiiiLIST OF FIGURESFigure A.2 SEM-EDS analysis of different grades of rCB obtained by modificationof NaOH concentration (without normalization). . . . . . . . . . . . . . 187Figure A.3 TEM-EDS mapping results of raw CB: a) C map, b) O map, c) Si map,d) Fe map, and e) Al map. . . . . . . . . . . . . . . . . . . . . . . . . . . 193Figure B.1 Raman spectroscopy repeats of Super-P. . . . . . . . . . . . . . . . . . . 195Figure C.1 TGA analysis of all rCB samples under N2 atmosphere. . . . . . . . . . 196Figure C.2 Structure of virgin rCB electrodes: a) and b) Leached CB, c) and d)Leached CB + heat. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 197Figure C.3 Structure of virgin rCB electrodes (continued): a) and b)KOHAC (900-2-4), c) and d) CO2AC (1000-3). . . . . . . . . . . . . . . . . . . . . . . . 198Figure C.4 Structure of rCB electrodes after 100 cycles of charging anddischarging: a) and b) Raw carbon char, c) and d) Leached CB. . . . . . 199Figure C.5 Structure of rCB electrodes after 100 cycles of charging anddischarging (continued): a) and b) Super-P, c) and d) CO2AC (1000-3). . 200Figure C.6 Structure of virgin LTO + rCB electrodes: a) and b) Leached CB, c) andd) Leached CB + heat. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 201Figure C.7 Structure of LTO + rCB electrodes after 100 cycles of charging anddischarging: a) and b) LTO+ KOH AC (900-2-4), c) and d) LTO + Super-P. 202Figure C.8 Charging curves for first few cycles of leached CB doped LTO anode. . 203Figure C.9 Curve fitting for rCB doped LTO anodes using Zsimpwin software: a)Raw carbon char, b) Leached CB, and c) Leached CB + heat. . . . . . . . 204Figure C.10 Curve fitting for rCB+LTO anodes using Zsimpwin software(continued): a) KOHAC (900-2-4), and b)CO2AC (1000-3). . . . . . . . . 205Figure D.1 TEM-imaging of 5 M HCl and 10 M NaOH. . . . . . . . . . . . . . . . . 206Figure D.2 XRD analysis of 5 M HCl and 10 M NaOH treated CB. . . . . . . . . . . 207Figure D.3 FTIR analysis of 5 M HCl and 10 M NaOH treated CB. . . . . . . . . . . 207Figure E.1 Equipments used for experiments: a) Fumehood, and b) Tube furnace. . 208xxivLIST OF FIGURESFigure E.2 Electrochemical testing details from neware software: a) C anodecycling, and b) LTO anode cycling. . . . . . . . . . . . . . . . . . . . . . 209Figure E.3 EIS analysis: a) BioLogic SAS Potentiostat, b) Electrochemical conditions. 210Figure E.4 Material characterization equipments: a) AccuPyc for skeletal densityanalysis, b) Bruker XRD analyzer, and c) Mettler Toledo microgram scale. 210Figure E.5 Screenshots from WiRE software for Raman Analysis: a) Extendedscan information, and b) Laser information. . . . . . . . . . . . . . . . . 211xxvList of Equations2.1 Reaction of ferrous sulphide with hydrochloric acid. . . . . . . . . . . . . . . . . . . . . . . . 162.2 Reaction of zinc sulphide with hydrochloric acid. . . . . . . . . . . . . . . . . . . . . . . . . . . 172.3 Reaction of sulphur with potassium hydroxide. . . . . . . . . . . . . . . . . . . . . . . . . . . . 172.4 Reaction of silica with sodium hydroxide. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 172.5 Reaction of carbon with steam. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 182.6 Reaction of carbon with carbon dioxide gas. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 182.7 Degradation of potassium carbonate during potassium hydroxide activation . . . . 192.8 Reaction of carbon with potassium hydroxide. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 192.9 Conversion reaction in a Li-ion cell. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 243.1 Calculation of resistivity from resistance. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 533.2 Relationship between microcrystalline planar crystal size and ID/IG. . . . . . . . . . . . 57xxviList of AbbreviationsAC Activated CarbonBET Brunauer-Emmett-TellerCB Carbon BlackDLR Deutsches Zentrum für Luft- und RaumfahrtDSC Differential Scanning CalorimetryEOL End-Of-LifeFTIR Fourier-Transform Infrared SpectroscopyIUPAC International Union of Pure and Applied ChemistryOTR Off-The-RoadPAH polycyclic aromatic hydrocarbonsrCB recovered Carbon BlackSBET BET Surface AreaSE Secondary ElectronSEI Solid Electrolyte InterfaceSEM Scanning Electron MicroscopeTEM Transmission Electron MicroscopeTGA Thermogravimetric AnalysisXRD X-Ray DiffractionX-EDS X-Ray Energy Dispersive SpectroscopyxxviiList of Acronyms2θ Angle between incident and refracted ray in Bragg’s lawλ Wavelengthρ DensityLa Crystallite sizeCs CapacitanceRs Electrolyte and electrode resistanceRSEI SEI layer resistanceRct Charge transfer resistanceW Warburg impedancexxviiiAcknowledgementsI would like to express my deepest gratitude to my supervisor Dr. Lukas Bichler for hisconstant support and guidance throughout the course of my Ph.D. program. I thank him foralways supporting my research ideas, which has helped me grow as a student and researchertremendously, and I owe it to him. I also thank you, for the all the help with writing thisthesis and the research papers. This endeavour would not have been possible without yoursupport.I am grateful to Dr. Jian Liu for his advice and recommendations for improving myresearch. Thank you for trusting me with your lab and giving access to all the equipment.Thanks should also go to my committee member Dr. Alexander Uhl for his excellentsuggestions on data interpretation, improving the quality of my work. I would like toexpress my sincere thanks to Dr. Marina Schwan and Dr. Barbara Milow for giving me theexciting opportunity to advance my research by performing additional experiments at theGerman Aerospace Center. Special thanks should also go to Mr. Peter Nilsson and Mr. ScottFarnham for their never ending support and expert advice on the industrial aspect of thiswork.I had the pleasure of working with extremely supporting colleagues: Dr. Anil Prasad, Dr.Kristian Mackowiak, Dr. Josh Stroh, Mr. Lava Kumar Pillari, Mr. Kyle Lessoway, and Mr.Sadhak Gautam. Thank you all for all your help during my Ph.D. journey. Thanks also toanyone I’ve forgotten who was instrumental in this project. Lastly, I’d like to recognize therelentless support from my parents Mr. M.N. Doja and Mrs. Shazi Doja, my brother FarazDoja, and my husband Mr. Aadil Khan Ghazi. I could not have finished this journey withoutmy family.xxixChapter 1: IntroductionThis chapter outlines the need for the research and development in the area of recycling wastetires to create value added products. Then, the framework for the objectives and motivation ofthe current research is presented along with a definition of the scope of this research.1.1. BackgroundGlobal warming continues to drive efforts to seek environmentally friendly alternativesfor energy generation. With increased awareness about environmental concerns of usingfossil fuels, there is increased attention to look for other sources of energy. Renewable energysources, like wind or solar, are possible options to generate energy, but face challenges on alarge scale for a constant supply of energy.An important component of future energy mix are rechargeable batteries. Figure 1.1shows the maximum energy that can be extracted from rechargeable lithium (Li)-ion batterysystems. Li remains an attractive candidate for battery materials due to its low weight andhigh energy storage capacity, especially for applications in portable electronic devices.However, their use in the automobile industry remains challenging due to the need forfrequent charging (as a result of their limited capacity). Also, the cost associated with thefabrication of batteries is high, contributing to the relatively higher cost of electric vehicles.Wood et al.[1] reported that the major cost associated with a Li-ion battery remains in theelectrode materials. Therefore, electrode materials have been closely scrutinized withrespect to their electrochemical performance, as well as economic and environmentalfactors. Of particular interest were identified carbon (C)-based materials and carbonadditives from diverse sources. In addition to naturally occurring carbon (e.g., coal orgraphite), the energy sector and Li-ion battery manufacturers in particular have been11.1. BACKGROUNDseeking new sources of carbon, especially via recycling and re-purposing streams. Thesecarbon materials generally have a high purity (>99%), a high electrical conductivity (>0.5S/cm) and low SBET values (<90 m2/g) [2]. In this respect, recycling of rubber products hasbeen identified as an opportunity with economic and environmental benefits.Figure 1.1: Volumetric and gravimetric energy densities of various battery systems (Figure1 from B. Diouf and R. Pode, (2015). Potential of lithium-ion batteries in renewable energy,Renewable Energy, vol.76, © with permission from Elsevier)[3].An indispensable component of any land-based transportation system are tires. Tires arecomposed of materials resistant to both physical and chemical changes and do not decomposenaturally in the environment. Conventionally, waste tires are dumped in landfills, or recycledfor low-cost applications [4–6]. Despite their omnipresence, recycling of used tires poses direecological and economical challenges. Based on available estimates, in North America andEurope alone, 5 M tonnes of tire waste was generated every year, which creates a majorrisk for human health, and environmental hazards (e.g. insect plagues, fires, and chemicalsleaching into underground water) and imposed an extreme demand on landfill space [6].Approximately a third of automotive and mining tires is carbon black (CB). Mining tiresdiffer in composition from an automobile tire predominantly in the amount of natural rubber.Natural rubber decomposes at lower temperature (320-400 ◦C) when compared to synthetic21.2. RESEARCH OBJECTIVESrubber (400-520 ◦C) [7]. There are numerous initiatives to recover (or reclaim) the CB fromtires [8]. Further literature suggests that it is easier to extract CB frommining tires (containingnatural rubber) when compared to automobile tires (synthetic rubber) [9]. It was predictedthat the need of CB will increase by 6 M tonnes from 2015 to 2022 with an annual growthrate of 5.6% [10]. Extraction and re-use of the recovered CB (rCB) can be beneficial for avariety of applications, such as plastics, paints, pigments, coatings, and possibly batteries [11].In Canada, it was reported that 50% of end-of-life (EOL) mining tires originate from BritishColumbia [12]. Yet, there was only one Canadian study about the possibility of recyclingof mining tires [12]. The use of rCB instead of commercially produced CB (typically froma petrochemical process) would reduce CO2 emissions by upto 84% [13]. This intensified animmediate need to pursue studies focusing on the recovery of CB from EOLmining tires. Dueto the ever concerning climatic changes globally, the need for sustainably sourced materialswill keep increasing.1.2. Research objectivesThe objectives for this research were driven by the opportunity to extract carbon-basedmaterials from recycled mining tires and to study the application of such materials for Li-ionbattery applications. The objectives of this thesis are listed as follows:1. To characterize raw carbon char originating from EOL mining tires recycled via apyrolysis process.2. To increase the purity of the as-received raw carbon char via chemical leaching andheat treatment process. The target was to reach a high level of purity of the recoveredcarbon black (>99%).3. To study the effect of activation on the structure and surface area of the recoveredcarbon black.31.3. SCOPE OF RESEARCH4. To study the effect of chemical, heat treatment and activation of recovered carbon blackon the performance of Li-ion half cells.5. To compare the performance of recovered carbon black as a substitute to graphite anodein Li-ion cells.6. To fabricate and test performance of recovered carbon black used as an additive in LTObattery anodes.1.3. Scope of researchTo achieve these objectives, the research was divided into three stages as shown in Figure 1.2.Figure 1.2: Flowchart illustrating the scope of research.1. Modification of raw carbon char: This involved chemical and heat treatment41.4. THESIS STRUCTUREexperiments on raw carbon char. There were two sub-parts in this stage. First, theeffect of different chemical treatments was investigated where the chemicalconcentration, leaching time, and raw carbon char to chemical ratio was studied.Second, the effect of the heat treatment and activation on the structure and purity ofleached carbon black was explored.2. Characterization: This stage of the research consisted of characterization of the rCBsamples. Characterization techniques such as EDS, SEM, XRD, TGA, TEM and Ramanspectroscopy were employed.3. Fabrication and electrochemical testing of Li-ion batteries: The analysis of allthe results from the first two parts enabled preparation of different grades of rCB. Theperformance of Li-ion half cells prepared with different grades of rCB was evaluated.1.4. Thesis structureThis thesis contains six chapters, excluding the introduction.Chapter 2: Literature Review- This chapter provides a concise summary of publishedliterature relevant to this thesis. It includes details on recycling of waste tires and thefundamentals of Li-ion battery systems.Chapter 3: Experimental Procedure- This chapter outlines the details of experiments,materials and methods used in this research.Chapter 4: Results and Discussion: Chemical Leaching- This chapter contains resultsfrom the chemical treatment experiments performed in this research. This chapter alsoprovides an elaborate discussion of these results.Chapter 5: Results and Discussion: Devolatilization and Activation- This chaptercontains results from the heat treatment and activation experiments performed in thisresearch, along with an in-depth discussion of the results.Chapter 6: Results and Discussion: Electrochemical Testing- This chapter presents51.4. THESIS STRUCTUREresults from the electrochemical testing of Li-ion cells made with different grades of rCBanodes produced in this research. This chapter also provides an elaborate discussion ofthese results.Chapter 7: Conclusions and Future Work- This chapter offers a concise summary of theresults generated in this work, along with recommendations for future work.6Chapter 2: Literature ReviewThis chapter provides an overview of selected literature pertinent to this study. This literaturereview is focused on information pertaining to the recycling end-of-life tires, and carbonmaterialsin Li-ion batteries.2.1. IntroductionLi-ion batteries have gained a wide popularity due to their low density to high power ratio[14]. Li metal is a good reducing agent and readily forms Li cations allowing easy movementof electrons. Carbon (C) is perhaps the most common anode material used in Li-ion batteries[15]. C is also used as a conductive additive to boost the performance of various electrodeactive materials in Li-ion battery systems.With the continuously increasing demand for energy storage materials, C (and graphite)has been identified as a critical supply material by the United States Geological Survey (USGS)[16]. As a result, there is a need to explore alternative precursors to produce carbonaceousmaterials. One such precursor is CB originating from EOL mining tires. Figure 2.1 shows aKomatsu mining truck with 73" diameter off-the-road (OTR) tires. Presently, commercial CBis used in Li-ion batteries as a conductive filler material. The following section provides adescription of production and properties of commercial CB materials.72.2. COMMERCIAL CARBON BLACKFigure 2.1: Off-the-road mining tires on a Komatsu mining truck.2.2. Commercial carbon black"Carbon black" is a generic term used to identify a low density C powder (C>92 wt%) [17,18]. CB is formed by thermal degradation of hydrocarbons in the absence of oxygen (O2) [19].The properties of CB can be controlled by varying the thermal degradation conditions (i.e.temperature, time, atmosphere) which make it different from soot (undesired C by-productformed from incomplete combustion of organic matter) [19]. CBs have a complex aggregatestructure different from that of other forms of carbon such as diamond, charcoal, or graphite.2.2.1. StructureFigure 2.2 shows a schematic of CB structure [17]. The term aggregate describes a discreterigid colloidal unit composed of spheres (primary particles) fused together. The size and shapeof these aggregates define the structure of the CB (high or low). When a large number of82.2. COMMERCIAL CARBON BLACKprimary particles coalesce in an aggregate, then a high structure CB forms whereas smalleraggregates form low structure CB materials [20]. Within the primary particle are micro-graphitic layers arranged together in random orientations. The distance between the micro-graphitic layers of CB is generally greater than in the case of graphite (>0.335 nm) as a result ofthe CB’s random planar orientation. The relative density of CBs is lower than that of graphite,as a result of this increased interplanar spacing. Generally, the stacks of micro-graphite layerare bound to functional groups generated during the manufacturing process. These includeO, hydrogen (H), and S containing functional groups.Figure 2.2: Structure of commercial carbon black (Figure 1 from E. M. Dannenberg, L.Paquin, and H. Gwinnell (2000). Carbon Black, Wiley books, © with permission from JohnWiley & Sons Inc.) [17].92.2. COMMERCIAL CARBON BLACK2.2.2. ProductionCB is produced during a partial combustion of hydrocarbons by a process termed aspyrolysis [17]. Thermal decomposition of oil (furnace process) to produce CB accounts fornearly 90% of the total CB production [21]. This process involves atomization of preheatedoil in a combustion gas stream leading to the formation and growth of CB particles. Theseparticles are extracted by quenching of exhaust gases containing the unburnt CB particles[17]. Typical temperatures for CB particle formation vary from 1400-1800 ◦C. SpecialityCBs, such as lamp black and acetylene black, are produced in small quantities and oftenhave a lower decomposition temperature (∼1100 ◦C) [18].2.2.3. Physical propertiesThe primary particle size, aggregate size, and agglomerate size are unique for thedifferent types of CBs. The primary particle and aggregate sizes are highly dependent on theprocessing conditions (temperature, time, etc.) and further the aggregates coalesce togetherto form weakly bound agglomerates [19]. For instance, an increase in the pyrolysis (thermaltreatment) temperature results in faster atomization of oil particles, resulting in a smallerprimary particle size [22]. Also, depending on how uniform the temperature distribution isin the furnace during pyrolysis processing, the particle size distribution varies. Also, longerreactions times allow formation of larger aggregates, because of increased time for theprimary particles to bind to each other. Aggregates are discreet colloidal entities, formedduring the early stages of CB manufacturing and can be spheroidal, ellipsoidal, linear, orbranched in shape [19]. Small ellipsoidal aggregates are formed when particle collisions arelimited in the reactor, whereas a branched structure is a result of increased rate of collisions[23]. The specific surface area of CB is another property directly related to the pyrolysisconditions. The particle size is inversely proportional to the surface area of the carbon blackdue to greater exposed surface. It is possible to also embed porosity into the CB surface (by102.3. EOL TIRES AS PRECURSORS FOR CB PRODUCTIONBoudard reaction at temperatures >900 ◦C) due to the decomposition of CO into C and CO2[22].Electrical conductivity of CB is primarily affected by its structure and surface area. Forinstance, a highly branched CB structure provides an easy channel for the movement ofelectrons in the material, thus improving the CB’s electrical conductivity. For low surfacearea CBs, it was found that the conductivity was related to the similarity of CB structure tographite [24]. This suggests that a low surface area CBs may have ordered micro-graphitelike sheets stacked together similar to a graphitic structure. Conductive CBs have a highelectrical conductivity (and a low resistance), with resistivity limited to <10 Ωcm [17]. Themost common commercially available conductive CB for battery anode application is knownby its trade name as “Super-P” known to have extremely high electrical conductivity (>5S/cm), high purity (>99 wt% C) and low surface area (<100 m2/g) [25, 26].2.3. EOL tires as precursors for CB productionThe storage of tires in landfills was banned by the European Commission in 1999 [27].Therefore, many studieswere conducted globally to explore the recycling of waste automotivetires. Tire rubber has a high CB content and is a promising precursor for rCB production.2.3.1. Composition of tiresTires are composed of vulcanized rubber and other reinforcement materials. Typically,automobile tire rubber contains 60-65% styrenebutadiene copolymer, 29-31% CB, 2-3% zincoxide (ZnO) and 1-2% sulphur (S) [4, 8]. Mining tires are mostly composed of natural rubberinstead of synthetic rubber commonly used in automotive tires [12]. Additives andreinforcements to mining tires include CB which is added for wear resistance, S is added forvulcanization (toughening or hardening), and ZnO is added to prevent ultraviolet (UV)degradation, provide wear resistance and enhance the blending of materials [12]. Although112.3. EOL TIRES AS PRECURSORS FOR CB PRODUCTIONthe exact composition of mining tires remains a trade secret for each manufacturer, thecomposition is typically 77% rubber, 16% steel (for structural support of tire frame), 6%fibre, and 1% inert matter [28]. The large quantity (∼60%) of organic mass can besuccessfully converted to C products by various processes. The structure of CB is known toaffect its properties (as discussed in Section 2.2). The following section provides details onthe properties of rCB materials.2.3.2. Properties of rCB derived from tiresrCB originating from tires is a mixture of commercial CB and polyaromatichydrocarbons (PAH) [18]. Tire-derived rCB generally has an amorphous structure with alow pore volume and a low surface area [29]. This amorphous structure consists of amixture of condensed graphitic sheets with randomly arranged aromatic units attached tothem, along with disordered C and carbonized rubber deposits [30, 31]. However, thisstructure can be modified, to a more graphitic form by high-temperature heat treatments.Rubber undergoes carbonization followed by graphitization during heat treatment at hightemperatures (>600 ◦C). This theory was discussed by Oberlin et al.[32] as early as 1984,where the amorphous rCB structure was seen to transform to a turbostratic structure duringa heat treatment [33]. This turbostratic structure is a partially graphitic structure of C, andexhibits improved electrical conductivity. Figure 2.3 shows the structural transformationand transmission electron microscope (TEM) images of typical CB materials during heattreatment.122.3. EOL TIRES AS PRECURSORS FOR CB PRODUCTIONFigure 2.3: Structural evolution and TEM images of carbon black with increase in heattreatment temperature showing: a) Amorphous carbon (Figure 5 from Z. Czigany andL. Hultman (2010). Interpretation of electron diffraction patterns from amorphous andfullerene-like carbon allotropes, Ultramicroscopy, vol. 110, pp. 815–819, © with permissionfrom Elsevier)[34], b) Turbostratic carbon (Figure 5 from © R. Gómez-Hernández, Y.Panecatl-Bernal, and M. Á. Méndez-Rojas (2019). High yield and simple one-step productionof carbon black nanoparticles from waste tires, Heliyon, vol. 5, published by Elsevier Ltd)[35].Figure 2.3a shows the amorphous structure of tire-derived rCB typically obtained duringlow temperature pyrolysis. Figure 2.3b shows the TEM image of a section of the primaryparticle of tire rCB obtained by Gomez et al.[35] at a pyrolysis temperature of 1000 ◦C. Thestriped regions in the image represent layers of graphene. The rCB had a disorderedgraphitic (turbostratic) structure with an interplanar distance of 0.335 nm. This distance wastypical of tire-derived rCB having an interplanar distance greater than graphite (>0.334 nm)likely due to random orientation of the graphitic layers and the presence of PAH betweenthem [36]. Similarly, Wang et al.[37] observed a reduction in the ID/IG ratio (ratio ofintensities of disordered and graphitic bands of carbon from Raman spectroscopy) at highheat treatment temperature (1000◦C), implying increased graphitic character. The G band at132.4. RECYCLING END-OF-LIFE TIRES FOR CB PRODUCTION1590 cm-1 was related to the graphitic structure of the sample representing sp2 hybridized Cwith C=C stretching vibrations, whereas the D band at 1355 cm-1 represented the disorder inthe structure, especially in the edges of micro-graphite like structures [38]. The partialgraphitization achieved by Wang et al.[37] was attributed to the alignment ofmicro-graphitic layers at high temperatures (>600 ◦C [39]) leading to the formation ofturbostratic rCB. Therefore, rCB from tires had very small (<1 µm) domains of graphite-likesheets with amorphous C, hydrocarbon and aromatic units making them so-called hardcarbons [35]. This structure is similar to that of commercial CB. The next section discussesthe major routes for recycling of EOL tires for rCB production.2.4. Recycling end-of-life tires for CB productionThere are several review articles available in the open literature on recycling of EOLautomobile tires. In the majority of cases, recycling was achieved primarily by thermaltreatment (termed “pyrolysis”) [40, 41]. Chemical treatments were used to purify the carbonfeedstock into the pyrolysis process, or to purify the product of pyrolysis (char) [42–45].The major pathways of recycling of tires are discussed in detail in the subsequent sections.2.4.1. PyrolysisWaste automotive tires (e.g., from cars, and light trucks) can be converted to a usableform of carbon by a process called pyrolysis. During pyrolysis, crumbs of waste tire are heattreated in an inert atmosphere at a broad range of temperatures (400-1000 °C) [41, 46–49].During this process, organics in the rubber are converted to low molecular mass compounds[50]. Typical products of pyrolysis are oils, gases, and solid C residues [41]. The solid Cresidues, which are a combination of CB along with volatiles and impurities, are termed as"char". During pyrolysis, non-carbon species such as H, nitrogen (N), S, and O are oftenvolatilized [51]. These volatiles contribute to the char’s porosity [52]. The surface area of the142.4. RECYCLING END-OF-LIFE TIRES FOR CB PRODUCTIONpyrolized char increased with an increase in the pyrolysis temperature, suggesting increasedevolution of volatiles frommaterials with an increase in temperature [41]. However, the yieldof C usually reduced with increasing pyrolysis temperature implying an inevitable removal ofcarbonaceous products by volatilization [53]. Table 2.1 summarizes the pyrolysis conditionsreported in the literature for producing chars from EOL tires.Table 2.1: Summary of pyrolysis conditions for the treatment of waste tires for recoveringcarbon black.Temperature Holding Time Pre-treatment BET surface Application Reference(◦C) (h) of tire area (m2/g)400 2 - 18 Adsorbent [46]450 2 in air 85 Adsorbent [54]500 5 H2O2 - Adsorbent [42]500 2 - 73 Adsorbent [55]500 5 H2O2 183 Adsorbent [56]500 1 - 89 Adsorbent [57]500 - - 65 Adsorbent [58]500 5 H2O2 - Adsorbent [43]500 5 - - Adsorbent [53]500 0.25 - - Adsorbent [59]500 2 - - Adsorbent [60]500 2 KOH 49 Adsorbent [44]570 1.67 - 61 Adsorbent [61]600 0.75 - - Adsorbent [62]600 3 - 61 Supercapacitor [63]600 1 - - Adsorbent [64]700 0 KOH 474 - [45]750 0 KOH 67 Adsorbent [65, 66]800 0.75 - 60 Adsorbent [67]800 1 - 126 Adsorbent [68]850 2 steam 34 Adsorbent [69, 70]900 - - 8 Adsorbent [71]1000 4 - 30 Electrical [35]1000 6 - 62 Adsorbent [48]As seen from papers in Table 2.1, the fixed carbon (FC) content of the char increasedwith an increase in the pyrolysis temperature and holding time [48, 49, 61, 62, 66]. Also, thevolatile content reduced with an increase in pyrolysis temperature likely due to their effectiveremoval [41]. Murillo et al.[48] experimented at 1000 ◦C pyrolysis temperature and obtained152.4. RECYCLING END-OF-LIFE TIRES FOR CB PRODUCTIONthe highest reported FC content (89.26%) and lowest volatile content (0.88%) of all tire charsreported in the literature thus far. Most researchers reported the presence of ash (inorganicimpurities) in the range 8.5%-26.2% [48, 49, 61, 67, 70]. These values were highly dependenton the type of tire used for the pyrolysis process. An effective way to reduce this ash contentwas chemical treatment of tire char [72].2.4.2. DemineralizationDemineralization is a leaching process resulting in the selective removal of species fromthe pyrolized char in an acid or base environment. Demineralization of tire rubber orpyrolyzed char was reported extensively in the literature [42–45]. Chemical treatmentswere reported to clean the tire-derived char, and also pre-activate it via the removal ofinorganic impurities. Such treatments can also help remove tar from the cross-linkedstructure of the char [73]. Iron (Fe), zinc (Zn), S and silicon (Si) were the most commonlyfound impurities remaining in pyrolized tire-derived char. The removal of these impuritieswas crucial for the production of rCB for battery applications, since the ash present in thechar affected the electrical conductivity of the rCB [74]. Lin et al.[75] reported successfulremoval of silica (SiO2) by using hydrofluoric acid (HF), instead of typically usinghydrochloric acid (HCl), likely due to the formation of H2SiF6 [76]. Kumar et al.[77] reportedsuccessful use of HCl and HF for complete removal of ash from the char. However,considering the requirements for safe handling of HF for large volumes, these chemicalsposed severe health and environmental challenges. HCl was more effective (93 wt% C) thansulphuric acid (H2SO4) (87 wt% C) for impurity removal from the char [54]. This indicatedthat impurities in tire-derived char had limited solubility in H2SO4. A few proposedreactions when HCl, potassium hydroxide (KOH) and sodium hydroxide (NaOH) were used,are listed in Equations 2.1-2.4 [76, 77]:FeS + 2HCl −−→ FeCl2 +H2S (2.1)162.4. RECYCLING END-OF-LIFE TIRES FOR CB PRODUCTIONZnS + 2HCl −−→ ZnCl2 +H2S (2.2)3 S + 6KOH −−→ 2K2S + K2SO3 + 3H2O (2.3)SiO2 + 2NaOH −−→ Na2SiO3 +H2O (2.4)NaOH was most effective in removing ash compared to HCl, nitric acid (HNO3), andH2SO4 during demineralization of char [78]. This was likely due to the effective removal ofSiO2 which was not possible with acidic reagents. If demineralization was performed beforepyrolysis, undesired side reactions may occur, thus reducing the final yield [76]. Also, sincetire rubber is chemically resistant (due to its stability in chemical environments), it wasmore difficult to treat large volumes of tire rubber [76, 79]. Therefore, this process wasgenerally performed after pyrolysis [74]. A significant hurdle for demineralization process isthe economy of large scale operations. Handling and disposal of large quantities of acidsand bases is challenging. Demineralization may also alter the surface chemistry,concentration of carboxylic and hydroxyl groups, and surface area of C materials [80, 81].For example, Han et al.[40] suggested that nitric acid treatment did not change the porestructure of C materials (measured by N2 adsorption experiments) but increased theconcentration of O containing functional groups. Saleh et al.[56] reported that increases intemperature during chemical treatments, increased the concentration of surface functionalgroups (particularly hydroxyl functional group) as seen in their fourier-transform infrared(FTIR) spectroscopy studies. The surface area of rCB can be further modified by activationexperiments as discussed in the following section.2.4.3. Activation of tire charActivation is the process of partial oxidation of C within its interstitial sites of its structure[82]. During this process, the surface area and porosity of the carbonized organic materialincreases [83]. The increase in the surface area is due to an increase of volume fraction of172.4. RECYCLING END-OF-LIFE TIRES FOR CB PRODUCTIONvoids, which are sites of high Van Der Waals forces. This force is responsible for the highadsorption capability of activated carbons (ACs) [11]. Activation can produce three types ofpores in the C structure: micropores (diameter <2 nm), mesopores (diameter between 2 nmand 50 nm), and macropores (diameter >50 nm) [84]. The volume of these different typesof pores determines the suitability of ACs for different applications. In general, to activatecarbon, two different activation methods can be used which are discussed in the next sections.2.4.3.1. Thermal activationThermal activation involves the heat treatment of carbon in a gaseous environment. Theactivation process can be separated into two stages: first where disordered C (from carbonizedrubber) is burned, followed by the second stage of burning the C from the aromatic rings[30, 85]. The most common environmental gases used for thermal activation are steam or CO2which assist to remove C from the material in the form of an oxide [11]. Thermal activationis mainly dependent on the reactivity of the char (disorder present in the structure) and theactivating agent used [30, 86]. Therefore, disordered C was easier to activate than orderedgraphite-like C. For activation with steam and CO2, the most common reactions taking placeare shown below [31, 82]:C + H2O −−→ CO+H2 (2.5)C + CO2 −−→ 2CO (2.6)Some researchers reported that CO2 is better suited for developing micropores in thetire-derived char in comparison to steam [87–89]. This was because CO2 was believed tostart the activation process with the formation of micropores and later their subsequentenlargement. In the case of steam, pore widening occurs from the beginning of theactivation process [89]. According to RPM (random pore model), the calculated activationenergy for C removal in the presence of steam (175.9 kJ/mol) was lower than that of CO2(197.7 kJ/mol), implying easier activation of carbon with steam [5, 30]. However, steam182.4. RECYCLING END-OF-LIFE TIRES FOR CB PRODUCTIONactivation possibly led to uncontrolled burning of the samples due to higher removal rate ofC atoms. A mixture of CO2 and steam was used for activation, and resulted in a largelymesoporous char [67]. This technique did not increase the Brunauer-Emmett-Teller (BET)surface area (SBET) value likely due to excessive burning resulting in uncontrolled removal ofC atoms [67]. Similarly, activation was performed using O2 leading to a maximum surfacearea of up to 100 m2/g for the AC [90]. These results indicated micropore widening anduncontrolled burning of the samples because of the presence of high concentrations of O2.2.4.3.2. Chemical activationChemical activation involves the mixing of the char with chemicals prior to activation.These chemicals then attach to the structure of the char and increase its reactivity inoxidizing environments. Therefore, these oxidants facilitate activation at a considerablylower temperature than activation using thermal treatments only. Some researchers addedthese chemicals to tire rubber before pyrolysis to promote rubber degradation because ofthis increased reactivity [46]. When developing AC for adsorbent applications, thesechemicals were also seen to incorporate carbonyl and hydroxyl functional groups, which ledto easier adsorption of targeted species by lowering the binding energy for adsorption ofmolecules [81, 91]. KOH was reported to be the most effective agent, facilitating activationof char through three stages [77]:1. Reaction of C and KOH to form K2O (at 700-800 °C) and K2CO3 (between 400-600 °C).K2CO3 −−→ K2O+ CO2 (2.7)2. Removal of carbon in the form of CO or CO2 (at >700 °C).6KOH + 2C −−→ 2K + 3H2 + 2K2CO3 (2.8)192.4. RECYCLING END-OF-LIFE TIRES FOR CB PRODUCTION3. Intercalation of K in the C lattice resulting in lattice expansion. After activation wascomplete, the material was typically washed with water or a mild acid to removepotassium metal, thereby leaving an expanded lattice.For KOH activation, the key factors affecting the SBET were the treatment temperatureand KOH:char ratio (i.e., impregnation ratio) [92]. A direct correlation between the SBET andimpregnation ratio was observed, where the SBET increased as the ratio increased due tomicropore enlargement [65, 77, 92]. Marquez et al.[65] performed chemical treatment oftires with KOH before pyrolysis and observed that the pre-treatment increased SBET of thechar. They observed an increase in SBET with an increase in impregnation ratio andtreatment temperature (upto 515 m2/g depending on the activation conditions). Mostauthors revealed that an impregnation ratio of 4 yielded the maximum SBET values[65, 77, 93]. This was most likely due to increased removal of C atoms with increased charreactivity; however, for ratios >4, uncontrolled micropore widening was expected. Thehighest SBET of 981 m2/g was obtained by performing H2O2 and HCl pre-treatment beforeactivation by removing ash and incorporating O2 in the char [81]. Al-Rahbi et al.[64] alsofound KOH activation the most effective for gaseous adsorption of NO compared to K2CO3,Na2CO3 and NaOH. KOH (being a strong base) became a catalyst for dehydrogenationreaction during the activation of the char. However, a major drawback of this method ofactivation was the cost of chemicals used and the need for neutralization of the char afterthe activation process was complete [94].One of the goals of examining different treatments on tire-derived rCB was to producebattery grade rCB material. The next section includes information on the use of rCB indifferent rechargeable battery systems.202.5. RECOVERED CB (RCB) IN BATTERY SYSTEMS2.5. Recovered CB (rCB) in battery systemsSeveral publications can be found in the literature on the use of recovered C materialsfor applications in Li-ion batteries. Precursors like biomass [95–99], coffee grinds [100, 101],tea [102], automobile tires [77, 103], proteins [104, 105], plastics [106], and hair waste [107]were carbonized to produce C suitable for possible use in Li-ion battery systems. Allprecursors were typically treated in an inert environment at high temperatures and fordifferent durations. The C obtained varied drastically depending on the source used, even ifthe carbonization conditions were the same. There is limited literature on the use oftire-derived rCB for Na, K, and Li-ion batteries [77, 103, 108, 109]. Majority of the Cproduced from automobile waste tires was used for adsorbent applications[57, 59, 81, 110–112]. However, recent literature reports on the use of ACs (with a highsurface area) from tires in supercapacitor [63, 74, 113], and battery [77, 108] applications.Tire-derived rCB appeared to be a promising source of electrode material for batteries.Kumar et al.[114] demonstrated the successful use of tire-derived AC as an electrode invanadium redox flow battery with a coulombic efficiency of 87% at 10 mA/cm2. The authorsreported a stable performance (up to 200 cycles) due to improved electrical conductivity ofthe AC by virtue of its turbostratic structure. SBET was believed to be a major factor affectingthe performance of the studied cells. There was a direct proportionality between SBET andthe discharge capacity of the cells [77, 115]. The high SBET value considerably reduced thecoulombic efficiency, resulting in irreversible capacity loss. This loss was also related toirreversible reactions between O- and S- containing functional groups (during the first cycleof charge/discharge) in the C matrix commonly found in tire-derived rCBs [116]. Theporosity of the rCB was another crucial factor that was seen to affect the performance ofbatteries. In general, microporous rCB enabled easier ion intercalation and reduced theirreversible capacity loss in comparison to rCB with larger pores. Therefore, a highmicropore volume was desired for tire-derived rCBs for battery applications [117, 118]. A212.5. RECOVERED CB (RCB) IN BATTERY SYSTEMSdetailed discussion on the use of tire-derived rCB for Li-ion batteries is included in Section2.7.Doping Cmatrixwith heteroatomswas seen to improve the capacity and rate performancein Li, K and Na-ion battery systems [119]. Doping provided a path for easy movement ofmetal ions, better wettability of the electrolyte, and improved electrical conductivity, therebyimproving the battery’s performance. Typical elemental dopants include N [120], S [121],Tin (Sn) [122], and P [119, 122]. These elements have a high theoretical capacity but poorcyclability. Sn for example, has issues related to high volume expansion during charge anddischarge cycles [122].Researchers successfully used S-doped C from tires as anodes in Na-ion [115], and K-ion[121] batteries. Li et al.[115] obtained a discharge capacity of 203 mA/g after 100 cycles ofcharging with tire-derived sulfonated rCB in a Na-ion cell. They reported a directcorrelation between the pyrolysis temperature and the energy density of a full cell (Figure2.4). A higher heat treatment temperature resulted in a more non-crystalline randomlyarranged nano-graphene layers, resulting in better Na-ion storage. They also attributed theincrease in capacity to the reduced surface functional groups and defects on the C matrixwith the increase in pyrolysis temperature. Also, a capacity of 155 mAh/g after 200 cycleswas obtained when tire-derived char pyrolyzed at 1100 ◦C was used as an anode in K-ioncell [121]. Recently, Gong et al.[119] successfully prepared phosphorous doped mesoporoustire-derived rCB for K-ion batteries and observed an improvement in the electricalconductivity due to doping. Electrochemical impedance spectroscopy (EIS) analysis revealeda reduction in impedance for doped C electrodes when compared to undoped C. The specificcapacity after 300 cycles was also lower (98.5 mAh/g) for C electrodes compared tophosphorous doped C (128.5 mAh/g). Therefore, doping AC matrix with elements proved tobe beneficial for obtaining high capacity Na and K-ion batteries.222.6. LI-ION BATTERIESFigure 2.4: A comparison of charge and discharge curves for Na-ion batteries with tire-derived carbon anodes pyrolyzed at different temperatures (Figure 3d from Y. Li, M. P.Paranthaman, K. Akato, A. K. Naskar, A. M. Levine, R. J. Lee, S.-O. Kim, J. Zhang, S. Dai,and A. Manthiram (2016). Tire-derived carbon composite anodes for sodium ion batteries,Journal of Power Sources, vol. 316, pp. 232–238, © with permission from Elsevier B.V. )[115].As seen in the examples discussed, there is a potential for tire-derived rCB and AC for highcapacity battery applications. This thesis was focused on the use of rCB for Li-ion batteryapplication. Therefore, the next section provides an overview of the Li-ion battery system.2.6. Li-ion batteriesCompared to other battery systems (e.g., lead acid, nickel-cadmium, nickel metal hydridebatteries, etc.), Li-ion batteries have a long cycle life, low self discharge rate and a rapidcharge capability [52]. Although Li-ion batteries are being used commercially in a numberof applications from alarm clocks to electric vehicles, there is still an opportunity forperformance improvement to increase their cycle life, cell capacity and reduce their cost.Figure 2.5 shows a typical cell consisting of an anode where Li-ions are accepted, a separatorwhich allows the passage of ions (while limiting flow of electrons) and a cathode rich inLi-ions. Li-ions migrate to anode from the cathode via the electrolyte during the process of232.6. LI-ION BATTERIESdischarging [123].Figure 2.5: Li-ion battery construction (Figure 1.12 from L. Zhen, Sajid Bashir, Jingbo Louise(2019). Technology Policy and Road Map of Battery, Springer Nature, © with permissionfrom Springer-Verlag GmbH Germany, part of Springer Nature) [123].Storage of Li-ion in electrodes can proceed via the following three electrochemicalreactions [123, 124]:• Alloying: Some elements may be introduced to the electrodes to alloy with Li (e.g., atlow potentials for alloying anodes). The most common alloying anode is silicon (Si)alloyed with C [125]. These electrodes typically have higher capacity than insertionanodes, however the volumetric change of these electrode materials is considerablyhigh (100% [124]) [126, 127].• Conversion: These electrodes are typically made of transition metal compounds MaXbwhere M is the metal and X is O, S, F, P, or N for anodes. Li reacts with X to form LiyX[126]. The “conversion” reaction taking place can be summarized as:MaXb + (b · n) Li −−→ aM + bLiyX (2.9)242.6. LI-ION BATTERIESConversion electrodes allow for a relatively higher capacity, but their cycling stabilityis poor. The use of a conductive matrix was seen to enhance the performance of thecells [126]. Conversion reactions are limited by irreversible capacity loss and requiresmaller electrode particle sizes (<20 nm) for greater reaction area [124]. Somecommon examples of the conversion electrode materials are Cr2O3, MnO2, Fe2O3,CuO, and SnO2[124, 127].• Insertion: Insertion electrodes work on the principle of intercalation of Li-ions in theelectrode matrix. The atomic structure of electrode material is most commonly layered,spinel or olivine [124]. The most common insertion anodes are made of graphite andtitanium-based compounds, while cathodes typically contain LiCoO2, LiFePO4 or V2O5.These electrodes have high stability during cycling, but their capacity is low.2.6.1. CathodesThe cathode is the positively charged electrode in a battery system. Cathode materialsare generally transition metal compounds or oxides with layered, spinel or olivine structuresto allow efficient Li-ion intercalation. The main requirements of cathode materials are a highGibb’s free energy on reaction with Li, insolublities in the electrolyte and the ability to hostLi-ions [128]. Cathode materials have lower capacity than anodes (100-300 mAh/g [125]) andcontinued research is ongoing to increase their capacities to match up to anode materials[124]. Since research on cathode materials is limited and not understood well (apart from fewelectrode materials such as LiCoO2), this work was focused on the use of rCB (as anode andadditive) in commercially available and well understood anode materials.2.6.2. AnodesThe anode is the negatively charged electrode in a Li-ion battery system, and acts as ahost for Li-ions to reversibly intercalate and deintercalate during charging and discharging252.6. LI-ION BATTERIESrespectively. The anode in a battery system is responsible for storing Li-ions during celldischarging [123]. Thus, anode materials must be capable of accepting Li-ions duringcharging. During the first cycle of discharging, anodes develop the solid electrolyte interface(SEI) film as a result of an electrochemical reaction with the Li-ion containing electrolyteand the electrode [129]. This SEI layer is electrically insulative but allows passing of Li-ions.On continued charging and discharging, Li metal can deposit on the anode, particularly atlow potentials, and the deposit layer thickness may grow with continued cycling. Duringthis process, Li dendrites form on the electrode and result in the rupture of the separatorand eventual short circuit of the cell [126]. Therefore, the anode materials are critical forbattery safety performance. The two most common commercially used insertion anodesystems are C (graphite anodes) and lithium titanate (LTO) anodes. These are discussed indetail in the following sections.2.6.2.1. Carbon anodeCarbon is one of the most common anode materials used in Li-ion batteries. This is dueto its high volumetric stability, low cost, and a low de-lithiation potential [125]. When a Canode is charged/discharged for the first time, reduction of electrolyte species occurs on itssurface along with Li interaction. This is termed as irreversible capacity loss and the SEIlayer formed in C based anodes in LiPF6 electrolyte mostly comprises of CH2OLi2 [130]. Theirreversible capacity was generally associated with the SBET of the C material andirreversible reactions between O and S containing functional groups in the C matrix[116, 126]. Porosity of the electrode material was another crucial factor that affected theperformance of the anode. If it was too low, it increased the cell impedance, reduced thecapacity, lowered the rate performance, and limited ionic transport. Conversely, if porositywas too high, it increased the irreversible capacity drop [126].For graphitic anodes, energy storage in the C materials comes from the intercalation ofLi ions in between the graphite layers. Li intercalation occurs over a narrow potential range262.6. LI-ION BATTERIES0.125 V vs Li+/Li [131]. For every six C atoms, one Li-ion intercalates in graphite giving it atheoretical discharge capacity of 372 mAh/g [125]. To increase the energy density obtainedfrom C anodes, several nano-structured carbonaceous materials were used as electrodes[132]. For non-graphitic anode materials, intercalation began at 1.5 V [133]. The maximumcapacity obtained from non-graphitic anodes exceeded 372 mAh/g, because nano-structuredC materials formed intercalation compound LiC2 instead of LiC6 [134]. This higher capacity(>372 mAh/g) could also be due to the interaction of H atoms present in the C structure withLi ions [116]. The molecule C2H2Li was known to form on reaction with H [135]."Carbotron p" is a hard C material developed by Kureha Chemical with a discharge capacityof 500 mAh/g. The interplanar distance in this material was 0.38 nm vs 0.34 nm for graphite(resulting in only 1% volume expansion compared to 10% for graphite) [129]. However, suchhard carbon electrodes in general have large irreversible capacity (due to Li entrapment) andare hence unlikely to be commercialized [116, 125].2.6.2.2. LTO anodeLi4Ti5O12 (LTO) was successfully used as a commercial anode material because of itshigh stability, high volumetric capacity, and long cycle life [125]. This was possible sinceLTO accepts Li-ions by transitioning from spinel structure to rock salt structure without anoticeable change in the lattice parameter [136]. The theoretical gravimetric capacity ofLTO anodes is 175 mAh/g, since three Li ions are accepted by the anode forming theLi7Ti5O12 phase [137, 138]. Although the gravimetric capacity of LTO anodes is lower thanthat of graphite, LTO anodes are extremely stable and exhibit almost no formation of Lidendrites because of the high potential (>1 V) involved during discharge [139]. They have astable charge and discharge plateau at 1.5 V and a long cycle life [136, 140, 141].272.6. LI-ION BATTERIES2.6.2.3. Limitations of graphite and LTO anodesLi-ion working principle is well understood for graphite and LTO electrodes. However,these typical configurations allow for relatively low capacities (372 mAh/g for graphite) [1].Also, graphite undergoes uniaxial 10% strain along the edge planes during Li-intercalationand deintercalation [125]. SEI layer may become damaged due to this strain. As discussedpreviously, the maximum capacity obtained from non-graphitic anodes may exceed 372mAh/g [134]. Therefore, researchers seek anode materials with defects and nano-voidswhich lead to a high gravimetric capacity [125]. Researchers have tried to use amorphous Cexclusively or dope it with graphite to overcome this challenge. These electrodes weresuccessful in imparting high specific discharge capacity to the cells [142].LTO anodes have extremely low electrical conductivity (5 x 10-7 S/cm) and hence areusually doped or coated with an electrically conductive material in order to enhance theircapacity [143, 144]. Typically the conductive material is CB.2.6.3. Carbon conductive additivesIn order to enhance the solid state diffusion of Li-ions and electrical conductivity inactive materials, conductive materials are often added to electrodes [145]. These additivesdo not contribute to the gravimetric capacity of the electrode, but only enhance theirelectrical conductivity by lowering the cell’s internal resistance [146]. The role of the Cadditives in cathodes is illustrated in Figure 2.6. The C coating in this case (black layer) isacting as the conductive additive in the cathode to allow easy transport of electrons andmovement of Li ions from the active material. The binder, shown by the grey area, providesgood adhesion of electrode materials to the current collector. Similarly, conductive additivesare blended to anodes to improve their overall electrical conductivity. The electrode with aconductive additive can be produced by various methods like in-situ C coating (by heating),milling, chemical vapour deposition, or hand mixing [147].282.7. TIRE-DERIVED RCB FOR LI-ION BATTERIESResearchers have used different carbon additives in Li-ion battery electrodes: graphene[145], C nanotubes (CNTs) [148, 149], reduced graphene oxide (rGO) [150], C fibres [151] andCB [2]. Graphene, CNTs, rGO with a high SBET reduced the volumetric energy density andhad a reduced dispersibility in the electrode slurry, thus being a less efficient additives [152].Despite improvement in some properties (electrical conductivity, gravimetric energy density)with other additive materials, the most promising commercially feasible conductive additiveremains conductive CB [25].Figure 2.6: Use of carbon additives in Li-ion cathode. (Figure: Graphical abstract N. Kwon,D. Mouck-Makanda, and K. Fromm (2018). A Review: Carbon Additives in LiMnPO4- andLiCoO2-Based Cathode Composites for Lithium Ion Batteries, Batteries, vol. 4, p. 50)[147].2.7. Tire-derived rCB for Li-ion batteriesPublished literature suggests that tire-derived rCB can be successfully used in Li-ionbattery systems. The resulting performance of the modified cells was highly dependent on292.7. TIRE-DERIVED RCB FOR LI-ION BATTERIESthe structure and purity of the rCB. The structure and purity were directly affected by thepyrolysis of EOL tires, demineralization, and activation treatments performed on thetire-derived char. Table 2.2 shows the carbonization (pyrolysis) conditions for conversion oftires (rubber) to battery grade C materials. It was reported that higher pyrolysistemperatures were necessary for rCB production for battery applications (Table 2.1) in orderto remove surface functional groups and graphitize the material [115]. It was also reportedthat a discharge capacity of 880 mAh/g could be obtained from rCB derived from wasteautomobile tires [77]. However, the irreversible capacity loss from the cells was high,possibly due to the high SBET and remaining surface functional groups in the rCB modifiedelectrodes. Demineralization was also performed in all studies (on rCB from tires for Li-ionbatteries) likely to remove the ash present in the samples effectively removing majormetallic impurities from tire-derived char.Table 2.2: Carbonization charateristics of EOL tires used for production of carbon for Li-ionbattery applications.Reference Temperature(◦C)Holdingtime (h) GasChemicaltreatmentDischargecapacityafter 1stcycle(mAh/g)Stabilizeddischargecapacity(mAh/g)Kumar et al.[77] 800 1 N2 yes 1500 880Gnanaraj et al.[103] 1100 2 N2 yes 374 247Parans et al.[109] 1100 0.25 - yes 949 379Naskar et al.[108] 1000 - N2 yes 545 387Activation of tire-derived char proved to be an important step in preparing high capacityLi-ion cells. The rCB was activated using KOH with different impregnation ratios [77]. Theresults from cyclic performance of resulting batteries are included in Figure 2.7. As seen inFigure 2.7, the specific capacity was influenced by the KOH impregnation ratio and, in turn,the SBET value. During cycling, the capacity fade was negligible (<5%) after the irreversible302.7. TIRE-DERIVED RCB FOR LI-ION BATTERIEScapacity drop in the first cycle. However, as expected (due to the high SBET values and thepresence contaminants in the tire-derived char), the irreversible capacity drop after the firstcycle of charge-discharge was high for the sample activated at 800 ◦C (a difference of 700mAh/g). Modification of the pore structure of tire-derived ACs (improvement in microporevolume) was suggested to help avoid the irreversible capacity drop.Figure 2.7: Cyclic performance of tire-derived rCB at 50 A/g for untreated pyrolyzedchar (UPC), acid treated char (CA) and KOH activated char (CK-n with ”n” specifyingthe impregnation ratio) (Figure 10 from R. Kumar and A. Sharma (2018). Morphologicallytailored activated carbon derived from waste tires as high-performance anode for Li-ionbattery, Journal of Applied Electrochemistry, vol. 48, pp. 1–13, © with permission fromSpringer Science Business Media B.V., part of Springer Nature) [77].Elemental doping of rCB anode materials with S was also seen to improve the cell’sperformance [103, 108]. Naskar et al.[108] studied the cycling behavior of S-doped Celectrode in Li-ion batteries (see Figure 2.8). In this study, tire rubber was treated with anoleum (H2S2O7) bath before pyrolysis to yield sulfonated rubber. After pyrolysis, theS-doped char was used in fabricating the anode. The cell’s capacity reached 390 mA/g after100 cycles, which was better than the traditional graphite anode cell used commercially. Theincorporation of S increased microporosity and the number of Li-insertion sites, leading tothe increased capacity. Li-ions were intercalated between the graphitic layers of C and in312.8. SUMMARY OF LITERATUREthe pores as well as sites containing S. Other researchers reported a capacity of 247 mAh/g[103] and 385 mAh/g [109] from sulphonated rCB derived from EOL tires.Figure 2.8: Cycling performance of carbon (control tire rubber derived) anode at 0.1C(Figure 7c from A. K. Naskar, Z. Bi, Y. Li, S. K. Akato, D. Saha, M. Chi, C. A. Bridges, andM. P. Paranthaman (2014). Tailored recovery of carbons from waste tires for enhancedperformance as anodes in lithium-ion batteries, RSC Advances, vol. 4, p. 38213, © withpermission from RSC advances)[108].Literature suggests that rCB from automobile tires is a potential candidate for electrodematerial in Li-ion battery systems. However, there is paucity of research on the use oftire-derived rCB as additives to commercially available anode materials and therefore this isanother potential application of rCB which needs to be studied. According to the best of theauthor’s knowledge, no research has been conducted focusing on the recovery of miningtire-derived rCB in Li-ion battery systems.2.8. Summary of literatureThe following are the key findings from literature review conducted for this research:• CB is commercially produced by the thermal decomposition of organic materials(oil/natural gas). Furnace process is the most common manufacturing technique for322.8. SUMMARY OF LITERATUREthe production of CB.• The demand for CB is expected to increase in the near future and hence other methodsfor its production need to be explored. Recycling wastes for the recovery of CB wouldalso be an environmentally friendly process.• Since waste tires have a CB content of ∼30%, they are a promising precursor for CBproduction via tire recycling. Recycling begins by thermal treatment (400-1000°C)termed as "pyrolysis" in an inert atmosphere.• The "char" produced after pyrolysis of tires still has a high ash content (∼20%). Theinorganic ash impurities can be removed by chemical treatment or demineralization.• Demineralization using acids such as HCl, H2SO4, HNO3, and HF was most commonlyreported in the literature to remove metallic impurities. Bases such as KOH and NaOHwere also used for the removal of SiO2 from the char.• Activation could be performed on the tire char to increase its surface area. Thermalactivation involves heat treatment of tire char in an oxidizing environment (steam, CO2)while chemical activation involves a chemical treatment prior to activation.• The gravimetric capacity of graphite is restricted because of its structure. Researchershave suggested the use of non-graphitic anodes with defects and voids to overcomethis challenge. However, a major drawback of using non-graphitic materials is theirreversible capacity loss.• LTO anodes have extremely low electrical conductivity and hence a more conductivematerial, usually, a conductive CB is added as an additive in such anodes.• Literature has revealed the use of different carbon based additive materials likegraphene, nano-tubes, CB for use in electrodes. CB has proven to be the most effectivein imparting high electrical conductivity of anode.332.8. SUMMARY OF LITERATURE• Researchers have demonstrated that a gravimetric capacity of 880 mAh/g in a Li-ionbattery system could be obtained from the use of AC derived fromwaste tires. However,such a cell had a high irreversible capacity loss after the first cycle of charging anddischarging.• According to the best of the author’s knowledge, no research has been conductedfocusing on the recovery and testing of mining tire-derived rCB in Li-ion batterysystems.34Chapter 3: Experimental ProcedureThis chapter provides an overview of the experiments conducted in this research. Detailspertaining to the treatment of raw carbon char, its purification, and activation along with thecharacterization and the evaluation of the performance of Li-ion cells are described.3.1. IntroductionAs discussed in Chapter 1, the focus of this research was to upgrade the raw carbon charand explore its use for Li-ion battery applications. As a result, the experiments in this researchwere divided into two major categories:1. Processing of raw carbon char: The first part of this research focused on theprocessing and purification of the raw carbon char, including chemical leaching, heattreatment, and activation investigations. These experiments aimed to modify thestructure and chemical composition of the raw carbon char to make it suitable forenergy storage applications.2. Fabrication and testing of Li-ion coin cells: The second part of this researchexplored the use of rCB as anode additives and anode materials for Li-ion batteries.The experimental details focus on the fabrication, electrochemical testing, andanalysis of Li-ion cells.The precursor material purity and structure significantly affected the electrochemicalperformance of the Li-ion cells. Therefore, the next section discusses the details of thematerials used in this research.353.2. PRECURSOR MATERIALS3.2. Precursor materialsThe following section includes information on the as-received carbon materials.3.2.1. Raw carbon charRaw carbon char obtained from Kal Tire Mining Tire Group (received in May 2018) wasused as the starting raw material for all experiments performed in the current research. Thepyrolysis conditions to create this raw carbon char are proprietary IP and were not revealed.Figure 3.1 shows an SEM image of the raw carbon char.Figure 3.1: SEM (SE) image of raw carbon char used as precursor for all experiments.Table 3.1 provides the chemical composition (obtained from SEM-EDS analysis) of theraw carbon char. The error in measurement of impurities present in the raw carbon char was363.2. PRECURSOR MATERIALSrelatively high, (∼0.7 wt%) as seen in Figure A.1. Inhomogeneities in the concentration ofimpurities were possibly related to settling or segregation of the raw carbon char particles instorage containers. However, major contaminants in all cases were Zn, S, and Si, with tracesof other metals.Table 3.1: Composition of raw carbon char from SEM-EDS analysis.Element Concentration (wt%)C 80.93 ± 0.67O 10.48 ± 0.83Zn 3.77 ± 0.30S 2.24 ± 0.05Si 1.41 ± 0.03Na 0.51 ± 0.07Mg 0.21 ± 0.02Fe 0.22 ± 0.02Ca 0.14 ± 0.02K 0.09 ± 0.01Cl 0.00 ± 0.003.2.2. Super-P conductive carbonSuper-P was obtained from Alpha Aesar (catalog number AAH3025314). It is acommercially available conductive carbon black used for battery applications. In thisresearch, Super-P was used as a bench-marking material. Figure 3.2 shows the structure ofSuper-P. The primary particles appeared to have a round shape and readily formedagglomerates. SEM-EDS analysis revealed the absence of non-metallic impurities in thesample. The carbon content was 91 wt%, and the remainder was O. Proximate analysisresults revealed FC content of 99.6%, volatile content of 0.15%, and ash content of 0.1% inSuper-P CB. Further, SBET of Super-P CB was found to be 77 m2/g, with ID/IG= 0.86.373.3. UPGRADING OF RAW CARBON CHAR FOR LI-ION BATTERIESa bFigure 3.2: SEM (SE) image of Super-P® conductive carbon used in this research: a) At 200x,b) At 100Kx.3.3. Upgrading of raw carbon char for Li-ion batteriesThe techniques used for the processing of raw carbon char are described in this section.The two main routes for the modification of the char was by chemical and heat treatments.Chemical treatments were performed to purify the raw carbon char, whereas heat treatmentwas performed to remove volatiles and alter the carbon matrix structure.3.3.1. Chemical treatment of raw carbon charChemical treatments were performed to remove inorganic impurities present in the rawcarbon char. All acids and bases for the chemical treatments were obtained from FisherScientific, and the solutions of various concentrations were made by diluting them in reverseosmosized (RO) water. Specified quantities of raw carbon char were added to the acids andbases of different molarities. The mixing (leaching) experiments were done in a fumehoodwith hot plates and magnetic stir bars rotating at 250 rpm. After the leaching process (i.e.,383.3. UPGRADING OF RAW CARBON CHAR FOR LI-ION BATTERIESacid or base treatment) was finished, the leached samples were washed (using RO water)until a pH of 7 was obtained. The slurry was then filtered (using grade 1 Whatman filterpaper). Table 3.2 includes the list of chemicals used with their product information.Table 3.2: Summary of product numbers for chemicals used in this thesis.Chemical used Catalog number Physical state of chemicalHCl A144-212 LiquidHNO3 A200-212 LiquidH2SO4 A300-500 LiquidNaOH S3185 PelletsKOH P250-1 Pellets3.3.1.1. Optimization of chemical treatment experimentsSeveral acids and bases were used for chemical treatments (as seen in the Table 3.2).These experiments were aimed to identify the ideal chemical (acid/base or both) required topurify the raw carbon char. The temperature effect for leaching was not considered in theoptimization experiments, since higher temperatures would introduce additional functionalgroups to the recycled carbon black (rCB) lattice, which would have an undesirable effectfor battery applications [56]. Table 3.3 includes information about the different chemicalsused for leaching experiments. Since high error was observed in EDS analysis of raw carbonchar batches, the ratio of impurity concentration to carbon was calculated and used forcomparing different acid and base treatments. This ratio of Zn/C, Si/C, S/C was furthermultiplied by 100 to convert to percentage. HCl and NaOH were found as the most effectivein removing impurities from the raw carbon char (Chapter 4). Therefore, these chemicalswere selected for further treatment of the raw carbon char. Further, only values withoutnormalization were used to compare SEM-EDS analysis results to minimize error betweenmeasurements.393.3. UPGRADING OF RAW CARBON CHAR FOR LI-ION BATTERIESTable 3.3: Summary of different chemical treatments performed in this thesis for a leachingtime of 2 h and slurry ratio of 50 g/L.Chemical used MolarityHCl 5 M and 10 MHNO3 5 M and 10 MH2SO4 5 M and 10 MNaOH 5 M and 10 MKOH 5 M and 10 MThe raw carbon char (in grams) to chemical (in litres) ratio was termed as the "slurryratio" in this research. It was expected that the slurry ratio would have an effect on theleaching behavior, since the chemical species present in the mixture selectively leach out atg:L ratios. On studying the effect of slurry ratios (section 4.1.3 and section 4.2.3), it was foundthat a value of 50 g of raw carbon char per litre of HCl and NaOH solution were optimumfor chemical treatments. A slurry ratio greater than this value would result in the solidsfloating to the top of the flask during leaching. As seen in the literature, the crucial factorsaffecting chemical leaching experiments were the molarity of chemicals and leaching time[153]. These experiments were performed to optimize the time required for leaching at agiven concentration. Table 3.4 shows different slurry ratios, leaching times and molaritiesemployed in this research.Table 3.4: Summary of different slurry ratios, molarities and leaching times used in thisthesis for HCl and NaOH leaching.Molarity Leaching time (h) Slurry ratio (g/L)1 M 24 10, 20, 50, 801 M, 5 M, 10 M 24 505 M 2, 12, 18, 24 50After extensive optimization experiments, combined acid and base leaching was selectedto clean the raw carbon char. The details pertaining to processing of raw carbon char to formleached CB is discussed in the next section.403.3. UPGRADING OF RAW CARBON CHAR FOR LI-ION BATTERIES3.3.1.2. Leached CBAs will be discussed in Section 4.3, a combination of 5 M HCl and 10 M NaOH was mosteffective for cleaning the raw carbon char. As a result this treatment was performed on allraw carbon char samples intended for further experimentation. This sample (treated with 5M HCl and 10 M NaOH) was termed as "leached CB" throughout this document. The rawcarbon char was treated first with 5 M HCl for a leaching time of 2 h, neutralized with ROwater and air dried, and then treated with 10 M NaOH for 2 h. After base treatment, the 5 MHCl + 10 M NaOH treated raw carbon char was neutralized using RO water before drying inair. Figure 3.3 includes a schematic representation of the process to manufacture leached CB.Figure 3.3: Description of combined acid and base treatment for preparation of leached CBfrom raw carbon char.Leached CB production was improved using a pressure filtration system instead of thefilter paper as shown in Figure 3.4. The pressure filter consisted of a stainless steel mesh for413.3. UPGRADING OF RAW CARBON CHAR FOR LI-ION BATTERIESfiltering. The base of the pressure filter was a stainless steel plate with 3 layers of stainlesssteel mesh and Whatman Grade 1 filter paper sandwiched between them (Figure 3.4b). Theassembly of filters was held firm with the help of a teflon ring. About 10 L of acid or baseslurry (CB suspended in chemical) was poured on top of the filters. The filter was then closedand an air compressor (RIDGID 200 psi Quiet Compressor) was used to apply pressurized air(40 psi). The filterate (chemical) was collected in a Teflon bucket and later discarded. Theleached CB (∼500 g) collected on the stainless steel mesh was collected in a container anddried overnight in a fumehood.abFigure 3.4: Pressure filtration system used for filtration of chemically treated rCB afterchemical leaching: a) Pressure filter, and b) Stainless steel mesh assembly.423.3. UPGRADING OF RAW CARBON CHAR FOR LI-ION BATTERIES3.3.2. Heat treatment of leached carbon blackHeat treatment was performed on the "leached CB" material (treated with 5 M HCl and 10M NaOH), due to its highest purity. Netzsch DTA-TG (STA Jupiter F3) unit was used for heattreatment experiments, as shown in Figure 3.5. Alumina sample holder and crucibles wereused for all the experiments, with flowing nitrogen (50 ml/min) as ambient environment. Asample size of 20 mg was employed for all the experiments. Peak position was determinedusing the Netzsch post analysis software.Figure 3.5: Netzsch STA Jupiter F3 DTA/TG unit.Leached CB was heated up to 1000 °C at different heating rates, and held isothermally fordifferent durations. Table 3.5 provides the details on heat treatment experiments performedwith varying temperatures, heating rates and holding times.433.3. UPGRADING OF RAW CARBON CHAR FOR LI-ION BATTERIESTable 3.5: Summary of heat treatment experiments performed in this thesis.Target temperature (°C) Heating rate (°C/m) Holding time (h)900, 950, 1000 10 11000 10 1, 2, 3950 5, 10, 25 13.3.3. Activation of leached carbon blackActivation was performed to increase the surface area of the leached CB and to modify itsstructure. Leached CB (treated with 5 M HCl and 10 M NaOH) was used as the input materialfor all activation experiments. Activation experiments were carried out with activating agentssuch as KOH pellets and CO2 gas. Steam was not used for these experiments since steamimparted macroporosity in ACs from tire char, as reported in literature [87, 89]. All activationexperiments were performed in a horizontal tube furnace with a continuous flow of N2. Thetube used was 1" diameter 316 stainless steel and all samples were heated at 5 °C/min. Theburnoff values were calculated using the difference in initial and final weights of the samples(before and after activation) divided by the initial weight.For activation with KOH, leached CB was mixed with KOH pellets using a pestle andmortar (for 10 mins) and the mixture was placed into a nickel crucible. The differentKOH:leached CB ratios (impregnation ratios) along with other parameters are included inTable 3.6. After the experiment, the samples were washed with RO water (to reach a pHvalue of 7) to eliminate any remaining KOH. All samples treated with KOH were labeledusing the following terminology “KOH AC (target temperature-holding time-KOH:CBratio)”. For example, the sample heated to 900 °C for 2 h with a ratio of 4:1 was labeled asKOH AC (900-2-4).Table 3.6: Summary of KOH activation experiments performed in this thesis.Target temperature (°C) Impregnation ratio Holding time (h)700, 800, 900 4 2900 1, 2, 4, 5 2900 4 1, 2, 3443.4. FABRICATION AND TESTING OF LI-ION CELLSFor CO2 activation experiments, the samples were heated from 800 °C to 1000 °C underflowing N2. Once the target temperature was reached, the N2 gas supply was switched to CO2.The samples were held isothermally at 900°C for different durations (1, 2, 3, and 6 h). Sampleswere then cooled under N2. All samples treated with CO2 were labeled using the terminology“CO2 AC (target temperature-holding time)”.3.4. Fabrication and testing of Li-ion cellsThis section describes the methods for the fabrication of Li-ion half cells and theirsubsequent electrochemical testing. The purpose of these experiments was to evaluate theuse of the rCB as an additive for electrodes or as anodes in Li-ion systems. Figure 3.6 showsthe various components required for the fabrication of Li-ion cells. The instruments andtools used were available at Dr. Jian Liu’s research laboratory (Advanced Materials forEnergy Storage Lab) at UBCO. Two different electrodes were made using rCB; these aredescribed in the subsequent sections.453.4. FABRICATION AND TESTING OF LI-ION CELLSa bc dFigure 3.6: Fabrication of Li-ion half cell: a) Pestle and mortar, b) Doctor’s blade, c) Vacuumoven, and d) Punching station.3.4.1. rCB as additive in LTO batteriesLTO powder and different grades of rCB were mixed using a pestle and mortar for 30 mins(see Figure 3.6a) at a ratio of 8:1. After mixing, a 5 wt% solution of polyvinylidene fluoride(PVDF) in N-methyl-2-pyrrolidone (NMP) was added at the specified quantity. The slurry wassubsequently mixed for 60 mins. The electrode’s final composition had a ratio of 8:1:1 (LTOpowder:Leached CB:PVDF). The slurry was pasted on a Cu foil (wiped with alcohol) usinga film casting doctor blade (see Figure 3.6b), to yield a coating with a thickness of ∼50 µm.The coated Cu foil was then dried in a vacuum oven overnight at 60 °C to evaporate the NMP463.4. FABRICATION AND TESTING OF LI-ION CELLSsolution (shown in Figure 3.6c). Electrodes were punched out (12 mm in diameter) and storedin an airtight container after the drying process (Figure 3.6d).3.4.2. rCB as active material in Li-ion batteriesLeached CB was mixed with PVDF (dispersed in NMP solution (5 wt% PVDF, 95 wt%NMP)) at a ratio of 9:1 respectively using a pestle and mortar for 60 mins. The slurry waspasted on a Cu foil cleaned with alcohol using the doctor blade to yield a coating with athickness of 50 µm. The coated Cu foil was then dried in a vacuum oven overnight at 60 °Cto evaporate the NMP solution. 12 mm diameter electrodes were punched out and stored inan airtight container after the drying process (Figure 3.6d).3.4.3. Electrochemical testing of Li-ion half cells2032-coin cells were fabricated in the Advanced Materials for Energy Storage Lab atUBCO. Li foil was used as the anode, while the cathode was the material being tested. Astainless steel spring and plate were used in the assembly. Polypropylene (PP) (Celgard)separator and 80 µl of electrolyte (1 M lithium hexafluorophosphate (LiPF6) in ethylenecarbonate (EC) and diethyl carbonate (DEC)) (ratio of 1:1) electrolyte were used. The cellswere assembled in an Ar glovebox with moisture and oxygen levels below 1 ppm. Coin cellswere allowed a soaking time of 12 h before electrochemical testing. The cells were chargedand discharged for a total of 100 cycles at 0.5 C. However, the results included in this workwas up to 50 cycles because no new information was revealed with continued cycling. LTObattery anodes were tested between 1-3 V (higher de-lithiation potential than C anodes),whereas carbon anodes were tested between 0-3 V. The different grades of rCB used forelectrochemical testing are included in Table 3.7. Electrochemical tests were performed forboth LTO anodes and C only anodes. Electrochemical Impedance Spectroscopy (EIS) wasperformed on all cells before cycling to understand the chemistry of the cells usingBio-Logic SAS Model-SP-150 potentiostat (Figure E.3). The cells were tested from 1000 KHz473.4. FABRICATION AND TESTING OF LI-ION CELLSto 10 mHz with 6 points captured per decade at an amplitude of 10 mV. Zsimpwin softwarewas used for curve fitting of EIS results. The information on curve fitting and goodness of fitfor different cells tested is included in Appendix C (Figure C.9). The equivalent circuit usedto define the electrical parameters calculated from curve fitting was a modified Randle’scircuit commonly seen in the literature (Figure 3.7) [154, 155]. Rs refers to the solutionresistance, Rct was the charge transfer resistance, Cs was the capacitance and W was theWarburg impedance. Further, the CO2AC (1000-3) doped LTO cell was also analyzed withEIS after cycling experiments were complete. This cell had the most promising results andwas therefore selected for further analysis. The circuit used for curve fitting of results aftercycling consisted of an additional capacitance and resistance due to the presence of the SEIlayer as seen in Figure 6.25. Additional information pertaining to selection of the model isbeyond the scope of this work but can be found in References [156, 157]. Rate-tests werealso performed on all the cells to see their performance at different charge and dischargerates. All cells were tested at 0.1 C, 0.2 C, 0.5 C, 1 C, 2 C and 0.1 C for 10 cycles each.Figure 3.7: Modified Randle’s circuit: Equivalent circuit used for curve fitting of EIS results.483.4. FABRICATION AND TESTING OF LI-ION CELLSTable 3.7: Different grades of rCB tested for electrochemical performance in LTO and Canode systems.rCB grades tested at 0.5CRaw carbon charLeached CBLeached CB+ heat (950 °C, 1 h, 10 °C/min)KOH AC (900-2-4)CO2 AC (1000-3)The setup for the electrochemical testing station is shown in Figure 3.8. Newaresoftware was used to set up the testing parameters as well as exporting the results. Theamount of active material was calculated using the electrode weight measured usingMettler-Toledo Model-XPR2 microbalance (Figure E.4). Since 80% (ratio of 8:1:1) of theelectrode total weight was LTO (for LTO anodes) and 90% (ratio of 9:1 for C anodes) wascarbon, the total weight was multiplied by these values to yield the weight of activematerials. The charge-rate (C-rate) was determined as 372 mAh/g and 175 mAh/g for C andLTO anodes, respectively from literature [125]. The values of voltage range, current,number of cycles and the weight of active materials were entered in the Neware software(Figure E.2). Once cycling was complete, the cells were disassembled in an Ar gloveboxusing a hydraulic press. EC:DEC (1:1) solvent was used to wash of any remaining salt on theelectrode surface. The electrodes were dried overnight in the glovebox and stuck on analuminum stub using double sided carbon tape. SEM analysis was performed on all C anodeelectrodes (after cycling) to study the morphology of rCB after cycling. The LTO anodes(LTO+ KOHAC (900-2-4), CO2AC (1000-3)) were also analyzed using SEM.493.5. MATERIAL CHARACTERIZATION TECHNIQUESFigure 3.8: Electrochemical testing station for Li-ion half cells.3.5. Material characterization techniquesThe following materials characterization techniques were employed to study the carbonmaterials produced through different processes. The images of some of the instruments usedin this work are included in Figure E.4 (Appendix E).3.5.1. Skeletal density measurementThe skeletal density of rCB was measured using gas pycnometer AccuPyc II 1340 fromMicromeritics at DLR in Cologne, Germany. The rCB was weighed and inserted into astainless steel sample holder of a known volume. Helium gas was then purged in the steel503.5. MATERIAL CHARACTERIZATION TECHNIQUESchamber to find out the free volume. Mass of the sample (measured on a weighing balance)was entered in the machine’s software. Density was therefore calculated using the values ofmass and volume. A total of 10 cycles of purging and evacuation of helium gas wasperformed to obtain standard deviations.3.5.2. Nitrogen adsorptionThe samples were degassed at 300 °C under flowing N2 for a duration of 2 h prior toanalysis. About 100 mg of activated samples and 500 mg of chemically treated samples weretested in the BET analyzer. The weight of empty sample tubes and the weight of samples afterdegassing were used to calculate the amount of sample being tested.Figure 3.9 shows the degassing station (Micrometritics VacPrep 061), Tristar II Plusnitrogen adsorption analyzer and the TGA analysis of degassing leached CB in the TGAanalyzer. The degassing conditions were tested in the TGA equipment, wherein the samplewas heated to 300 °C with continuous flow of N2 gas. Since no weight loss was seen in thesample after 2 h (Figure 3.9c) of heating in N2, these conditions were chosen to be optimumfor degassing. BET surface area, free space, and pore size distribution were quantified bystudying N2 and He adsorption at different relative pressure values at room temperature and-196 °C. The total pore volume was defined by the volume of N2 molecule adsorbed at arelative pressure P/Po=0.95. The micropore volume was calculated using the t-plot method,with the slope of the curve between quantity adsorbed vs thickness for calculation ofmicropore volume.513.5. MATERIAL CHARACTERIZATION TECHNIQUESa bcFigure 3.9: Nitrogen adsorption equipment: a) Degassing station, b) Micromeritics® TristarPlus analyzer, and c) TGA analysis results for heating rCB sample from room temperatureto 300 °C under flowing nitrogen (degassing conditions).3.5.3. Elemental analysis by combustionElemental analysis was performed at the University of Essen with Eurovector CHNS-Oanalyzer EA300. In this analysis, carbon samples (<500 mg) were combusted at 1000 °C in523.5. MATERIAL CHARACTERIZATION TECHNIQUESO2, and the products were analyzed by gas chromatography. The gases formed due to thematerial’s combustion are CO2, H2O, N2, SO2 and O2, which were then detected to calculatetheir weight percentage.3.5.4. Electrical conductivity measurementsElectrical conductivity was calculated using powder resistivity measurement systemMCP-PD51 developed by Mitsubishi chemical analytech in Cologne, Germany. Theresistance was measured by the four-point probe method at varying loads. About 1 g ofsample was added to a cylindrical chamber of stainless steel and an external load wasapplied on the sample through punches. The load was applied mechanically using ahydraulic press and was varied from 1 kN to 10 kN. The resistance was measured throughthe circuit. Also the sample height was measured for the different loads. Resistivitymeasurements were then obtained using the Equation 3.1 [146]:R = ρl/A (3.1)Where R was the resistance, ρ was the resistivity, l and A were the height and crosssectional area of sample respectively. These resistivity values were used to calculate theelectrical conductivity of samples (by calculating the inverse) using the instrument software.3.5.5. X-ray diffractionX-Ray Diffraction (XRD) experiments were carried out at DLR in Cologne, Germany. TheXRD experiments were carried out using Bruker® D8 Advance A25 X-Ray Diffractometerwith Cu K-alpha radiation of wavelength 1.54 Å. Powder rCB samples were placed in a plasticsample holder and inserted in the XRDmachine’s sample rack. A step size of 0.02°with a timeper step of 10 °/s was used for all the scans. X’Pert HighScore software was used for all postanalysis data processing.533.5. MATERIAL CHARACTERIZATION TECHNIQUES3.5.6. Scanning electron microscopyA Tescan® Mira3 XMU field emission Scanning Electron Microscope with Oxford® AztecX-Max Energy Dispersive Spectroscopy (X-EDS) was used for chemical analysis. A scoop ofthe rCB sample was pasted on an Al stub with double-sided carbon tape. These stubs werethen inserted in the microscope for analysis. Electrodes before and after cycling were alsoattached to the Al stub with the double sided carbon tape. The Oxford® AZtec software wasused for all post characterization data processing.3.5.7. Transmission electron microscopyA Philips Tecnai F30 STEM (Figure 3.10) was used for TEM analysis which was performedin DLR, Cologne. Samples were prepared by mixing rCB samples with alcohol in a pestle andmortar. A dropper was used to suspend this slurry on a TEM support grid (Quantifoil R2/1carbon film on 200 mesh Cu grids; Quantifoil Micro Tools). The microscope was operated at300 keV equipped with a Gatan MSC 794 CCD-Camera and windowless EDAX Apollo XLTWSDD-detector for EDS analysis. The beam diameter was 10 nm.543.5. MATERIAL CHARACTERIZATION TECHNIQUESFigure 3.10: Transmission Electron Microscope (TEM) at DLR.3.5.8. FTIR analysisFTIR analysis was performed using Bruker Tensor 27 IR system at DLR Cologne.Chemically treated rCB samples were first mixed with KBr powder (IR inactive) in traceamounts. This mixture was ground and mixed using a pestle and mortar. After 15 mins ofmixing, the samples were inserted into a die, and the container was sealed with twopunches. A load of 10 kN was applied to the samples for 30 secs. After compaction of thepowder, the load was removed, and the pellet was carefully taken out of the die. The pelletwas dried in a vacuum oven at 30 mbar for 1 h to remove moisture adsorbed on the surface.FTIR analysis was then performed with 16 background and sample scans between 400 cm-1to 4000 cm-1. OPUS software was used for all post characterization data processing.553.5. MATERIAL CHARACTERIZATION TECHNIQUES3.5.9. FTIR gas analysisThe gas analysis was performed using TGA equipment coupled with FTIR spectroscopyunder Ar atmosphere (see Figure 3.11) at DLR Cologne. The TGA used was TG209 F1 Libraby Netzsch, coupled with Bruker Tensor 27 IR system. A sample of approximately 20 mgwas used for TGA experiments. The crucible used for the DSC/TGA measurements was anempty alumina crucible. The outlet hose was maintained at 200°C to avoid condensation ofexhaust gases. FTIR signal was obtained from the exhaust gases after every minute. Thissignal was analyzed using OPUS software to study the composition of exhaust gases atdifferent temperatures.Figure 3.11: Netzsch Instruments® TGA/FTIR equipment.3.5.10. Raman spectroscopyRaman spectroscopy was performed using a Renishaw in via raman microscope systemwith a 100× dry objective, 800 lines per mm diffraction grating, and 628 nmcontinuous-wave pump laser beam. Carbon powder was added to a quartz glass slide withthe help of a double sided tape and focused under the microscope before analysis. A laserpower of 50% was used for all experiments and WiRE software was used for baselinecorrection (Figure E.5). Peaks centered at 1340 cm-1 and 1580 cm-1 were used to calculate theID/IG ratio where ID and IG are the integrated intensities of D and G band, respectively.563.5. MATERIAL CHARACTERIZATION TECHNIQUESAlthough both peak area and peak intensity ratios were often used in the literature, peakintensities were suggested as more accurate due to possible inaccuracies in areameasurements performed during curve fitting [158]. Curve fitting was performed usingOrigin pro® software for peak analysis using a Lorentzian curve commonly used for fittingraman peaks for CB samples [159]. The microcrystalline planar crystal size (La) was alsocalculated using Equation 3.1 [159]:La = 44(ID/IG)-1 (3.2)3.5.11. Proximate analysis of rCBProximate analysis was performed for all rCB samples to determine their purity. Thismethod was based on ASTM D7582-15 to measure the purity of charcoal samples [160].Although the standard requires 1 g of sample, due to limitations in the TGA apparatus, only15 mg of the sample could be tested per run under N2 environment. The heating ratefollowed during the analysis was 25 °C/min, and the percentage weight of the sample wascomputed by using the loss in mass. Figure 3.12 shows the instrument schematic duringproximate analysis. Two identical alumina crucibles were loaded in the TGA unit onecontaining the sample and the other being empty (reference), as shown in Figure 3.12a. Thesamples were first heated up to 120 °C and held isothermally for 10 mins (Figure 3.12b) toevaluate the moisture content. The volatile composition was then found by heating thesample upto 950°C and keeping isothermally for 15 mins (Figure 3.12c). The chamber wasthen purged with O2 and the chamber had O2/N2 ratio of 1:1 for 100 mins in order to burnthe carbon in the samples and obtain the FC content (Figure 3.12d). The remaining mass inthe crucible was the ash present in the samples and could not be burnt by the presence ofO2. Hence the purity of samples was also measured using proximate analysis.573.5. MATERIAL CHARACTERIZATION TECHNIQUESFigure 3.12: Schematic of proximate analysis experiment perfromed in the TGA unit: a)Sample at room temperature (N2), b) Sample at 120 °C indicating moisture loss (N2), c)Sample at 950°C indicating volatile removal (N2), and d) Sample at 950°C indicating ash left(air). (pictures taken from BioRender.com)3.5.12. ICP-AES analysisICP-AES analysis was performed using ThermoFisher iCAP 6000 ICP-AES system onHCl and NaOH solutions after leaching was performed on raw carbon char, with differentparameters. The purpose of these experiments was to identify the elements present in theleached solution which were the impurities removed from raw carbon char. After collectingthe chemical solutions, they were diluted to 1 M in concentration for its use in theinstrument using RO water. The 5 M concentrated solution was diluted 5 times and the 10 Msolution was diluted 10 times with RO water. These diluted samples were then tested fortheir composition in the ICP-AES analyzer.583.6. NOMENCLATURE OF DIFFERENT CARBON MATERIALS3.6. Nomenclature of different carbon materialsSince several carbon materials were made in this research, the following nomenclaturewas developed:• Raw carbon char: As-received pyrolized carbon char from industry partner.• Acid treated raw carbon char: Carbon obtained after different acid treatmentsperformed on the raw carbon char.• Base treated raw carbon char: Carbon obtained after different base treatmentsperformed on raw carbon char.• Leached carbon black: 5 M HCl+ 10 M NaOH treated raw carbon char.• Leached carbon black+heat: leached CB with heat treatment at 950 °C for 1 h at 10°C/min.• KOH AC: KOH activated leached carbon black.• CO2 AC: CO2 activated leached carbon black.• rCB: General term for different grades of carbon black samples obtained from rawcarbon char after different treatments59Chapter 4: Results and Discussion:Chemical LeachingThis chapter presents the results obtained from the chemical leaching experiments andcharacterisation of the recovered carbon black grades. The results are organised into threesections as follows:• 4.1 Acid leaching of raw carbon char: The section summarizes the results of leachingexperiments using different acids.• 4.2 Base leaching of raw carbon char: The section summarizes the results of leachingexperiments using different bases.• 4.3 Combined acid and base leaching: The section summarizes the analysis of "leachedCB" sample made using combined acid (5 M HCl) and base (10 M NaOH) treatment.4.1. Acid leaching of raw carbon charAlthough several metallic impurities were detected in the raw carbon char in traceamounts, the three major contaminants were Zn, Si, and S (Table 3.1). Hence, the aim ofthese experiments was to explore the ideal acid, slurry ratio, molarity, and leaching time toremove these primary impurity elements.4.1.1. Optimization of type of acidAs discussed in Section 3.3.1, different acids were explored to leach inorganic impuritiesfrom the raw carbon char. The effect of acid leaching on the concentration of Zn, Si, and S604.1. ACID LEACHING OF RAW CARBON CHARwas evaluated using SEM-EDS analysis (Figure 4.1) and proximate analysis (Table 4.1).Additional results (from repeat experiments) from proximate analysis are included inAppendix A. Since the error in measurements (for proximate analysis experiments) was<0.5%, it was not necessary to repeat all sample measurements. As expected, the raw carbonchar had the lowest FC content and the highest ash content. This was also seen in Figure4.1, since most impurity elements (ash)/C were present in the raw carbon char. H2SO4 wasnot able to effectively remove most of the impurities from the raw carbon char as seen inFigure 4.1 and Table 4.1. Literature suggested that C obtained from H2SO4 treatment wasbound to an additional -COOH and -C=O group due to reaction with the acid [161]. Further,the use of H2SO4 acid possibly introduced S in to the rCB matrix (S/C ratio was >1.24%).Therefore, H2SO4 was not the best candidate for purification of raw carbon char.Figure 4.1: SEM-EDS analysis of impurities present in different grades of rCB obtained afteracid treatment on raw carbon char.614.1. ACID LEACHING OF RAW CARBON CHARHNO3 and HCl treatments resulted in similar purity of the leached rCB; however, it wasseen that 10MHCl yielded a lower concentration of S/C (0.94%)when compared to 10MHNO3(1.38%) treated samples. For both HCl and HNO3 treated raw carbon char, the FC content wasgreater than 86% from proximate analysis experiments. HCl has a higher dissociation constant(ka=107) than HNO3 (ka=200) resulting in easier removal of inorganic species by replacingH+ ions with metal cations [76, 162]. Similar to these results, literature suggested that HCl(ash=9.49%) was the most effective in demineralization of tire-derived rCB in comparison toHNO3 (ash=9.86%) and H2SO4 (ash=10.30%) [78]. Therefore, HCl was seen to be the mostappropriate acid for the treatment of the raw carbon char.Table 4.1: TGA proximate analysis results of acid treated raw carbon char.Sample Ash (%) Volatiles (%) Moisture (%) FC (%)Raw carbon char 12.09 5.69 0.98 81.245 M H2SO4 5.28 4.83 0.82 89.0710 M H2SO4 5.05 4.74 0.96 89.255 M HCl 5.07 4.49 0.79 89.6310 M HCl 4.94 4.14 1.18 89.745 M HNO3 4.95 5.72 1.34 87.9910 M HNO3 4.90 6.52 1.64 86.94The skeletal density had a direct correlation with the purity of the samples. The resultsfrom skeletal density measurements are included in Table 4.2. Since the raw carbon char hadthe highest concentration of impurity elements (See Figure 4.1 and Table 4.1), the density ofthis sample was the highest. The density of the samples treated with both HCl and HNO3were the lowest indicating the highest purity (i.e., lowest contamination) in these samples.The density of 10 M HCl treated sample was an outlier (with density >0.0097 g/cm3 than5 M HCl treated sample). This was likely due to variations in sample homogeneity whilemeasurements were taken. Also, the density of commercial CB was found to be within therange seen for these samples varying from 1.8 g/cm3 to 2.1 g/cm3 [163].624.1. ACID LEACHING OF RAW CARBON CHARTable 4.2: Skeletal density measurements of acid treated raw carbon char.Sample Density (g/cm3) Standard deviation (g/cm3)Raw carbon char 1.9218 0.00095 M H2SO4 1.8587 0.001910 M H2SO4 1.8546 0.00095 M HCl 1.8167 0.000810 M HCl 1.8264 0.00125 M HNO3 1.8485 0.001810 M HNO3 1.8285 0.00224.1.2. Optimization of molarity of acidFigure 4.2 shows the effect of HCl concentration on the removal of impurities from theraw carbon char. Zn was still present after treatment with 1 M HCl, hence a higherconcentration was required for its removal (Figure 4.2b). The Zn content of 10 M HCl and 5M HCl leached rCB samples was ∼0 %, whereas the S/C content was 0.76% and 0.98%,respectively. Si could not be completely removed from the samples even after treatmentwith 10 M HCl. These results were corroborated by the ICP results (Figure 4.2a) whichshowed increased concentration of Zn in the leached HCl solution with increase in the acidconcentration. The Zn content in the solution was more than four times higher (>1500 ppm)for the sample treated with 5 M HCl solution with respect to 1 M HCl solution. From bothICP and SEM-EDS results, it was concluded that the purity of samples treated with 5 M HCland 10 M HCl was similar (0% of Zn/C, <500 ppm of Zn). Similar results were reported in theliterature when only minor differences in the ash (a difference of <0.3 wt% ash)concentration was observed by increasing the normality of H2SO4 from 1 N to 10 N for thedemineralization of tire-derived rCB [164]. Similarly, the treatment of tire-derived char withHCl reduced the ash content (from 6.1% to 5.6%) with increase in molarity from 2 M to 8 M,however, the optimal concentration of HCl was determined to be 4 M, since there was littleor no improvement in purity with further increase in acid molarity [153]. Therefore,considering the past literature, and current experimental results, 5 M HCl was seen to be the634.1. ACID LEACHING OF RAW CARBON CHARmost appropriate molarity for acid treatment.abFigure 4.2: Effect of acid concentration on purity of rCB: a) ICP analysis of acid solutionsobtained after leaching experiments were complete, and b) SEM-EDS analysis of differentgrades of rCB obtained.4.1.3. Optimization of slurry ratioFigure 4.3 shows the effect of changing the acid slurry ratio on the removal of impuritiesfrom the raw carbon char. As seen in Figure 4.3a, the Zn concentration in the leached HClsolution increased until a slurry ratio of 50 g/L was used. This indicated an improvement in644.1. ACID LEACHING OF RAW CARBON CHARZn removal with the increase in slurry ratio.abFigure 4.3: Effect of acid slurry ratio (g/L) on purity of rCB: a) ICP analysis of acid solutionsobtained after leaching experiments were complete, and b) SEM-EDS analysis of differentgrades of rCB obtained.SEM-EDS results (Figure 4.3b) indicated the presence of trace amounts of Zn in thesamples. This Zn/C content increased with the increase in the slurry ratio. However, thedifference in the values was negligible (<0.16%). This was also seen in literature where aplateau was reached (for maximum removal of ash). The studies revealed that a slurry ratioof 333.3 g/L for 1 N H2SO4, and 200 g/L of 4 M HCl solutions were optimum for maximum654.1. ACID LEACHING OF RAW CARBON CHARash removal [153, 164]. It was suggested that an increase in slurry ratio after a certain limitdid not facilitate additional leaching because of limited availability of chemical species forreaction with the rCB matrix. Therefore, considering past literature and ICP results, a slurryratio of 50 g/L was chosen to be optimum for acid leaching experiments in the present work.4.1.4. Optimization of leaching timeFigure 4.4 shows the effect of HCl leaching time on the removal of impurities from theraw carbon char. It was seen that within 2 h of leaching, Zn was completely removed fromthe rCB sample (Figure 4.4b). Literature revealed a reduction in ash with increase in leachingtime up to 1 h for HCl leaching of tire-derived rCB samples, therefore a minimum of 2 h wereemployed for leaching [153]. In the present work, the variation of Zn content in the leachedHCl solution was <500 ppm with increase in leaching time, thus implying 2 h being sufficientfor Zn removal. This was observed due to decrease in solvent strength after 2 h of leachingtime and decrease in contact area between impurities and the chemical [76]. The Si and Scontent was not significantly affected by the variation in leaching time as seen in the Figure4.4.664.2. BASE LEACHING OF RAW CARBON CHARabFigure 4.4: Effect of acid leaching time on purity of rCB: a) ICP analysis of acid solutionsobtained after leaching experiments were complete, and b) SEM-EDS analysis of differentgrades of rCB obtained.4.2. Base leaching of raw carbon charAlthoughmostmetallic impurities were successfully removed byHCl treatment of the rawcarbon char, SiO2 still remained in the acid leached samples. Literature suggested that Si couldbe removed using base leaching [153, 164]. Therefore, the goal of the following experimentswas to remove SiO2 from the samples.674.2. BASE LEACHING OF RAW CARBON CHAR4.2.1. Optimization of type of baseFigure 4.5 and Table 4.3 includes the chemical composition of the samples after basetreatment obtained by SEM-EDS analysis and proximate analysis, respectively. Only majorimpurity elements (Zn, Si, and S)/C% detected from EDS analysis were included in Figure4.5. One sample was also repeated for testing in the TGA equipment (Appendix A) and theerror in measurement from proximate analysis was <0.5%.It was seen that 10 M KOH treatment was effective in reducing the Zn and S content tothe highest degree (Zn/C=2.18%, S/C=1.43%), but the ash content in the sample was thehighest (9.65%), indicating the presence of other impurities. These impurities includedinorganic impurities in the raw carbon char along with insoluble alkali complexes, zeolite,and sodalite formed due to high reactivity of KOH [165]. KOH was more effective inremoving S from coal samples when compared to NaOH because of this high reactivity asseen in the literature[166]. However in this work, >1.43% S/C and >2.18% Zn/C remained inthe samples after KOH treatment. Thus, KOH was not effective in removing Si. Since acidtreatment of the raw carbon char was already successful in removal of Zn and other metallicimpurities, KOH was not the optimum choice for base treatment of raw carbon char. NaOHtreatment on the other hand resulted in a more effective removal of the Si impurity (<0.34%Si/C), which was also seen in literature for tire-derived rCB treatment [161].684.2. BASE LEACHING OF RAW CARBON CHARFigure 4.5: SEM-EDS analysis of impurities present in different grades of rCB obtained afterbase treatment of raw carbon char.Table 4.3: TGA proximate analysis results of base treated raw carbon char.Sample Ash (%) Volatiles (%) Moisture (%) FC (%)Raw carbon char 12.09 5.69 0.98 81.245 M KOH 9.08 6.02 0.94 83.9610 M KOH 9.65 5.18 0.85 84.325 M NaOH 9.39 5.74 0.66 84.2110 M NaOH 8.10 4.96 0.24 86.70Skeletal density measurements from base treated raw carbon char samples are includedin Table 4.4. As expected from SEM and TGA results, the sample treated with 10 M NaOHhad the lowest density indicating minimum impurity content. Also, the density results forall base treated samples were lower than that of raw carbon char, indicating partial removalof certain elements from the raw carbon char with base treatments. This was seen by thereduction in concentration of Zn, Si and S (Figure 4.5) by varying degrees but not their694.2. BASE LEACHING OF RAW CARBON CHARcomplete removal. By studying the properties of samples produced by different basetreatments, NaOH was chosen for further studies because of its ability to remove SiO2.Table 4.4: Skeletal density measurements of base treated raw carbon char.Sample Density (g/cm3) Standard deviation (g/cm3)Raw carbon char 1.9218 0.00095 M KOH 1.9143 0.001810 M KOH 1.9123 0.00155 M NaOH 1.9070 0.009710 M NaOH 1.9051 0.00114.2.2. Optimization of molarity of baseFigure 4.6 shows the effect of NaOH concentration on the purity of rCB samples. As seenin Figure 4.6a, the Si content in the solution increased considerably (10 times, >500 ppm) inthe 10 M NaOH solution compared to the 5 M NaOH. Also, there was a difference in the Sicontent from SEM-EDS results of samples without normalization (Figure A.2) of 5 M NaOH(0.75±0.08 wt%) and 10 M NaOH (0.29±0.03 wt%) treated raw carbon char. The Si/C contentwas also lower for 10 M NaOH treated sample when compared to lower acid molarities, asseen in Figure 4.6b. From proximate analysis results (Table 4.3), 10 M NaOH treated rawcarbon char had the minimum ash content indicating maximum purity. Literature revealedsimilar results showing reduced ash concentration of tire-derived rCB with increase in NaOHconcentration [78, 164].704.2. BASE LEACHING OF RAW CARBON CHARabFigure 4.6: Effect of base concentration on purity of rCB: a) ICP analysis of base solutionsobtained after leaching experiments were complete, and b) SEM-EDS analysis of differentgrades of rCB obtained.4.2.3. Optimization of slurry ratioFigure 4.7 shows the effect of the slurry ratio on the purity of the rCB samples. Similarto results from acid treatment (Section 4.1.3), a slurry ratio of 50 g/L resulted in a maximumSi concentration in the electrolyte as seen in the ICP results (Figure 4.7a). A significantdifference was not seen in the SEM-EDS results (Figure 4.7b) due to low concentration of Si714.2. BASE LEACHING OF RAW CARBON CHARin the samples after NaOH leaching experiments.abFigure 4.7: Effect of base slurry ratio (g/L) on purity of rCB: a) ICP analysis of base solutionsobtained after leaching experiments were complete, and b) SEM-EDS analysis of differentgrades of rCB obtained.4.2.4. Optimization of leaching timeFigure 4.8 shows the effect of leaching time during NaOH treatment of the raw carbonchar. Although ICP results (Figure 4.8a) showed an increase in the Si content in the leachsolution, this increase was not considerable (<200 ppm). Also, SEM EDS results (Figure 4.8b)724.2. BASE LEACHING OF RAW CARBON CHARindicated a minimum difference in the Si concentration between the different samples, due tothe low concentration of Si/C in the rCB matrix. Therefore, it was concluded that a leachingtime of two hours was sufficient, due to the reduced strength of the base as a result of reactionwith Si [76].abFigure 4.8: Effect of base leaching time on purity of rCB: a) ICP analysis of base solutionsobtained after leaching experiments were complete, and b) SEM-EDS analysis of differentgrades of rCB obtained.734.3. COMBINED ACID AND BASE LEACHING4.3. Combined acid and base leaching"Leached CB" was produced by combined HCl and NaOH treatment of raw carbon charand was used as the raw material for all subsequent experiments. This section includes adetailed comparison between raw carbon char and the "leached CB" samples.4.3.1. Physical analysisFigure 4.9 shows the SEM images of the leached CB. It was found that agglomerates aslarge as 100 µm were present in the sample. This was due to air drying of samples postchemical treatments, resulting in weakly bound agglomerates. Also, the agglomerate sizevaried considerably (20-100 µm), due to weakly bound aggregate structures consisting ofdifferent grades of CB used for the initial tire manufacturing, as seen in the SEM image[153].The white areas in the Figure 4.9 were Si rich phases segregated in the rCB matrix (refer toSection 4.3.2). The skeletal density value for leached CB was minimum (1.7585±0.0059g/cm3) when compared to all rCB grades prepared by chemical leaching (Table 4.2 and Table4.4). These results were in agreement with the high purity levels of leached CB sample(Section 4.3.2).744.3. COMBINED ACID AND BASE LEACHINGa bFigure 4.9: SEM (BSE) analysis of leached carbon black: a) At 200x, and b) At 500x.Figure 4.10 shows the structure of raw carbon char and leached CB using TEM analysis.As seen in Figure 4.10a and b, both raw carbon char and leached CB had a grape like structurecommon for rCB from tires [153, 167]. The primary particles in both cases were ∼20 nm indiameter. As seen in Figure 4.10d, the amorphous structure of leached CBwas visible at highermagnification, showing randomly oriented graphene like sheets. The porosity of leached CBand raw carbon char samples was analyzed by N2 adsorption experiments. The change inSBET was negligible between raw carbon char (62 m2/g) and leached CB (68 m2/g) due to lackof thermal treatments or activation [153].754.3. COMBINED ACID AND BASE LEACHINGa bc dFigure 4.10: TEM images of: a) Raw CB, and b-d) Leached CB.Considering the use of the rCB was intended for energy storage applications, some otherproperties like graphitization and electrical conductivity were also analyzed. Figure 4.11shows the electrical conductivity and Raman analysis of the rCB samples.764.3. COMBINED ACID AND BASE LEACHINGabFigure 4.11: Electrical analysis of rCB samples: a) Effect of applied pressure on electricalconductivity, and b) Raman spectroscopy of rCB samples.As seen in Figure 4.11a, the electrical conductivity of all samples increased with anincrease in applied pressure. This was due to better contact between rCB particles onapplication of pressure. Also, the electrical conductivity of leached CB at higher pressurewas greater than raw carbon char due to removal of insulating impurities present in the rawcarbon char as seen from SEM-EDS analysis. It should be noted that since no heat treatmentwas applied to these samples, the difference between the structures of leached CB and raw774.3. COMBINED ACID AND BASE LEACHINGcarbon char was limited merely due to removal of inorganic impurities and not due tographitization, which was expected to proceed at temperatures >600 °C [37]. This was seenby the proximity of the ID/IG values of raw carbon char (1.09) and leached CB (1.08) as seenin Figure 4.11b. Similarly, the La values were similar; 4.02 nm and 4.62 nm for raw andleached CB respectively because of lack of thermal treatments.4.3.2. Chemical analysisSEM-EDS analysis of leached CB revealed the presence of S (0.89 wt%) and traces of Zn(0.02 wt%) and Si (0.57 wt%) in the sample. Si was seen to segregate as separate phases (whiteregions) in the leached CB as seen in Figure 4.9. Table 4.5 shows the TGA proximate analysisresults from leached CB. It was seen that the ash content in the raw carbon char reduceddrastically (from 12.09% to 1.51%) after the chemical treatments. As seen from the SEM results,these impurity elements included mainly Zn and Si containing impurities. S could not besuccessfully removed from the samples by chemical leaching. The only contaminants stillseen in the samples were therefore the volatiles (∼6%) or most likely S containing species.Table 4.5: TGA proximate analysis results of leached carbon black.Sample Ash (%) Volatiles (%) Moisture (%) FC (%)Raw carbon char 12.09 5.69 0.98 81.24Leached CB 1.51 6.68 1.08 90.73TEM-EDS analysis was also performed on raw carbon char and leached CB samples(Figure 4.12) to identify the phases present in the samples. TEM mapping analysis of rawcarbon char revealed the presence of Zn together with S indicating the presence of ZnSphase. ZnS was known to be formed in tire-derived rCB samples on reaction between ZnOand S present in tire rubber during pyrolysis [168]. This phase was not detected in leachedCB samples in both SEM and TEM-EDS analysis due to its effective removal.784.3. COMBINED ACID AND BASE LEACHINGa bcdFigure 4.12: TEM-EDS mapping results of raw CB: a) TEM image of analyzed area, b)Layered image (C=red, ZnS=blue, SiC=yellow, SiO=green, unallocated=grey), c) Zn map,and d) S map.794.3. COMBINED ACID AND BASE LEACHINGThe elemental maps of other elements detected in the TEM analysis are included inAppendix A (Figure A.3). SiO2 and SiC phases were also detected in the raw carbon charsamples, as was also reported in the literature for tire-derived char [169]. The presence ofZnS and SiC was further verified by the XRD analysis (Figure 4.13a). SiO2 peak had a lowintensity in the XRD scans possibly due to its low concentration in the samples. Aninteresting difference between the raw carbon char and the leached CB was an intense peakat 2θ of ∼26◦ which was indexed as a graphite peak [170, 171]. This was likely also presentin the raw carbon char but was not visible because of the presence of other impurities in theraw carbon char matrix.Demineralization resulted in rCBwith functional groups attached to the rCBmatrix [153].FTIR spectroscopywas therefore performed to identify the surface functional groups attachedto the rCB matrix. The results from FTIR spectroscopy are included in Figure 4.13b. Both rawcarbon char and leached CB had OH functional groups attached, which indicated a possibilityof adsorbed moisture on their surface [172]. Also, minor peaks were seen at 1475 cm-1 and1500 cm-1, indicating the presence of aromatic functional groups [173, 174]. These groupswere likely a contributing factor to the volatiles detected from proximate analysis (Table 4.5).The broad peak at 1111 cm-1 represented C-O oxygenated functional groups indicating thepresence of carboxylic acid, ether and ether functional groups [175]. The minor peak at 1444cm-1 indicated the presence of S=O [175]. C-H stretching bonds were present also present at2800 cm-1 and 2900 cm-1 [172, 174]. This indicated the presence of non-aromatic alkenes (Hring attached to styrene group) in these samples [176]. As expected, the raw carbon char hadSi-O functional group present [177]. This was because of the presence of SiO2 impurity whichwas also seen in the SEM-EDS results (See Figure 4.9).804.3. COMBINED ACID AND BASE LEACHINGabFigure 4.13: Chemical analysis of leached and raw carbon char: a) XRD analysis, and b)FTIR spectroscopy of rCB.Despite having a better idea of what compounds the carbon materials are bound to, noneof these analysis methods are dependable for identifying the concentration of lower atomicnumber elements like C, O, H, S, and N. Therefore, elemental analysis was performed on theleached CB sample. The results from elemental analysis are included in Table 4.6.814.4. SUMMARYTable 4.6: Elemental analysis results of leached carbon black.Sample Carbon(wt%)Hydrogen(wt%)Nitrogen(wt%)Sulphur(wt%)Oxygen(wt%)Ash(wt%)Raw carbon char 82.1 1.01 0.48 3.53 4.76 8.11Leached CB 92.6 1.34 - 0.65 4.26 1.14As seen in Table 4.6, the carbon content was higher for the leached CB when comparedto raw carbon char, which was expected from the chemical treatments performed. S contentin leached CB was reduced due to chemical treatments and possible removal as H2S, howevertrace amount of S (0.657 wt%) remained. It was interesting to note that the O concentrationof carbon material was not affected significantly by chemical treatments. Trace of N2 wasdetected in the raw carbon char likely because of pyrolysis in N2 containing atmospheres.The remaining impurities that were not detected by the analyzer were termed as ash. Mostlikely this ash in leached CB was SiO2 or SiC compounds as found in EDS and XRD results.4.4. SummaryIn this chapter, the optimization of leaching experiments was performed. Treatment ofraw carbon charwith 5MHCl and 10MNaOHwas found to be optimum for impurity removal.The "leached CB" sample was prepared by subsequent treatments of 5 M HCl and 10 M NaOHon raw carbon char for a leaching time of 2 h and slurry ratio of 50 g/L. This leached CB samplehad a higher C content (92.6 wt% from Table 4.6), higher electrical conductivity (Figure 4.11),and lower ash content (1.51% from Table 4.5) when compared to the raw carbon char. Theonly limitation with the use of leached CB samples was the low improvement of SBET (from62 m2/g to 68 m2/g) and presence of volatiles (∼6% from Table 4.5). Therefore, activationand heat treatment experiments were performed on the leached CB sample. These results areincluded in the next chapter.82Chapter 5: Results and Discussion:Activation and Devolatilization ofLeached CBThis chapter presents the results obtained from the heat treatment experiments andcharacterisation of heat treated leached CB. The results are organised into two broad categories:activation and devolatilization of leached CB.5.1. Activation of leached CBThe leached CB was activated by two distinct paths to yield a product termed activatedcarbon (AC). Thermal activationwith CO2, and chemical activationwith KOHwere examined.The results are included in the following sections.5.1.1. Carbon dioxide activationFigure 5.1 shows the effect of the activation temperature and activation time on the SBETand micropore volume (Vmi) of AC obtained via CO2 activation. Literature reviews suggestedthat changing the flow rate and char weight had no effect on char activation, therefore theseparameters were not varied in the present research [178]. As seen in the Figure 5.1, the SBETincreased with an increase in the activation temperature and time, due to greater diffusion ofCO2, as reported in literature [179]. The sample subjected to 3 h of activation treatment (at 900°C), had a slightly lower SBET and Vmi values (<80m2/g), however this differencewaswithin themeasurement error and therefore it was concluded that activation for both 2 and 3 h resulted835.1. ACTIVATION OF LEACHED CBin leached CB activation. Thermal cracking and oxidation of volatiles were expected at highertemperatures (>900 °C) causing additional pore formation at 1000 °C [55]. This was due to theextra energy provided for the activation reaction (between CO2 and char) resulting in theformation of new pores [49]. The Vmi however (Figure 5.1a), decreased with an increase inthe temperature from 900 °C to 1000 °C likely due to uncontrolled pore expansion and collapseof walls between pores, as reported extensively in the literature [57, 60, 74, 175, 179].abFigure 5.1: SBET and Vmi of leached CB activated with CO2: a) Effect of temperature, and b)Effect of time.The information on the adsorption capacity and pore structure of the ACs (measured byN2 adsorption) is included in Figure 5.2 and Table 5.1.845.1. ACTIVATION OF LEACHED CBabFigure 5.2: BET analysis of CO2 activated rCB: a) Adsorption isotherm, and b) Pore sizedistribution of CO2 activated samples.As seen in Figure 5.2a, N2 adsorption began at low relative pressure (<0.1) for samplewith an activation temperature of more than 900 °C. This indicated the presence ofmicroporosity in the samples which was consistent with the pore size distribution curves(Figure 5.2b) [180]. The adsorption isotherm for CO2 AC samples (with activationtemperature >900 °C) was categorized as Type IV according to the International Union ofPure and Applied Chemistry (IUPAC) classification system [181]. This isotherm was855.1. ACTIVATION OF LEACHED CBassociated with a hysteresis loop characteristic of mesoporous materials in the high relativepressure range (0.7-1) commonly found for tire-derived ACs [179]. It was observed that thehysteresis loop was present for samples activated at higher temperatures (>900 °C)indicating increased mesoporosity in the samples. The increased mesoporosity could also beseen in Figure 5.1b. However, for samples activated at lower temperatures (<900 °C) anintermediate between Type I and II isotherm was seen as a result of limited mesopores inthe sample structure [77, 181]. Both the micropore volume and total pore volumes increasedwith an increase in time (Table 5.1 and Figure 5.1) likely due to favourable activationconditions (increased time for effective contact and reaction with CO2 and char). Theburnoff values included in Appendix B (Table B.1) also increased with increased porevolume indicating the removal of C atoms. This result was consistent with literature [179].Table 5.1: N2 adsorption results from CO2 activation of leached CB.Sample(temperature-time)SBET(m2/g)Total porevolume(cm3/g)Microporevolume(cm3/g)CO2AC (800-3) 90.73 0.14 0.006CO2AC (900-1) 136.89 0.18 0.020CO2AC (900-2) 332.00 0.28 0.079CO2AC (900-3) 285.41 0.27 0.064CO2AC (900-6) 495.00 0.36 0.090CO2AC (1000-3) 803.74 0.59 0.018The maximum SBET value of 803 m2/g was obtained from CO2 activation at 1000 °C withan activation time of 3 h. However, it was observed that this sample had increased fractionof mesopores and micropores (Figure 5.2b). This indicated possible pore enlargement andcollapse of micropores with improved activation kinetics (higher temperature) [178].Proximate analysis was conducted on this sample, and revealed a volatile content of 0.95%,ash content of 3.96%, and FC content of 94.66%. The skeletal density of this sample was1.9839±0.0235 g/cm3 which was higher than leached CB (1.7585±0.0059 g/cm3). This waslikely because of higher ash content of the CO2AC (1000-3) sample as seen from the865.1. ACTIVATION OF LEACHED CBproximate analysis results. The activation experiments resulted in the partial removal ofvolatiles when compared to leached CB (where volatiles were at 6.68%) due to the hightemperature exposure. The ash content of the sample, however, was higher than in theleached CB sample, due to removal of C atoms during the activation process duringdevolatilization. It was reported that the presence of inert ash (SiO2 and Al2O3) deactivatedthe activation process in the presence of CO2 [169, 179]. The deactivation reactions limiteddiffusion of CO2 for tire, coal, and biomass samples [179, 182]. This was the possible reasonfor the low SBET values in leached CB samples activated with CO2. Since there was aconsiderable difference between the SBET values of the CO2AC (1000-3) sample and the otherCO2AC samples, the CO2AC (1000-3) sample was chosen for further analysis.Figure 5.3 shows the SEM images of CO2AC (1000-3) sample. As seen in Figure 5.3a, theagglomerate size of AC was not uniform and varied from 1 to 100 µm. At a highermagnification of 15 Kx, the porosity in the samples was clearly visible. Also, SEM-EDSanalysis revealed traces of both Si (0.21±0.00 wt%) and S (0.73±0.04 wt%) in the AC samples.The S and Si most likely comprised the remaining 0.95% volatiles and 3.96% ash detected inthe proximate analysis experiments.a bFigure 5.3: SEM images of the CO2AC (1000-3) sample: a) At 1kx, and b) At 15kx.875.1. ACTIVATION OF LEACHED CBFigure 5.4 shows the FTIR analysis of the CO2AC (1000-3) sample. It was found that theCO2 sample had no functional groups attached to the C matrix apart from the C=C bond(Figure 5.4b). This further indicated the removal of most volatiles from the C matrix. TheC=C bond was likely the remaining impurities attached to the AC matrix.Figure 5.4: FTIR analysis of CO2AC (1000-3) sample.Figure 5.5 and Table 5.2 include the analysis from Raman spectroscopy measurements.The ID/IG ratio was lower for the CO2AC (1000-3) sample (0.84) when compared to leachedCB (1.08) indicating reduced disorder characteristics in the activated sample as also seen inliterature [183]. This reduction in disorder was a result of removal of the functional groups(Figure 5.4) resulting in improved contact between the micro-graphitic layers. The ID/IG ratioof Super-P CB was 0.86 (Figure B.1 in Appendix B) and therefore the CO2AC (1000-3) samplewas expected to have a similar degree of graphitization like Super-P. La of the CO2AC(1000-3) sample (diameter of crystallite) increased (5.19 nm) when compared to leached CB(4.06 nm) due to removal of volatile compounds as will be seen in FTIR analysis of activatedsamples. This result suggests the effective removal of functional groups attached to the ACmatrix (Figure 5.4)[184]. Considering high SBET and low volatile content of the CO2AC(1000-3) sample, it was selected for electrochemical testing in Li-ion systems.885.1. ACTIVATION OF LEACHED CBFigure 5.5: Raman spectrocopy and curve fitting results for CO2AC (1000-3) sample.Table 5.2: Raman spectroscopy results for CO2AC (1000-3).Leached CB CO2AC (1000-3) Super-PR2 0.902 0.970 0.966D band (cm-1) 1337.68 1326.70 1338.96Intensity (a.u.) 0.32 0.79 0.76G band (cm-1) 1580.29 1582.76 1590.06Intensity (a.u.) 0.29 0.94 0.88ID/IG 1.08 0.84 0.86La (nm) 4.06 5.19 5.745.1.2. Potassium hydroxide activationFigure 5.6 shows the effect of activation temperature, time, and KOH impregnation ratioon the SBET and Vmi values of AC obtained from KOH activation. As seen in Figure 5.6a andb, the SBET was directly proportional to the activation temperature and time which wasconsistent with literature [45]. This increase in the SBET was limited for low activationtemperatures (<800 °C). It was suggested that for lower activation temperatures, ash presentin the samples resulted in the formation of complexes containing Si (i.e. KAlSi2, K2MgSi4)limiting SBET of biomass and coal samples [182].895.1. ACTIVATION OF LEACHED CBabcFigure 5.6: SBET and Vmi of leached CB activated with KOH: a) Effect of temperature, b)Effect of time, and c) Effect of impregnation ratio.905.1. ACTIVATION OF LEACHED CBAs seen in Figure 5.6a and b, the micropore volume decreased with a prolonged activationtime and a higher temperature. This was expected due to excessive pore widening during theactivation process. Figure 5.6c revealed that an impregnation ratio of four was optimum foractivation experiments, since higher ratios resulted in reduced SBET and pore volume. Thiswas also suggested in literature for activation of tire-derived rCB due to uncontrolled burningof the samples with higher impregnation ratios [77]. Figure 5.7 shows the adsorption isothermand pore size distribution of KOHAC samples.abFigure 5.7: BET analysis of KOH activated rCB: a) Adsorption isotherm, and b) Pore sizedistribution.915.1. ACTIVATION OF LEACHED CBAs seen in Figure 5.7, hysteresis was seen in all the samples with characteristics similarto Type IV isotherm according to the IUPAC classification system [181]. The hysteresis wasmore predominant for sample activated at higher temperature (>800 °C) and longeractivation times (>2 h) indicating pore enlargement. Table 5.3 includes all informationrelated to N2 adsorption of KOHAC samples. The sample KOHAC (900-3-4) revealed mainlymesopores with only slight improvement in SBET from sample KOHAC (900-2-4) with adifference of 25 m2/g (Table 5.3) as a result of micropore enlargement. Figure 5.7b revealedformation of micropores for samples with impregnation ratio of at least 4, for lower values,Vmi was extremely low, whereas for an impregnation ratio of 5, mesopore volume increaseddrastically. This was also seen in literature, where reduced yield and enlargement of poreswith impregnation ratio was reported for ratios >4 [185]. The burnoff values are included inAppendix B (Table B.1), which had a direct proportionality with the SBET of the samples.Due to limited macroporosity in KOHAC samples, these samples had lower burnoff valuesthan CO2AC samples. Since micropores were preferred for improved reaction kinetics inLi-ion cells (improved capacity, reduced irreversible capacity loss), the KOHAC (900-2-4)sample was selected for further analysis.Table 5.3: N2 adsorption results from KOHAC samples.Sample SBET(m2/g)Total porevolume(cm3/g)Microporevolume(cm3/g)KOHAC (700-2-4) 765.18 0.56 0.068KOHAC (800-2-4) 820.26 0.64 0.100KOHAC (900-1-4) 927.59 0.76 0.001KOHAC (900-2-1) 329.58 0.36 0.000KOHAC (900-2-2) 810.42 0.64 0.042KOHAC (900-2-4) 965.27 0.85 0.052KOHAC (900-3-4) 994.64 0.78 0.008KOHAC (900-2-5) 731.82 0.68 0.019The SBET obtained from KOH (900-2-4) sample was 965 m2/g. Proximate analysis wasconducted on this sample and revealed a volatile content of 4.92%, ash content of 3.6%, and925.1. ACTIVATION OF LEACHED CBFC content of 88.16%. The high volatile content indicated possible aromatics attached to theC-matrix which was also seen by C-H and O-H vibrations in the FTIR results (Figure 5.9b).The skeletal density of this sample was 1.8477±0.0178 g/cm3, which was slightly higher thanleached CB (1.7585±0.0059 g/cm3). This was likely because of higher ash and volatile contentof the KOHAC (900-2-4) samples as seen from the proximate analysis results. Figure 5.8 showsthe SEM and TEM images of the KOHAC (900-2-4) sample.a bc dFigure 5.8: SEM images of the KOHAC (900-2-4) sample: a) At 1 Kx, b) At 15Kx, and TEMimages c) At low magnification, and d) At high magnification.935.1. ACTIVATION OF LEACHED CBAs seen in Figure 5.8a, the agglomerate size of KOHAC (900-2-4) sample was smaller thanthat of CO2AC (1000-3) sample (Figure 5.3a). This was due to premixing of KOH and leachedCB using a pestle and mortar before activation which was not performed for CO2AC samples.Figure 5.8b shows the pores on the surface of the sample. SEM-EDS analysis revealed a lowerconcentration of Si (0.15±0.01 wt%) and S (0.26±0.03 wt%) when compared to the CO2AC(1000-3) sample. However, the volatile content was still higher than CO2AC (1000-3) sampledue to the lower temperature employed for the activation experiments. This likely resulted inthe presence of some aromatic compounds attached to the matrix as confirmed by O-H and C-H functional groups in the FTIR analysis (Figure 5.9b). The primary particles had a diameterof∼20 nm, which was similar to leached CB. As seen in Figure 5.8d, the primary particles hada turbostratic structure likely formed because of the heat treatment during activation process[37].Figure 5.9 shows the electrical conductivity and FTIR analysis results of the KOHAC (900-2-4) with respect to the leached CB sample. As seen in Figure 5.9a, the electrical conductivityof KOHAC (900-2-4) sample was five times higher than leached CB even at a load of 1 kN.This was attributed to the turbostratic nature of the AC sample implying partial graphitization(also seen in Figure 5.10) and removal of Si and S from the leached CB matrix. FTIR analysisas shown in Figure 5.9b revealed the presence of C-H vibrations indicating the presence ofaromatic rings (volatiles as also reported by [91]) in the samples as also seen in the proximateanalysis results. Raman spectroscopy was also performed on this sample to study possiblegraphitization of the KOHAC (900-2-4) sample.945.1. ACTIVATION OF LEACHED CBabFigure 5.9: Analysis of KOHAC (900-2-4) samples: a) Effect of applied pressure on electricalconductivity, and b) FTIR analysis of rCB.Figure 5.10 and Table 5.4 include the Raman spectroscopy analysis results of the KOHAC(900-2-4) sample. Figure 5.10 revealed a slight reduction in the ID/IG ratio when compared toleached CB sample. This indicated improved graphitic character of the sample [99]. Since theID/IG was lower than in the leached CB sample, the crystallite size of KOHAC (900-2-4) wasbigger for the KOHAC (900-2-4) sample. This may also be attributed to the intercalation andsubsequent removal of K in the CB lattice during treatment as suggested in literature [77].955.2. DEVOLATILIZATION OF LEACHED CBFigure 5.10: Raman spectroscopy results for KOHAC (900-2-4) sample.Considering the high pore volume, SBET and electrical conductivity of the KOHAC (900-2-4),this sample was selected for electrochemical testing in the Li-ion system.Table 5.4: Raman spectroscopy results for KOHAC (900-2-4).Leached CB KOHAC (900-2-4) Super-PR2 0.902 0.974 0.966D band position(cm-1) 1337.68 1339.02 1338.96Intensity (a.u.) 0.32 0.78 0.76G band position(cm-1) 1580.29 1576.13 1590.06Intensity (a.u.) 0.29 0.84 0.88ID/IG 1.08 0.92 0.86La (nm) 4.06 4.77 5.745.2. Devolatilization of leached CBAnother set of experiments were conducted to decrease the volatile content of the rCBsamples without affecting its SBET drastically. These experiments were termed as"devolatilization" experiments and the effect of heat treatment temperature, time andheating rate was studied on devolatilization of leached CB samples. A discussion on965.2. DEVOLATILIZATION OF LEACHED CBdifferent gases involving and reactions during the heating process of rCB is discussed indetail in Section 5.2.4.5.2.1. Effect of heat treatment temperatureFigure 5.11 shows the FTIR gas analysis from the samples heated to different heattreatment temperatures. Table 5.5 shows the results from proximate analysis of heat treatedleached CB samples. In the FTIR spectrum, the peak from 2268-2395 cm-1 in Figure 5.11arepresented CO2 removal from the samples due to C=O stretching vibrations [44, 172]. Thesame functional group positions were identified in all samples indicating the same type ofgases involving from the samples during heat treatment. The intensity of transmittance wasdirectly proportional to the concentration of functional groups according to Lambert-Beerlaw [186]. Increased gas evolution was seen for samples heated above 950 °C, implyingincreased removal of reaction products. With increased evolution of CO2 with increasedtemperature, more C atoms were lost (increased mass loss seen in Figure 5.12) from thesamples. This loss of C along with volatile matter resulted in a decrease of volatile contentin the samples as temperature increased (Table 5.5). The peak from 3136-2997 cm-1 (Figure5.11b) was present in the sample after 1 h of heating at 900 °C (Figure 5.11c) indicating theC-H stretching vibrations or aromatics evolving from the sample even after treatment at 900°C [86]. This indicated that 900 °C was not enough for complete devolatilization of theleached CB sample, but temperatures >950 °C were sufficient (since this peak was absent).This was also seen in the TGA proximate analysis results (Table 5.5) with 0.38% volatiles stillremaining in the sample.975.2. DEVOLATILIZATION OF LEACHED CBabFigure 5.11: Effect of heat treatment temperature on devolatilization of leached CB:FTIR gas analysis results a) At target temperature, and b) After 1h of heating at targettemperature.Figure 5.12 shows the TGA analysis results from heat treatment of leached CB atdifferent temperatures. As seen in Figure 5.12, three distinct DTA peaks were present for alltemperatures tested. The three peak temperatures are included in Appendix B (Table B.2)and the maxima of the three peaks were very close to each other. The chemistry of the threedistinct peaks is explained in detail in Section 5.2.4. The 3rd DTA peak in Figure 5.12 forsample heated at 900 °C indicated incomplete exothermic process likely because of volatilesremaining in the sample.985.2. DEVOLATILIZATION OF LEACHED CBFigure 5.12: Effect of heat treatment temperature on devolatilization of leached CB fromTGA analysis.Table 5.5: TGA proximate analysis: Effect of heat treatment temperature on devolatilizationof leached carbon black.Heat treatmenttemperature (°C) Ash (%) Volatiles (%) Moisture (%) FC (%)900 1.72 0.38 0.07 97.82950 1.70 0.19 <0.1 98.211000 1.60 0.16 <0.1 98.245.2.2. Effect of heat treatment timeFigure 5.13 shows the effect of heat treatment time on devolatilization of leached CBsample. Figure 5.13 shows the FTIR gas analysis at the end of the heat treatment process. Itwas seen that the intensity of the CO2 peak (from 2268-2395 cm-1) for sample heated for 1 hwas higher than in the case of the other samples heated for different durations. Thisindicated continued removal of C atoms from the leached CB matrix after 1 h of heating.The volatile content increased for samples heated for longer durations (>1 h) along with anincrease in ash content as seen in Table 5.6. This was due to the removal of C atoms fromthe matrix apart from the removal of volatiles. A holding time of >1 h resulted in increased995.2. DEVOLATILIZATION OF LEACHED CBremoval of C atoms instead of volatiles as seen in the FTIR gas analysis and proximateanalysis results.Figure 5.13: Effect of heat treatment time on devolatilization of leached CB: FTIR-gasanalysis of leached CB heated for different holding times.Figure 5.14 shows the TG-DTA analysis results from the three samples. Each sample hadthree distinct peaks like those seen for samples heated at different temperatures. Thisindicated that no additional reactions were proceeding when samples were heated forlonger holding times. The peak positions of the different samples were very close and areincluded in Appendix B (Table B.2). The mass loss curve for all three samples was nearlyidentical, further suggesting no improvement in devolatilization with increased holdingtime for samples. It was therefore concluded that a holding time of 1 h was sufficient fordevolatilization experiments.1005.2. DEVOLATILIZATION OF LEACHED CBFigure 5.14: Effect of heat treatment time on devolatilization of leached CB from TGAanalysis.Table 5.6: TGA proximate analysis: Effect of heat treatment time on devolatilization ofleached carbon black.Heat treatmenttime (h) Ash (%) Volatiles (%) Moisture (%) FC (%)1 1.60 0.16 <0.1 98.242 1.50 0.32 <0.1 98.093 2.96 0.38 <0.1 96.605.2.3. Effect of heating rateFigure 5.15 shows the effect of heating rate on the devolatilization of leached CB samples.The concentration of CO2 increased with an increase in the heating rate (as seen in Figure5.15). This was due to the reduced time for gas evolution at faster heating rates (as a resultof less time for heat to reach the sample core) which was also reported in the literature [186].The DTA curves (Figure 5.16) revealed a delay in all three peaks with reduction in heatingrate. The peak temperatures of the three distinct peaks for all samples are included in Table5.7. The delay in reactions for sample heated at a lower heating rate was likely because of adelay in homogeneously reaching the reaction temperatures. It was suggested that this delay1015.2. DEVOLATILIZATION OF LEACHED CBin reactions resulted in the decomposition of benzene and its rings because of secondarycracking reactions during pyrolysis of waste tires [186]. The mass loss was slightly lower forsample heated at 25 °C/min indicating that the rate was faster than required for maximumvolatile removal.Figure 5.15: Effect of heating rate on devolatilization of leached CB: FTIR-gas analysis ofleached CB heated for different heating rates.Figure 5.16: Effect of heating rate on devolatilization of leached CB from TGA analysis.1025.2. DEVOLATILIZATION OF LEACHED CBTable 5.7: Peak temperatures of DTA peaks during heating of rCB.Sample HR (°C/min) Peak 1 (°C) Peak 2 (°C) Peak 3 (°C)5 120.4 571.6 839.210 216.6 580 866.625 301.9 606.7 942.2The proximate analysis results are also included in the Table 5.8. A heating rate of 5 °C/minwas lower than the required HR (for maximum devolatilization) because of possible removalof C atoms from the matrix (cracking reactions) leading to high volatile concentration seenin Table 5.8. Therefore, a heating rate of 10 °C/min was selected as the optimum heating ratefor devolatilization of leached CB.Table 5.8: TGA proximate analysis: Effect of heating rate on devolatilization of leachedcarbon black.Sample HeatingRate (°C/min) Ash (%) Volatiles (%) Moisture (%) FC (%)25 1.66 0.26 <0.1 97.9210 1.7 0.19 <0.1 98.215 1.42 0.31 <0.1 98.125.2.4. Analysis of leached CB + heat sampleA temperature of 950 °C, at a heating rate of 10 °C/min with a holding time of 1 h wasfound to be sufficient for devolatilization of leached CB. Therefore this sample was selectedfor further analysis. This sample was termed as "leached CB+heat" in this document. Figure5.17 shows the SEM and TEM images of leached CB+heat sample. As seen in Figure 5.17b,the sample had a rough texture and cavities because of the evolution of volatiles [180]. Theagglomerate size varied considerably and was similar to leached CB sample, because ofabsence of any pulverization techniques employed. Figure 5.17c and d show the branchednature of primary particles with turbostratic arrangement of graphene layers due to hightemperature heat treatment performed on the sample.1035.2. DEVOLATILIZATION OF LEACHED CBa bc dFigure 5.17: SEM images of leached CB + heat sample: a) At 200x, b) At 1kx, and TEMimages a) At low magnification, and b) At high magnification.Table 5.9 shows the results from TGA proximate analysis experiments on leached CB +heat sample. As seen in Table 5.9, the leached CB + heat sample hadminimum ash and volatilecontents and the highest FC content of 98.21%. This further indicated effective devolatilizationof this sample.1045.2. DEVOLATILIZATION OF LEACHED CBTable 5.9: TGA proximate analysis results of leached CB + heat sample.Sample Ash (%) Volatiles (%) Moisture (%) FC (%)Raw carbon char 12.09 5.69 0.98 81.24Leached CB 1.51 6.68 1.08 90.73Leached CB + heat 1.70 0.19 <0.1 98.21Super-P 0.05 0.15 <0.1 99.7Figure 5.18 shows the TG-FTIR analysis results for preparation of leached CB + heatsample. Figure 5.18a shows the effect of temperature on the evolution of volatiles from theleached CB sample via FTIR-gas analysis. The maximum evolution of gases (with thehighest intensity) was seen after 90 min of heating and at 907 °C from the plot in Figure5.18a. No functional groups were detected up to a temperature of 400 °C from the exhaustgases, as seen in Figure 5.18b. This was because of the previous pyrolysis process resultingin decomposition of tire rubber and removal of gaseous compounds. Above 400 °C, a CO2peak was present likely due to decomposition of macromelecular substances such asbenzene and its derivatives along with unpyrolyzed remnants of rubber in the leached CBsample [7]. From 500 °C to 700 °C, an additional peak at ∼2100 cm-1 was observed,indicating the evolution of CO [186]. From 700-950 °C, additional peaks at ∼3700 cm-1 wereseen. This indicated opening of benzene and benzene derivatives forming polycyclicaromatic hydrocarbons (PAH) and their subsequent removal [186].1055.2. DEVOLATILIZATION OF LEACHED CBab cdFigure 5.18: Heat treatment of leached CB: FTIR-gas analysis from volatile evolution: a) Attemperature increments of 100 °C, b) TG-DTA analysis, and FTIR-gas analysis at c) 600 °C,and d) 900 °C). 1065.2. DEVOLATILIZATION OF LEACHED CBAs seen in Figure 5.18c, the DTA curve had three peaks, thus indicating three distinctphases evolving during the devolatilization process. The first peak was seen in less than 20mins of heating the sample (temperature <120 °C) andwas associatedwithmoisture loss [172].The next two peaks observed in the sample can be categorized as decomposition (400-700 °C)and secondary reactions (700-950 °C). The decomposition referred to the decomposition ofresidual rubber remaining in the leached CB sample as a result of an incomplete pyrolysisprocess. During this primary decomposition, light aliphatic gases (C2-C5) formed along withCO2 (Figure 5.18d)[172]. During the third phase of devolitilization, volatiles were expectedto escape. This led to the decomposition of benzene, benzene derivative and S containingcompounds [186]. This wasmarked by O-H stretching vibrations seen for temperatures above700 °C (Figure 5.18e). The remaining mass at the end of the third phase was composed ofrCB along with non-decomposible fillers [186]. This was found to be traces of Si containingcompounds from SEM-EDS analysis which could not be removed from the leached CBmatrix.The BET adsorption isotherm and pore size distribution of raw carbon char, leached CBand leached CB + heat samples are included in Figure 5.19. According to the IUPACclassification, the adsorption isotherm for all three samples was an intermediate betweenType I and II mainly consisting of macropores [181]. This was further verified by the poresize distribution curve included in Figure 5.19b. Micropores and mesopores were almostabsent in all the samples due to lack of use of an activating agent. The information on porevolumes from the three samples in included in Appendix B of the thesis (Table B.3). The SBETof leached CB + heat sample was slightly higher (76 m2/g) when compared to leached CB (68m2/g).1075.2. DEVOLATILIZATION OF LEACHED CBabFigure 5.19: BET analysis of leached CB + heat sample: a) Adsorption isotherm, and b) Poresize distribution.Figure 5.20 shows the results from FTIR analysis of the leached CB + heat sample. Asseen in the Figure 5.20, no functional groups were attached to the C matrix. This indicateda possible removal of volatiles attached to the C-matrix after the heat treatment. The traceamount of volatiles and ash detected in the proximate analysis experiments (Table 5.9) werenot detected during the FTIR analysis, due to their low concentrations.1085.2. DEVOLATILIZATION OF LEACHED CBFigure 5.20: FTIR analysis of leached CB + heat sample.Figure 5.21 and Table 5.10 shows the results from Raman spectroscopy analysis ofleached CB+ heat sample. The ID/IG ratio reduced for the leached CB + heat sample (whencompared to leached CB sample) due to graphitization of the material during heat treatmentexperiments, as reported in literature [99, 187]. The La value also increased as a result of thischange due to the evolution of volatiles from the leached CB matrix, as seen from proximateanalysis experiments with only 0.19% volatiles remaining in the leached CB + heat sample(Table 5.9). The G band position also shifted to a higher wave number (1602 cm-1) furtherimplying increased graphitization of CB nanoparticles [35]. Considering the low volatileand ash content and graphitization of the leached CB + heat sample, this sample was furtherselected for electrochemical testing in Li-ion systems.1095.3. SUMMARYFigure 5.21: Raman spectroscopy and curve fitting of leached CB + heat sample.Table 5.10: Raman spectroscopy results for leached CB + heat sample.Sample Leached CB Leached CB + heat Super-PR2 0.902 0.885 0.966D band position(cm-1) 1337.68 1339.52 1338.96Intensity (a.u.) 0.32 0.52 0.76G band position(cm-1) 1580.29 1602.78 1590.06Intensity (a.u.) 0.29 0.73 0.88ID/IG 1.08 0.72 0.86La (nm) 4.06 6.01 5.745.3. SummaryThis chapter discussed the effect of heat treatment on the structure and chemistry ofleached CB sample. Activation of leached CB was performed using CO2 and KOH. CO2activation resulted in lower SBET (803 m2/g) and pore volume of samples when compared toKOH (maximum SBET=994 m2/g). FTIR analysis revealed the presence of C=C bond attachedto the CO2AC matrix, whereas O-H and C-H functional groups were also detected in thematrix of the KOHAC samples. These functional groups were likely indicative of the1105.3. SUMMARYvolatiles remaining in the AC samples as seen by proximate analysis experiments. Ramananalysis revealed partial graphitization in the AC samples (ID/IG=0.84 and 0.92 for CO2 andKOHAC). This was verified by an improvement in the electrical conductivity of the ACsamples. CO2AC (1000-3) and KOHAC (900-2-4) were therefore selected for electrochemicalexperiments because of their high SBET, pore volume and electrical conductivity.Devolatilization experiments revealed that a temperature of at least 950 °C was requiredfor the removal of volatiles from the leached CB sample. An increase in heating time >1 hresulted in increased removal of C atoms increasing ash and volatile content in the samples. Afast heating rate of 25 °C/min resulted in volatiles remaining in the sample due to insufficienttime for heat to reach the core of the particles. FTIR-gas analysis experiments revealed theevolution of mainly CO2, CO and light aliphatic gases during heat treatment of leached CB.A temperature of 950 °C, with a holding of 1 h at a heating rate of 10 °C/min was optimumfor almost complete removal of volatiles from the leached CB sample (Table 5.9). This samplewas referred to as "leached CB + heat" and the removal of volatiles was further verified by theabsence of any functional groups detected in the FTIR analysis. The SBET value of leached CB+ heat was only 8 m2/g higher than leached CB due to lack of activating agents. The leachedCB + heat sample had the highest FC content (98.21%) out of all the rCB grades producedin this work. Therefore, this sample was selected for electrochemical experiments in Li-ionsystems.111Chapter 6: Results and Discussion:Electrochemical TestingThis chapter presents the results obtained from the electrochemical experiments using thedifferent grades of recovered carbon black in Li-ion half cells. The effect of the followingtreatments on the electrochemical performance of the Li-ion cells was evaluated: Effect ofchemical treatment (Section 6.1), Effect of heat treatment (Section 6.2) and, Effect of activationof leached CB (Section 6.3).6.1. Effect of chemical treatment of raw carbon char onspecific discharge capacityThe results from electrochemical experiments of half cells fabricated with the raw carbonchar and leached CB are included in the following text. Although rCB yielded stable dischargecapacity values when introduced to anodes in Li-ion half cells, the coulumbic efficiency of allthe cells tested was relatively low (for the first few cycles of discharge). Thus, use of the rCBwas also explored as an additive in commercially used LTO systems.6.1.1. Chemically treated rCB as anodeFigure 6.1 shows the results from electrochemical testing of Li-ion half cells withchemically treated rCB (leached CB) used as electrode at 0.5 C (charge rate). Figure 6.1ashows the cycling stability of the raw carbon char, leached CB and Super-P cells. The rawcarbon char electrode yielded the minimum stable specific discharge capacity (capacity afterfirst few cycles of discharge, out of all rCB samples tested in this work) likely because of its1126.1. EFFECT OF CHEMICAL TREATMENT OF RAW CARBON CHAR ON SPECIFIC DISCHARGE CAPACITYdisorder (Table 5.4) and high impurity content (Table 3.1). The stable discharge capacityimproved for leached CB sample (by 74%) when compared to raw carbon char as seen in theFigure 6.1a as a result of impurity removal. However, due to a number of functional groupsstill attached to the rCB matrix (FTIR analysis from Figure 4.13b) and amorphous nature ofthe leached CB sample (Figure 4.11) the improvement in terms of stable specific dischargecapacity was limited. The stable discharge capacity of Super-P CB was higher than allchemically treated samples due to its high purity (Table 5.9) and graphitization (Figure B.1)as a result of high temperature manufacturing process for its production [17]. Apart fromreducing the stable specific discharge capacity, the impurities in rCB samples also resultedin the irreversible formation of SEI layer after the first cycle of discharge due to Lientrapment [188]. The irreversible capacity drop (decrease in capacity after 1st discharge) ofthe cells is included in Table 6.1. As seen in Table 6.1, the maximum capacity reduction wasobserved for the raw carbon char electrode, due to likely undesirable and irreversible sidereactions as a result of impurities present on its structure. The minimum loss was observedfor Super-P electrode due to its higher purity.Figure 6.1b shows the charge discharge curves for the 1st cycle for all chemically treatedrCB cells. The discharge curves were the curves originating from ∼3 V at 0 on the x-axiswhereas, the charge curves were the ones stating at ∼0 V at 0 x-intercept. As seen in thedischarge profiles, the leached CB and the raw carbon char had sloping profiles, which istypical of turbostratic intercalation in hard carbon anodes [189]. Whereas a plateau at ∼1 Vwas seen for Super-P cell. This plateau was linked to the SEI formation in the cells and wasmore evident in Super-P likely because of its higher surface area (90 m2/g) [188, 189] than thatof the rCB samples (by >20 m2/g). As a result of this higher SBET, the electrolyte reduction(of likely EC) was more evident and therefore took place at∼1 V in the Super-P electrodes asalso reported in the literature [188]. With continued cycling this plateau was not present dueto irreversible Li-intercalation and SEI formation in the Super-P anode cells.1136.1. EFFECT OF CHEMICAL TREATMENT OF RAW CARBON CHAR ON SPECIFIC DISCHARGE CAPACITYabFigure 6.1: Cycling of chemically treated rCB electrodes as anode at 0.5C: a) Specificdischarge capacity with respect to cycle number, and b) Charge discharge curves.Table 6.1: Specific discharge capacity of chemically treated rCB anode cells after differentcycles of charge and discharge.Sample Fixed carbon(%)Cycle 1(mAh/g)Cycle 2(mAh/g)Cycle 25(mAh/g)Cycle 50(mAh/g)Raw CB 81 600 94 89 85Leached CB 90 558 165 143 148Super-P 99 888 572 545 5801146.1. EFFECT OF CHEMICAL TREATMENT OF RAW CARBON CHAR ON SPECIFIC DISCHARGE CAPACITYIn order to further understand the suitability of these electrodes at different chargingconditions, rate test was performed on chemically treated rCB cells. The results from ratetests are included in Figure 6.2. The stabilized discharge capacities after 10 cycles for thedifferent C-rates are also included in Table 6.2. The capacity obtained from all electrodesreduced with an increase in the C-rate, indicating kinetic limitation for Li-diffusion [188, 190].This implied insufficient time for Li intercalation in carbon and its deposition on the electrodesurface. When the rate was reduced back to 0.1 C, the initial capacity was recovered for allcells indicating good reversibility of the materials [190]. The minimum reduction in capacitywith increase in C rate was for Super-P carbon black, due to its high purity and SBET allowingeasy Li ion intercalation even at higher rates [188].Table 6.2: Specific discharge capacity of chemically treated rCB anode cells after 10 cyclesfor different C rates.Sample 0.1 C(mAh/g)0.2 C(mAh/g)0.5 C(mAh/g)1 C(mAh/g)2 C(mAh/g)0.1 C(mAh/g)Raw carbon char 288 247 171 116 63 304Leached CB 332 297 240 198 156 457Super-P 637 607 574 536 495 6891156.1. EFFECT OF CHEMICAL TREATMENT OF RAW CARBON CHAR ON SPECIFIC DISCHARGE CAPACITYFigure 6.2: Effect of C rate on specific discharge capacity from chemically treated rCB usedas anode.EIS analysis was also performed before electrochemical tests to understand the chemistry(resistances) of these cells. The resulting Nyquist plot is included in Figure 6.3. A modifiedRandle’s circuit (Figure 3.7) was used for curve fitting to determine the various parametersfrom EIS analysis [171, 191]. The data obtained from standard curve fitting techniques isincluded in Table 6.3.Table 6.3: Electrochemical parameters obtained from curve fitting of EIS results.Sample RS (Ω) Cs (F) Rct (Ω) W (Ω) chi sqRaw carbon char 20.05 6.52 x 10-7 242.70 1.06 x 10-3 0.08±8.4% ±12.2% ±9.6% ±9.4%Leached CB 4.90 2.06 x 10-6 139.40 1.59 x 10-3 0.12±10.3% ±12.0% ±12.2% ±10.8%1166.1. EFFECT OF CHEMICAL TREATMENT OF RAW CARBON CHAR ON SPECIFIC DISCHARGE CAPACITYFigure 6.3: EIS test results from chemically treated rCB used as anodes before cyclingexperiments(Nyquist plot).The intercept of the semi-circle in the high frequency region depicts the ohmic resistanceof the cell mainly due to electrolyte and electrode resistance (Rs) [192, 193]. The high value ofRs for raw carbon char was likely due to its low electrical conductivity (Figure 4.11). This ledto high resistance values in the cell, as seen in the EIS analysis results (Table 6.3). The chargetransfer resistance (Rct) was related to the radius of the high frequency semi-circle, whichrelated to the resistance of Li-ion transfer from electrolyte to rCB surface at the interfaceof the electrode and electrolyte[134, 193]. This value was lower for leached CB cell, due tosuccessful removal of impurity elements responsible for hindering Li-ion intercalation (Table5.9). The capacitance in the cells (Cs) was related to the double layer and passive film relatedcapacitance [149, 194, 195]. This layer was formed due to accumulation of charged speciesaround the interface of the electrode and the electrolyte. Also, the inclined line in the Nyquistplot represented resistance to diffusion of Li within the pores in the rCB represented by theWarburg impedance (W) [193, 196]. Therefore, it was concluded that removal of metallicimpurities by chemical treatment led to improvement in the electrochemical performance ofthe cells. However, the improvement was limited due to the carbon’s amorphous structure1176.1. EFFECT OF CHEMICAL TREATMENT OF RAW CARBON CHAR ON SPECIFIC DISCHARGE CAPACITYand high impurity content.6.1.2. Chemically treated rCB in LTO anodesFigure 6.4 includes cycling information of chemically treated rCB sample whenincorporated as additive to LTO anodes. As seen in Figure 6.4a, the stable discharge capacitywas drastically reduced (by 95%) for raw carbon char doped LTO cell when compared toleached CB. This was attributed to the presence of impurities in the raw carbon char (Table5.9) resulting in unwanted side reactions resulting in irreversible Li-ion deposition [188].The irreversible capacity loss was evident for both leached CB and raw carbon char dopedLTO cells for the first few cycles of charging. This was expected due to the volatiles stillremaining in the samples after chemical treatments (Table 5.9). These volatiles (e.g., S)irreversibly combined with Li-ions to form insoluble compounds with continued cycling forthe first few cycles (peak of the charge curve for leached CB sample in Figure 6.4b). In orderto understand the reactions taking place during cycling, the charge and discharge curveswere plotted (Figure 6.4b).Figure 6.4b includes the charge discharge curve from the first cycle for chemicallytreated rCB used as additive in LTO anode. It was found that the charge curve of raw carbonchar and leached CB had a peak (∼2.2-2.8 V). The peak was attributed to the presence of Scontaining compounds in the rCB matrix leading to the formation of LixSy, as was alsoreported in literature [197]. However, on continued cycling of these electrodes, this peakwas not present likely due to irreversible deposition of reaction products on the anode (forinstance Li2S) (Figure C.8) [198]. This was directly related to the loss in discharge capacityfor the first few cycles of the cells. Therefore, the extra capacity from these cells was byvirtue of the volatiles and impurities present in the rCB and not due to LTO. This peak wasnot seen in the C anodes likely because of stable SEI formation (on reaction with S) atpotentials below 1 V. Since LTO anodes were tested at higher potential (>1 V), the SEI layerdid not form, resulting in interference from S in the battery performance. The specific1186.1. EFFECT OF CHEMICAL TREATMENT OF RAW CARBON CHAR ON SPECIFIC DISCHARGE CAPACITYdischarge capacities after different cycles for the samples are also included in Table 6.4.Super-P had the minimum drop in specific capacity due to its high purity, high electricalconductivity and absence of volatiles.abFigure 6.4: Cycling of LTO + chemically treated rCB electrodes as anode at 0.5C: a) Specificdischarge capacity with respect to cycle number, and b) Charge discharge curves.1196.1. EFFECT OF CHEMICAL TREATMENT OF RAW CARBON CHAR ON SPECIFIC DISCHARGE CAPACITYTable 6.4: Specific discharge capacity of chemically treated rCB doped LTO anodes afterdifferent cycles of charge and discharge.Sample Fixed carbon(%)Cycle 1(mAh/g)Cycle 2(mAh/g)Cycle 25(mAh/g)Cycle 50(mAh/g)Raw CB 81 54 36 6 5Leached CB 90 135 127 94 90Super-P 99 123 123 117 116In order to understand fast charging characteristics of the cell, rate tests were performedand the results are included in Figure 6.5. The stable discharge capacity at each C-rate is alsoincluded in Table 6.5. As seen in Figure 6.5, the initial capacity was retained in all cells afterthe completion of the rate test (at 0.1 C) indicating good reversibility of electrodes. It wasfound that Super-P doped LTO electrode had a superior rate performance when compared torCB cells. The leached CB and raw carbon char had poor rate performance with almost nodischarge capacity obtained at 1 C and 2 C values. This was likely due to limitations relatedto diffusion of Li-ions due to insufficient time for charging the electrodes. Almost no capacitywas obtained from raw carbon char doped LTO cell at 0.5 C, 1 C, and 2 C due to Li depositionon the rCB electrode surface due to insufficient time for Li-intercalation in the electrodes asalso seen by the presence of deposits on electrode surface from SEM imaging after cycling(Figure C.4). Leached CB doped LTO cells demonstrated a capacity of 36 mAh/g even at 2 Crate, implying movement of Li-ions in the electrodes even at high rates.Table 6.5: Specific discharge capacity of chemically treated rCB doped LTO anode cells after10 cycles for different C rates.Sample 0.1 C(mAh/g)0.2 C(mAh/g)0.5 C(mAh/g)1 C(mAh/g)2 C(mAh/g)0.1 C(mAh/g)Raw carbon char 57 37 11 1 0 54Leached CB 129 118 95 68 36 125Super-P 147 143 133 116 87 1451206.1. EFFECT OF CHEMICAL TREATMENT OF RAW CARBON CHAR ON SPECIFIC DISCHARGE CAPACITYFigure 6.5: Effect of C rate on the specific discharge capacity of chemically treated rCBdoped LTO anodes.Figure 6.6 shows the results of EIS analysis test to determine the internal resistances ofthe cells. A modified Randle’s circuit was used for standard curve fitting and the calculatedelectrochemical parameters are included in Table 6.6. The RS values for both (raw carbonchar and leached CB) cells were similar, indicating consistency in cell fabrication and similarelectrolyte and electrodes resistances. Since raw carbon char had no clear semi-circle (dueto its infinitely high resistance), the Rct value was computed as extremely low with a higherror, as seen in Table 6.6. Also, the W value was lower for leached CB cell, indicating alower resistance to Li-ion movement in leached CB cells. Therefore, it was seen that chemicaltreatments on raw carbon char improved the additive performance considerably, howeverpresence of volatiles in the samples interfered with the cell’s performance.Table 6.6: Electrochemical parameters obtained from curve fitting of EIS results.Sample RS (Ω) Cs (F) Rct (Ω) W (Ω) chi sqRaw carbon char 5.67 4.65 x 10-7 1.22 x 10-2 3.02 x 10-5 0.17±23.4% ±9.9 x 104% ±4.1 x 109% ±8.9%Leached CB 5.14 1.29 x 10-6 183.5 2.65 x 10-4 0.16±13.0% ±14.2% ±25.6% ±10.4%1216.2. EFFECT OF HEAT TREATMENT OF RCB ON SPECIFIC DISCHARGE CAPACITY OF LI-ION BATTERIESFigure 6.6: EIS test results from chemically treated rCB doped LTO anodes before cyclingexperiments (Nyquist plot).6.2. Effect of heat treatment of rCB on specific dischargecapacity of Li-ion batteriesThe leached CB + heat sample with almost no functional groups and higher purity wastested with respect to the leached CB sample to see the effect of heat treatment on theelectrochemical behavior of the Li-ion systems. The results are included in the followingsubsections.6.2.1. Heat-treated rCB as anodeFigure 6.7 includes the results of discharge capacity measurements during cycling of heat-treated rCB anode. Figure 6.7a shows that the stable discharge capacity was improved by heattreatment (devolatilization) of leached CB by a factor of 2.30. The irreversible capacity lossfor the leached CB + heat was drastically reduced due to the removal of functional groupsand volatiles from the rCB matrix, as seen in FTIR analysis (Figure 5.20). This prevented1226.2. EFFECT OF HEAT TREATMENT OF RCB ON SPECIFIC DISCHARGE CAPACITY OF LI-ION BATTERIESunwanted side reactions to occur during the formation of SEI layer. The discharge capacitiesafter different cycles are included in Table 6.7. The leached CB + heat sample was the samplewith minimum reduction of capacity out of all the samples tested in this work. This was dueto the removal of surface functional groups from the structure of the rCBmatrix thus avoidingirreversible side reactions. Also, partial graphitization of the sample (Figure 5.21) resulted inimprovement in the electrical conductivity of the electrodes, allowing reversible intercalationof Li-ions.Figure 6.7b shows the charge and discharge curves for the first cycle for heat-treated rCBsamples used as anode. The surface area of leached CB + heat sample was slightly higherthan the leached CB only, therefore a small plateau was seen (∼0.8 V) due to formation ofthe SEI [199]. This was not visible with continued cycling of the electrode due to irreversibleLi-insertion during the first discharge. In order to explore the use of heat-treated rCB in fastcharging applications, rate tests were performed on the samples.Table 6.7: Specific discharge capacity drop after 1 cycle of charge and discharge for heat-treated rCB anode.Sample Fixed carbon(%)Cycle 1(mAh/g)Cycle 2(mAh/g)Cycle 25(mAh/g)Cycle 50(mAh/g)Leached CB 90 558 165 143 148Leached CB + heat 98 555 370 331 341Super-P 99 888 572 545 5801236.2. EFFECT OF HEAT TREATMENT OF RCB ON SPECIFIC DISCHARGE CAPACITY OF LI-ION BATTERIESabFigure 6.7: Cycling of heat-treated rCB anode at 0.5C: a) Specific discharge capacity withrespect to cycle number, and b) Charge discharge curves.Figure 6.8 includes the results obtained from rate tests on heat-treated rCB in Li-ion cellsas anodes. The discharge capacity of cells at the different C-rates after 10 cycles is includedin Table 6.8. No significant improvement in rate performance was seen as a result of the heattreatment due to limited increase in the SBET values. It was also observed that all rCB sampleshad an improvement in capacity at 0.1 C after the rate test was finished. The most likely1246.2. EFFECT OF HEAT TREATMENT OF RCB ON SPECIFIC DISCHARGE CAPACITY OF LI-ION BATTERIESreason for this was electrolyte depletion, and Li deposition with continued cycling, as wasreported in literature [200]. In order to further understand the reason for this increase, thiselectrode was analysed using SEM analysis after different cycles of charging and discharging.The results from SEM imaging are included in Figure 6.9.Figure 6.8: Effect of C rate on the specific discharge capacity of heat-treated rCB anode.Table 6.8: Specific discharge capacity of heat-treated rCB anode cells after 10 cycles fordifferent C rates.Sample 0.1 C(mAh/g)0.2 C(mAh/g)0.5 C(mAh/g)1 C(mAh/g)2 C(mAh/g)0.1 C(mAh/g)Leached CB 332 297 240 198 156 457Leached CB + heat 421 371 325 292 259 402Super-P 637 607 574 536 495 6891256.2. EFFECT OF HEAT TREATMENT OF RCB ON SPECIFIC DISCHARGE CAPACITY OF LI-ION BATTERIESa bc de fFigure 6.9: SEM images of leached CB + heat anode: a) Virgin, and after charge-dischargeof: b) 1 cycle, c) 25 cycles, d) 50 cycles, and e) 100 cycles.1266.2. EFFECT OF HEAT TREATMENT OF RCB ON SPECIFIC DISCHARGE CAPACITY OF LI-ION BATTERIESAs seen in the Figure 6.9a, the surface of the virgin electrode appeared porous and wellbound to the Cu-substrate underneath it. After 1 cycle of discharge and charge, the electrodestill appeared porous with no noticeable change (Figure 6.9b). With continued cycling after 25cycles, the porosity appeared to reduce on the surface of the electrode likely due to absorptionof Li in the surface pores (Figure 6.9c), which was also reported in literature [201]. After 50cycles of charging, a surface layer was observed to grow on the carbon surface with almostno visible porosity remaining in the sample (Figure 6.9d). This layer was believed to be Lidendrites like those often reported in literature [202]. As seen in Figure 6.9e and f, this surfacelayer grew and was similar to Li-dendrites found in graphite electrodes during fast charging[203]. This indicated that at the tested C-rate, Li-ions could not diffuse completely in thesubstrate during charging and therefore were just deposited on the surface.Figure 6.10 includes the discharge curve of the leached CB + heat sample for the first threecycles. For the first discharge cycle, SEI was expected to form with a small volatage plateau(∼0.8 V) due to its slightly higher SBET and porous structure. With further cycling, a slopingdischarge curve was seen for the rCB sample, which is typical for turbostratic carbon [204].Figure 6.10: Discharge curves for the first three cycles of leached CB + heat anode.1276.2. EFFECT OF HEAT TREATMENT OF RCB ON SPECIFIC DISCHARGE CAPACITY OF LI-ION BATTERIESEIS analysis was also performed to understand the internal resistance of the cells. Theobtained Nyquist plot is included in Figure 6.11 and electrochemical parameters are providedin Table 6.9. The RS values were similar (for leached CB and leached CB+heat half cells)indicating similar electrolyte and electrode resistance of the cell. Rct was lower for the leachedCB + heat cell, due to the graphitization of leached CB + heat sample (Figure 5.21) indicatingimproved performance of the anode. Therefore, it was observed that the discharge capacityof the cells was improved by performing heat treatment on the leached CB sample. Thiswas possible because of purification and removal of volatile compounds from the leached CBsample. However, no improvement in rate capacity was achieved due to limited improvementin the SBET of the leached CB + heat sample.Figure 6.11: EIS test results from heat-treated rCB anode before cycling experiments(Nyquist plot).1286.2. EFFECT OF HEAT TREATMENT OF RCB ON SPECIFIC DISCHARGE CAPACITY OF LI-ION BATTERIESTable 6.9: Electrochemical parameters for leached CB + heat anode obtained from curvefitting of EIS results.Sample RS (Ω) Cs (Ω) Rct (Ω) W (Ω) chi sqLeached CB 4.90 2.06 x 10-6 139.40 1.59 x 10-3 0.12±10.3% ±12.0% ±12.2% ±10.8%Leached CB + heat 3.76 1.79 x 10-6 115.9 1.26 x 10-3 0.16±12.6% ±13.9% ±15.3% ±11.6%6.2.2. Heat-treated rCB in LTO anodesFigure 6.12 shows the cycling behavior of heat-treated rCB doped LTO electrodes. Thevalues of discharge capacity after different cycles are included in Table 6.10. It was observed(Figure 6.12a) that the discharge capacity of 1st cycle was lower for the leached CB + heatdoped LTO anode when compared to the leached CB doped LTO anode. This was due toeffective removal of volatiles and functional groups attached to the leached CB matrix. Thespecific capacity of the leached CB sample reduced for the first few cycles consistently as seenin Figure 6.12a, due to side reactions from the presence of functional groups and volatilesattached to the leached CB matrix [197].Figure 6.12b shows the charge-discharge curves for the first cycle of leached CB + heatdoped LTO electrode. The small peak at ∼2.3 V was eliminated in this electrode whencompared to the electrode made with leached CB, because of effective removal of volatiles(S) from the leached CB + heat matrix upon its heat treatment. However, the overpotential(distance between charge and discharge curves at V=1.5 V) was higher for leached CB + heatsample (than leached CB only sample) due to the removal of S containing volatiles, as seenfrom proximate analysis results revealing only 0.19% volatiles in leached CB + heat sample.This was expected, since heteroatoms like S were known to impart increased capacity in Canodes [197]. Therefore, the resultant stabilized discharge capacity from this sample waslower than that of the leached CB + LTO electrode. This was also observed in the EISanalysis results indicating higher charge transfer resistance for leached CB + heat sample(Figure 6.13).1296.2. EFFECT OF HEAT TREATMENT OF RCB ON SPECIFIC DISCHARGE CAPACITY OF LI-ION BATTERIESTable 6.10: Specific discharge capacity drop of heat-treated rCB doped LTO anodes afterdifferent cycles of charge and discharge.Sample Fixed carbon(%)Cycle 1(mAh/g)Cycle 2(mAh/g)Cycle 25(mAh/g)Cycle 50(mAh/g)Leached CB 90 135 127 94 90Leached CB + heat 98 102 94 84 83Super-P 99 123 123 117 116abFigure 6.12: Cycling of heat-treated rCB doped LTO anodes at 0.5C: a) Specific dischargecapacity with respect to cycle number, and b) Charge discharge curves.1306.2. EFFECT OF HEAT TREATMENT OF RCB ON SPECIFIC DISCHARGE CAPACITY OF LI-ION BATTERIESSince no improvement was expected in the rate test performance of these electrodes (dueto limited increase in the SBET) the rate test was not performed for this set of cells. Theinternal resistance of the cells was measured using EIS analysis and the results are included inFigure 6.13 and Table 6.11. The Rs values for both cells were similar indicating stability of theelectrolyte used and similar electrode resistances. The Rct of leached CB + heat doped LTO cellwas higher than that of the leached CB sample, indicating reduced electrical conductivity ofthe rCB+LTO composite. This was the reason for reduced discharge capacity from the leachedCB + heat doped LTO anodes. The Cs value for leached CB + heat sample was lower due toeffective removal of functional groups from the surface resulting in reduced interactions at theelectrode-electrolyte interface. In order to understand the reason for this increased resistance,SEM imaging was performed on the cycled leached CB + heat doped LTO electrodes (after100 cycles) and the results are included in Figure 6.14.Figure 6.13: EIS test results from heat-treated rCB doped LTO anodes before cyclingexperiments (Nyquist plot).1316.2. EFFECT OF HEAT TREATMENT OF RCB ON SPECIFIC DISCHARGE CAPACITY OF LI-ION BATTERIESTable 6.11: Electrochemical parameters of heat-treated rCB doped LTO anode obtained fromcurve fitting of EIS results.Sample RS (Ω) Cs (F) Rct (Ω) W (Ω) chi sqLeached CB 5.14 1.29 x 10-6 183.5 2.65 x 10-4 0.16±13.0% ±14.2% ±25.6% ±10.4%Leached CB + heat 5.76 9.46 x 10-7 601.1 3.53 x 10-4 0.06±11.6% ±10.4% ±14.2% ±11.2%As seen in the Figure 6.14a, no visible cracks were evident even after cyclingexperiments were completed. This indicated stability of the surface SEI layer formed as alsoseen in the cycling experiments (Figure 6.12a). The smaller particles seen in Figure 6.14bwere LTO particles, while the bigger ones were rCB. On close examination at highermagnifications, it was observed that bigger agglomerates of rCB were covered by the LTOpowder. Since LTO by itself had a very low electrical conductivity value, the contactbetween the leached CB + heat was lower leading to higher resistance values. This was alsopossible for the leached CB + LTO composite electrode because of absence of anypulverisation techniques during electrode fabrication. Also, presence of volatiles in leachedCB sample resulted in additional Li insertion sites for added capacity in the leached CB cells.This was undesired since rCB was added for the sole purpose of improving electricalconducvity and not Li-insertion in the rCB. It was therefore concluded that removal ofvolatiles from the rCB surface effectively improved the coulumbic efficiency of the rCBdoped LTO cells during the first few cycles, however for improvement in rate performanceof the cells, SBET improvement was required.1326.3. EFFECT OF ACTIVATION EXPERIMENTS OF RCB ON SPECIFIC DISCHARGE CAPACITY OF LI-ION BATTERIESa bFigure 6.14: Structure of heat-treated rCB doped LTO anode after 100 cycles of charging anddischarging obtained from SEM analysis: a) At 500x, and b) At 5Kx.6.3. Effect of activation experiments of rCB on specificdischarge capacity of Li-ion batteriesThe primary objective of activation experiments was to increase the SBET and pore volumeof leached CB sample. Subsequently, the primary purpose of fabricating cells with activatedleached CB was to study the effect of SBET on the electrochemical performance of Li-ion cells.6.3.1. Activated rCB as anodeFigure 6.15 shows the effect of cycling on the specific discharge capacity of Li-ion batterieswith activated rCB electrodes. It was found that the specific discharge capacity of KOHAC(900-2-4) was the highest out of all the rCB grades tested in this work (Figure 6.15a). This wasdue to its partial graphitization (Table 5.4) and higher electrical conductivity (Figure 5.9a)and higher SBET (965 m2/g) when compared to other grades of rCB. A high SBET resulted inbetter contact between electrode and electrolyte, providing a number of active sites for charge1336.3. EFFECT OF ACTIVATION EXPERIMENTS OF RCB ON SPECIFIC DISCHARGE CAPACITY OF LI-ION BATTERIEStransfer reactions to proceed and also a shorter diffusion length for easy movement of Li-ions[171, 190, 205].The high SBET along with surface functional groups attached to the rCB matrix resultedin improved wetting and therefore higher capacity values for the first cycle [206]. However,after the first discharge cycle, the Li-ions reacted irreversibly with these functional groupsresulting in a high irreversible capacity drop thus reducing the coulumbic efficiency of thecells considerably (Table 6.12). This loss in capacity was also related to the SEI layer formationas a result of catalytic reduction of electrolyte components due to the high SBET values of thesamples [190, 205, 207]. Similar results were reported when pyrolyzed biomass sample wasused as anode in Li-ion systems [208]. Due to low SBET of Super-P when compared to activatedrCB samples, the irreversible capacity loss was less than in the case of the activated rCB cells.1346.3. EFFECT OF ACTIVATION EXPERIMENTS OF RCB ON SPECIFIC DISCHARGE CAPACITY OF LI-ION BATTERIESabFigure 6.15: Cycling of activated rCB anode at 0.5C: a) Specific discharge capacity withrespect to cycle number, and b) Charge discharge curves.Figure 6.15b shows the charge-discharge curves of cells with activated rCB electrodes. Alarge hysteresis (plateau in the discharge curve at >0.7 V) for the high SBET samples was seen inFigure 6.15bwith increased capacity. This is similar to results for non-graphitic C anodes [209,210]. This plateau was related to the formation of the SEI layer during the first discharge cyclein these cells. It was suggested that the C/H ratio also had a direct role to play in discharge1356.3. EFFECT OF ACTIVATION EXPERIMENTS OF RCB ON SPECIFIC DISCHARGE CAPACITY OF LI-ION BATTERIEScapacity of Li-ion cells from pyrolyzed samples. Li reacts with surface functional groups (Hatoms) irreversibly, thus contributing to the initial loss in capacity [190, 204]. Hence, a largeamount of Li was lost and became unavailable for subsequent charge-discharge cycles foractivated rCB samples. This hysteresis is undesirable, because Li-ion is removed from the C-matrix at a higher voltage than the voltage for removal of Li from graphitic layers of carbon[204]. In practical applications, this reduces the overall cell voltage. This was clearly seen inthe KOHAC (900-2-4) andCO2AC (1000-3) samples. TheHwas detected in FTIR analysis of theACs with O-H and C-H functional groups still present in the AC matrix, further highlightingthe possibly undesirable effect of these functional groups (Figure 5.4 and Figure 4.13).Table 6.12: Specific discharge capacity of activated rCB anodes after different cycles ofcharge and discharge.Sample SBET (m2/g)Cycle 1(mAh/g)Cycle 2(mAh/g)Cycle 25(mAh/g)Cycle 50(mAh/g)Leached CB 68 558 165 143 148Super-P 90 888 572 545 580CO2AC (1000-3) 803 1425 658 463 463KOHAC (900-2-4) 965 1853 610 572 548The suitability of activated rCB for fast charging application was explored byperforming rate tests from which the results are included in Figure 6.16 and Table 6.13. Itwas observed that a specific discharge capacity was retained after the rate tests werefinished for the activated rCB anodes pointing to stability in its structure [183]. The ACelectrodes showed good rate capacity even at 2 C with capacity retention of ∼40% of itsdischarge capacity at 0.1 C. However, at the beginning of the rate test, the dischargecapacity was variable as a result of irreversible side reactions between the functional groupspresent on the surface of the rCB and Li.1366.3. EFFECT OF ACTIVATION EXPERIMENTS OF RCB ON SPECIFIC DISCHARGE CAPACITY OF LI-ION BATTERIESFigure 6.16: Effect of C-rate on the specific discharge capacity of activated rCB used asanodeTable 6.13: Specific discharge capacity of activated rCB anode cells after 10 cycles fordifferent C rates.Sample 0.1 C(mAh/g)0.2 C(mAh/g)0.5 C(mAh/g)1 C(mAh/g)2 C(mAh/g)0.1 C(mAh/g)Leached CB 332 297 240 198 156 457CO2AC (1000-3) 514 416 311 262 188 467KOHAC (900-2-4) 703 547 371 313 234 610Super-P 637 607 574 536 495 689SEM analysis was performed on the KOHAC (900-2-4) electrode to understand thereason for its high capacity. Figure 6.17 shows the SEM images of the virgin KOHAC(900-2-4) electrode and also the electrode subjected to 100 cycles of charge and discharge.Figure 6.17a shows the porous structure of KOHAC (900-2-4) electrode before cyclingexperiments were conducted. As seen in Figure 6.17b, the pores appear darker in color (inBSE) due to lower atomic number of Li. Figure 6.17c and d reveal the morphology of thesedeposits on the surface at higher magnifications. These deposits of Li were not seen in thevirgin electrode (Figure 6.17a). Particle Li deposition was expected to be a result of1376.3. EFFECT OF ACTIVATION EXPERIMENTS OF RCB ON SPECIFIC DISCHARGE CAPACITY OF LI-ION BATTERIESadsorption of Li clusters in rCB pores like reported in literature [203]. As a result of thisdeposition, the discharge capacity from the sample increased with continuous charging anddischarging. The deposition of Li on the surface of the rCB matrix instead of itsintercalaction in the substrate resulted in this increase of capacity of activated rCBelectrodes. Similar surface deposits were found for the CO2AC (1000-3) electrode furtherindicating the role of SBET in their formation (Appendix C Figure C.5). Similar deposits wereseen in literature during fast charging of amorphous carbon anodes [211]. During fastcharging of electrodes, Li plating (at potential below 0 V) occurs due to deviation ofpotential of the cell from the equilibrium potential [212]. This shift in potential is due topolarization (ohmic drop, charge transfer overpotential and diffusion overpotential) in thecells. Experimentally, due to localized changes in the potential of the anode bothintercalation and deposition may occur at the same time.1386.3. EFFECT OF ACTIVATION EXPERIMENTS OF RCB ON SPECIFIC DISCHARGE CAPACITY OF LI-ION BATTERIESa bc dFigure 6.17: SEM images of KOHAC (900-2-4) anode: a) Virgin, and after 100 cycles ofcharging and discharging at: b) 500x, c) 1kx, and d) 10Kx.The cells were also subjected to EIS analysis prior to cycling to understand the internalresistances of the cell. The results from EIS analysis (Nyquist plot) are included in Figure6.18. As seen in Figure 6.18 and Table 6.14, Rct was considerably lower for the activatedrCB electrodes when compared to the leached CB sample. This was attributed to the partialgraphitization of the AC samples due to heat treatment as seen in the Raman spectroscopy1396.3. EFFECT OF ACTIVATION EXPERIMENTS OF RCB ON SPECIFIC DISCHARGE CAPACITY OF LI-ION BATTERIESFigure 6.18: EIS test results from activated rCB anodes before cycling experiments (Nyquistplot).analysis (Figure 5.10 and Figure 5.5) and also reduction of diffusion length of Li-ions due toincreased SBET. It was observed that the Rs of KOHAC (900-2-4) sample was higher than theothers. This increase was attributed to the increased electrode resistance of the sample [213].The contact resistance between the electrode and the electrolyte was high due to the presenceof functional groups attached to the sample in combination with the high SBET values, as seenin FTIR analysis of AC samples (indicating the removal of functional groups attached to theAC matrix). Further, TGA analysis was performed to study the presence of surface functionalgroups of activated rCB matrix. The results from this analysis are included in Figure 6.19.Table 6.14: Electrochemical parameters of activated rCB anodes obtained from curve fittingof EIS results.Sample RS (Ω) Cs (F) Rct (Ω) W (Ω) chi sqLeached CB 4.90 2.06 x 10-6 139.40 1.59 x 10-3 0.12±10.3% ±12.0% ±12.2% ±10.8%CO2AC (1000-3) 7.09 1.86 x 10-6 87.50 3.66 x 10-3 0.09±8.9% ±12.8% ±9.7% ±10.4%KOHAC (900-2-4) 24.69 1.61 x 10-6 76.75 5.52 x 10-3 0.04±5.1% ±13.2% ±6.8% ±7.4%1406.3. EFFECT OF ACTIVATION EXPERIMENTS OF RCB ON SPECIFIC DISCHARGE CAPACITY OF LI-ION BATTERIESFigure 6.19: TGA mass loss results from heat treatment of activated rCB samples heated to900°C in N2 gas.As seen in the Figure 6.19, the mass loss of KOH AC (900-2-4) and leached CB samplewas greater than the CO2AC (1000-3) sample. Although both KOH AC (900-2-4), and leachedCB had high concentrations of functional groups attached, the graphitization degree andSBET were responsible for higher capacity from the activated sample. The mass loss fromTGA results was attributed to the presence of volatiles and moisture in the sample. A directcorrelation (proportional relation) of the presence of functional groups, volatiles, andmoisture, with the mass loss during TGA test was observed for all rCB samples tested in thiswork (Appendix C, Figure C.1). Therefore, TGA results further supported the FTIR resultsrevealing presence of additional functional groups attached to the KOH AC (900-2-4) andleached CB samples. The CO2AC (1000-3) sample had the lowest mass loss, indicatinglowest concentration of functional groups (out of the activated rCB samples) in the samples,as was also seen in the FTIR results (Figure 5.4). Since the presence of these groups was seento increase the irreversible capacity loss of the cells, the capacity loss from CO2AC (1000-3)cell was lower than KOH AC (900-2-4) (Table 6.12). It was concluded that the presence offunctional groups on the rCB surface added to the reduction in capacity after first cycle ofcharging and discharging. Further, graphitization in the samples likely had a direct1416.3. EFFECT OF ACTIVATION EXPERIMENTS OF RCB ON SPECIFIC DISCHARGE CAPACITY OF LI-ION BATTERIEScorrelation to the stable specific discharge capacity as well. The reason for this irreversiblecapacity loss was also studied by considering the discharge curves for the first three cyclesof the KOH AC (900-2-4) electrode.Figure 6.20 includes the discharge curves for KOHAC (900-2-4) for the first three cycles.As seen in Figure 6.20, the discharge curve during 1st cycle of discharge for the KOHAC(900-2-4) sample can be divided in three regions consistent with literature [204]. This processis also depicted in Figure 6.27 and will be explained in detail in Section 6.4. After the firstdischarge, the plateau in this curve was not present, and a sloping voltage profile was seenfor subsequent cycling. This further pointed to the formation of a SEI layer on the surface ofthe rCB electrode and irreversible side reactions taking place. It was therefore concluded thatan increase in SBET was responsible for increased capacity of activated rCB cells however, theirreversible capacity drop in these cells was also higher after the first discharge cycle.Figure 6.20: Discharge curves for the first three cycles of KOHAC (900-2-4) anode.1426.3. EFFECT OF ACTIVATION EXPERIMENTS OF RCB ON SPECIFIC DISCHARGE CAPACITY OF LI-ION BATTERIES6.3.2. Activated rCB as additive in LTO anodesFigure 6.21 includes the information from cycling activated rCB doped LTO electrodes.Table 6.15 includes the irreversible capacity loss in activated rCB doped LTO anodes testedin this work. As seen in Figure 6.21a, the highest discharge capacity was obtained from theKOHAC (900-2-4) and CO2AC (1000-3) doped LTO electrode. This high capacity wasexpected from the electrical conductivity and Raman spectroscopy (Figure 5.10 and Figure5.5) results. However, these samples also had a slight drop (<10%) in specific dischargecapacity after the first cycle. This loss was attributed to side reactions with functionalgroups still attached to the activated rCB matrix (Figure 5.4). The high SBET likely resulted inbetter contact between LTO and rCB particles resulting in improved electron transfer andsuperior electrochemical performance of these cells. The reason for this improvement inperformance is further explained in Section 6.4 in detail.Table 6.15: Specific discharge capacity drop of activated rCB doped LTO anodes afterdifferent cycles of charge and discharge.Sample SBET (m2/g)Cycle 1(mAh/g)Cycle 2(mAh/g)Cycle 25(mAh/g)Cycle 50(mAh/g)Leached CB 68 135 127 94 90Super-P 90 123 123 117 116CO2AC (1000-3) 803 163 154 150 150KOHAC (900-2-4) 965 164 149 142 141Figure 6.21b shows the charge-discharge curves for the LTO batteries fabricated withactivated rCB as additives. The polarization when CO2AC (1000-3) electrode was used wasslightly greater than in the case of Super-P electrode likely because of the larger particle sizeof the rCB matrix [199]. This possibly led to areas with limited contact with LTO matrixthereby affecting performance of the anodes. The polarization of KOHAC (900-2-4) additivewas even higher due to increased concentration of functional groups still attached to thematrix as seen in the FTIR results (Figure 5.9b), and the higher ID/IG value (0.92) implyingincreased disorder in KOHAC (900-2-4) sample in comparison to CO2AC (1000-3) (Table 5.4).1436.3. EFFECT OF ACTIVATION EXPERIMENTS OF RCB ON SPECIFIC DISCHARGE CAPACITY OF LI-ION BATTERIESIn order to study the effect of charge rate on specific discharge capacity of the cells, ratetests were performed and the results are included in Figure 6.22 and Table 6.16.abFigure 6.21: Cycling of activated rCB doped LTO anodes at 0.5C: a) Specific dischargecapacity with respect to cycle number, and b) Charge discharge curves.As seen in Figure 6.22, the activated carbon cells performed better than Super-P carbonblack for rates <2 C. This was a result of the higher SBET of the activated rCB samples resultingin increased contact between electrode and rCB additive [214]. However for high rates (2 C),1446.3. EFFECT OF ACTIVATION EXPERIMENTS OF RCB ON SPECIFIC DISCHARGE CAPACITY OF LI-ION BATTERIESthe particle size of the rCB restricted diffusion of Li-ion since no pulverization techniqueswere employed for particle size reduction vs Super-P [199]. Therefore, only for the highdischarge rate of 2 C, Super-P CB outperformed the activated rCB samples. Also, the dischargecapacity was retained for all the cells after rate tests were finished implying stability of theelectrodes.Figure 6.22: Effect of C rate on the specific discharge capacity of activated rCB doped LTOanode.Table 6.16: Specific discharge capacity of activated rCB doped LTO anodes after 10 cyclesfor different C rates.Sample 0.1 C(mAh/g)0.2 C(mAh/g)0.5 C(mAh/g)1 C(mAh/g)2 C(mAh/g)0.1 C(mAh/g)Leached CB 129 118 95 68 36 125CO2AC (1000-3) 159 154 142 121 63 158KOHAC (900-2-4) 177 170 152 122 65 174Super-P 147 143 133 116 87 145EIS analysis was also performed on this electrode to understand the reason for theimproved performance of the activated rCB cells as seen in Figure 6.23. Although mostcurves had a good fit with the modified Randle’s circuit, however, the KOHAC1456.3. EFFECT OF ACTIVATION EXPERIMENTS OF RCB ON SPECIFIC DISCHARGE CAPACITY OF LI-ION BATTERIES(900-2-4+LTO) electrode did not fit well (Appendix C, Figure C.10a). For the sake ofconsistency, the same model was selected and imposed for all circuit cell models, howeverbecause of the high errors associated with the electrochemical parameters obtained fromthis curve fitting, these results are included in the Appendix C, Table C.1, for informationpurposes only. The semi-circle in the Nyquist plot had the minimum radius for the CO2AC(1000-3) electrode, implying minimum Rct, suggesting easy movement of Li-ions across theelectrode. This was likely due to reduced diffusion length as a result of high SBET of theelectrode. Rct was expected to be low for the KOHAC (900-2-4) + LTO electrode however,due to selection of the current model, this value was high. Rs value of the electrodes werecompareable, thereby implying consistency in electrode and electrolyte resistance for thecells.Figure 6.23: EIS test results from activated rCB doped LTO anodes before cyclingexperiments (Nyquist plot).The maximum specific discharge capacity and lowest polarization was observed for theCO2AC (1000-3) + LTO electrode from cycling experiments. Therefore, further analysis wasperformed to understand the reason for this high discharge capacity. The discharge curvesfor the first three cycles of CO2AC (1000-3), when used as an additive for LTO anode, are1466.3. EFFECT OF ACTIVATION EXPERIMENTS OF RCB ON SPECIFIC DISCHARGE CAPACITY OF LI-ION BATTERIESincluded in Figure 6.24. As seen in Figure 6.24, the voltage plateau (at 1.5 V) formed duringdischarging, was directly correlated with Li-ion intercalation in LTO anodes [143]. Also, theloss in discharge capacity for the cells was negligible due to limited functional groups attachedto the activated rCB matrix.Figure 6.24: Discharge curves for the first three cycles of CO2AC (1000-3) doped LTO anode.In order to study the long term effect of cycling on this electrode, EIS analysis was alsoperformed before and after cycling experiments were complete for the CO2AC (1000-3) + LTOcell. The resultant Nyquist plots are included in Figure 6.25. The electrochemical parametersobtained from this curve fitting are included in the Appendix C, Table C.1. The radius ofthe Nyquist plot reduced considerably (indicating reduction in resistances) at the end of thecycling experiments as a result of formation of a stable SEI layer and destruction of passivelayer on the surface of the Li electrode [215]. This indicated reversible intercalation andde-intercalation of Li ions with minimum resistance as desired for commercial LTO anodematerials [216].1476.3. EFFECT OF ACTIVATION EXPERIMENTS OF RCB ON SPECIFIC DISCHARGE CAPACITY OF LI-ION BATTERIESFigure 6.25: EIS analysis of LTO+CO2AC (1000-3) cell before and after cycling experiments.Further, the electrode surface morphology was analyzed using SEM imaging aftercycling. Figure 6.26 includes the SEM images of the CO2AC (1000-3) doped LTO electrodeafter 100 cycles of charge and discharge. No sign of electrolyte decomposition or cracks onthe electrode surface were seen after cycling. This implied stability of the electrode. Similarresults were seen in the other rCB doped LTO electrodes after cycling due to the lowconcentration of carbon additive in the electrode (10 wt%) and are included in Appendix C.It was seen that LTO particles (hexagonal shaped) were coating the rCB substrate, as seen inFigure 6.26 and Figure 6.14. Therefore, larger particle size of the rCB likely reduced themaximum capacity that could be extracted from the samples. Therefore, it was concludedthat the high SBET of activated rCB improved the performance of the cells when used asadditives in LTO anodes.1486.4. MECHANISM OF LITHIATION IN RCB ANODE MATERIALSa bc dFigure 6.26: Structure of CO2AC (1000-3) doped LTO anode before cycling: a) At 500x, b) At10Kx, and after 100 cycles of charging and discharging: c) At 500x, and d) At 10Kx.6.4. Mechanism of lithiation in rCB anode materialsThe mechanism of Li insertion was different in the two different types of cells tested inthis work. When rCB was used as an active material in anode, the rCB was responsible for thecapacity of the cells whereas when rCB was used as an additive, it did not aid in Li-insertion1496.4. MECHANISM OF LITHIATION IN RCB ANODE MATERIALSbut was merely responsible for improving electrical conductivity of the electrode.Li insertion in rCB matrix, when used as an active material in anodes was categorizedinto three distinct stages, as shown in Figure 6.27 (as also reported in the literature fornon-graphitic carbon materials [193, 217]). The first stage was characterized by a slopingdecrease in cell voltage due to the intercalation of Li-ion in between layers of turbostraticcarbon (as seen in discharge curve in Figure 6.20). Due to the random orientation of C layersin turbostratic structure, the voltage was gradually changing instead of a plateau as a resultof continued intercalation (on the surface of micro-graphitic layers and edges) over thevoltage range [193, 217]. The second stage was associated with the SEI formation and sidereactions (reduction) due to functional groups (attached to rCB matrix), and related to theSBET values of the rCB [171, 193, 218]. This was the first plateau region (at 1 V) in Figure6.1b, Figure 6.7b, and Figure 6.15b. This region was not present in the subsequent cycling ofcells (after 1st discharge cycle) further corroborating irreversible reaction with functionalgroups as a main reason for this plateau. The 3rd stage was attributed to the absorption ofLi-ion clusters in nano-pores present in the rCB matrix. Similar phenomena was reported inthe literature and related to diffusion of Li in C [171, 219]. With continued cycling, thefunctional groups irreversibly reacted with the Li-ion, and enabled the closure of nano-pores(due to Li entrapment) resulting in complete removal of stage 2 and reduced area for stage 3after the first discharge cycle. Since SBET change was limited for the raw carbon char,leached CB, and leached + heat samples, (Figure 6.1 and Figure 6.7), the stage 2 was not seendistinctly in the discharge curves of cells made with these materials. Also, the stage 3 wasnot clearly visible (due to low pore volume) in these samples. AC electrodes on the otherhand showed distinct stage 2 and 3 region as seen in their charge-discharge curves (Figure6.15b). Further, the reason for higher discharge capacity values for AC anodes was thedecrease in the Rct of the half cells with increase in area of the porous C as a result ofincreased conduction paths for electron transfer (also seen in the literature [220]).Graphitization in rCB samples could have also lowered the activation energy values for Li1506.4. MECHANISM OF LITHIATION IN RCB ANODE MATERIALSdiffusion [221]. A reduction of polarization of cells was also reported due to thisimprovement in conductivity of the electrodes (improved ID/IG for rCB as seen in Figure 5.5,and Figure 5.10) as also reported in the literature [218]. The porous structure of theelectrode also likely compensated for local volume change in the electrodes making it agood alternative for high capacity C anodes [171, 222].Figure 6.27: Mechanism of lithiation in rCB anodes [223].The discharge capacity of LTO + CO2AC (1000-3) and KOHAC (900-2-4) half cells wasfound to be the highest, and the following Figure 6.28 explains the possible reason for thishigh value. High SBET of the rCB additive not just improved the electrical conductivity ofthe electrodes, as seen in Figure 6.23, but also the ionic conductivity of Li-ions (as a resultof improved electrolyte penetration) as also seen in literature [26, 224, 225]. The electricalcontact between active material and electrolyte was directly improved with the use of highSBET rCB additives [226, 227]. This was also verified by the EIS results (Table C.1) revealinglower values of W for AC cells (vs low SBET cells) further implying easier Li diffusion in theelectrodes. Since, the discharge plateau was only seen at 1.5 V and the cells were tested above1516.5. SUMMARY1 V, the discharge capacitywas believed to be a contribution only from the LTO activematerialand not rCB as also seen in the literature [227]. It should be noted that the volumetric energydensity of the active materials might be compromised due to the porous nature of C additiveas a result of decreased packing density of active material [147]. However, the performanceof activated rCB as an additive in LTO anodes seem promising for stable performance evenat high discharge rates. By virtue of its high SBET, the rCB derived ACs would enhance ionicand electrical conductivities of other commercial electrode systems. Therefore, these ACs canalso be used as additives to other commercial cathode materials including lithium cobalt oxide(LCO), lithium iron phosphate (LFP), nickel manganese cobalt oxide (NMC) etc.Figure 6.28: Mechanism for Li-intercalation in rCB doped LTO anodes.6.5. SummaryThis chapter summarized the use of different grades of rCB in Li-ion systems. Forapplication of rCB as active materials in anodes, the irreversible capacity loss was high forall cells, thus limiting their feasibility for commercial applications. It was observed that1526.5. SUMMARYpurity and graphitization of the rCB, and the SBET had a direct correlation with the specificdischarge capacity and the irreversible capacity loss, respectively. Therefore, leached CB +heat anode had the minimum irreversible capacity loss, due to lack of functional groupsattached to its matrix and high purity. In contrast KOHAC (900-2-4) had the highest specificdischarge capacity due to its high SBET and the higher degree of graphitization. However, allrCB anodes tested have challenges as commercial anode materials due to irreversiblecapacity loss, and Li deposition with continued cycling. rCB showed high potential asadditive materials used in LTO anodes. All samples exhibited low irreversible capacity loss(<10%) with leached CB + heat showing the minimum loss due to its high purity andgraphitization. High SBET rCB samples showed tremendous potential with higher dischargecapacity than commercially used Super-P CB owing to their high surface area, andgraphitization without SEI formation due to the higher voltage employed. Therefore, wastemining tire derived CB showed immense promise as a competitor to commercially availableSuper-P carbon material used commonly in battery applications.153Chapter 7: Conclusions and FutureWork7.1. ConclusionsThis study focused on the processing of raw carbon char obtained from pyrolysis of EOL-OTR tires for energy storage applications. The major conclusions from this study are listedbelow:Chemical leaching1. TEM-EDS, FTIR and XRD analysis revealed the presence of ZnS, SiC and SiO2 phasesin the raw carbon char. Acid leaching was effective in the removal of metallicimpurities. HCl was found to be the most effective in removal of Zn and S due to itshigher dissociation constant. NaOH was found to be more effective in Si removalwhen compared to KOH.2. The skeletal density measurement of the samples had a direct correlation with the ashcontent. Higher density was found for samples with higher ash content due to thepresence of high density elements in ash (predominantly Si).3. 5 M HCl leaching was found to be the most effective for Zn removal with negligableimprovement with further increase in acid concentration to 10 M.4. 10 M NaOH leaching was found to be the most effective in removing Si from the rCBmatrix.1547.1. CONCLUSIONS5. A slurry ratio of 50 g/L was found to be the most effective for chemical leachingexperiments. With further increase in the slurry ratio, the purity of the rCB decreased.6. A leaching time of 2 h was found sufficient for both acid and base leaching experimentswith little or no improvement with longer leaching of the samples.7. A combination of 5 M HCl and 10 M NaOH was found to yield the leached CB withleast impurity concentration.Activation and devolatilization1. KOH activation resulted in higher SBET values when compared to CO2 activation ofleached CB.2. Although the SBET value increased with an increase in temperature and time ofactivation, the micropore volume reduced after a critical value, because of porewidening.3. An SBET of 803 m2/g and 994 m2/g were obtained from activation experiments of rCBwith CO2 and KOH, respectively.4. Functional groups were seen to be attached to the AC matrix indicating the presence ofvolatile components. C=C group was detected in the CO2AC (1000-3) sample whereasC-H, O-H and C=C were detected in the KOHAC (900-2-4) sample.5. Raman spectroscopy revealed graphitization of the samples due to heat treatmentduring activation experiments. The ID/IG ratio was 0.84 and 0.92 for the CO2AC(1000-3) and KOHAC (900-2-4) samples. This was further verified by increasedelectrical conductivity of AC samples.6. A devolatilization experiment at 950 ◦C for 1 h was sufficient for removal of volatileimpurities. This was seen by no change in mass loss with continued heating of thesample after 1 h.1557.1. CONCLUSIONS7. Heating rate directly influenced the time taken to remove volatiles from the leachedCB matrix. A fast heating rate of 25 ◦C/m resulted in incomplete/delayed removal ofvolatiles.8. Leached CB + heat samplewas the samplewithmaximumpurity from all heat treatmentexperiments. This sample had 0.19% volatiles and 1.7% ash still remaining in the samplesin the form of S and Si as detected from the SEM-EDS results.9. Leached CB + heat sample had a low surface area of 76 m2/g with almost nomicroporosity in the sample. FTIR analysis revealed the removal of functional groupsfrom this sample due to almost elimination of the volatiles.Electrochemical testing1. Chemically treated, devolatilized and activated rCB were successfully used as activematerials in anodes and additives to LTO anodes in Li-ion half cells.2. In general, purity, graphitization and surface area had a direct correlation to specificdischarge capacity of cells. An improvement in FC content, and graphitization of rCBdirectly improved the specific discharge capacity of cells because of enhanced electricalconductivity of rCB samples.3. AC samples yielded high irreversible capacity loss (>70%) when used as C anodes.This loss was attributed to its porosity and functional groups attached to rCB matrixpromoting side reactions, as seen from FTIR analysis of AC samples. ACs showedpromising results when used as additives to LTO anodes by improving the electricalconductivity of cells. AC doped LTO anodes outperformed Super-P doped anodes byvirtue of their enhanced ionic conductivity due to their higher SBET values.4. Leached CB + heat sample showed minimum irreversible capacity loss (44% for carbonanode and 8% for LTO anodes) due to its high purity and high electrical conductivity,1567.2. RESEARCH LIMITATIONSas seen in proximate analysis and SEM-EDS analysis experiments.5. A slight increase (<6%) in cell discharge capacity was observed for all rCB anodes. Thiswas because of formation of a unstable SEI with deposition of Li on rCB matrix, as seenin SEM images of electrodes after cycling.7.2. Research limitationsThe following limitations pertaining to the generated results:1. The raw carbon char was manufactured by pyrolysis of mining tires (raw material forthis work). Therefore, optimization of pyrolysis experiments (which would havedirectly affected the raw carbon char properties) were not a part of this work.2. Error in measurement from EDS analysis was considerably high (∼0.7wt%) due toinaccuracies in measurement of low atomic number elements including C and O.Therefore, it was not the most suitable technique for analysis of impurities in the rCBsamples. Consequently, the results from proximate analysis experiments were morereliable.3. Since the ultimate aim of this research was to develop a scalable industry gradeprocess to develop rCB samples, feasibility of the processes was also considered in thedesign of the experiments. Therefore leaching experiments using HF and extremelyhigh temperature heat treatments were avoided.4. Since electrochemical experiments were not the focus of this work, only a few sets ofparameters were tested. Changes to the ratio of rCB to active material would havedirectly made a difference in the results.1577.3. FUTURE WORK7.3. Future workThe following suggestions would help provide additional data to further expand on theresults of this thesis:1. HF leaching experiments and high temperature heat treatment experiments could beperformed to study their effect on purity and graphitization of rCB samples.2. Additional experiments on activation of leached carbon black with CO2 need to beperformed to establish a clear relationship between the effect of processing conditions(temperature, time and concentration of CO2) on the SBET and micropore volume.3. Modification of particle size of the rCB sample may have a direct effect on theelectrochemical behavior of the cells.4. Pre-lithiation of rCB anodes may help in reduction of the irreversible capacity dropafter 1st cycle. However these methods are expensive and time consuming and likelyunfit for commercial applications.5. Coating rCBwith an organic precursor reducing the surface area may result in reducingthe irreversible capacity drop seen in the Li-ion cells.6. Other characterization techniques like in-situ XPS, TEM should be applied to study thechemistry of the SEI layer formed on the rCB surface.158Bibliography[1] D. L. Wood, J. Li, and C. Daniel, “Prospects for reducing the processing cost of lithiumion batteries,” Journal of Power Sources, vol. 275, pp. 234–242, feb 2015.[2] I. Cho, J. Choi, K. Kim, M. H. Ryou, and Y. M. Lee, “A comparative investigation ofcarbon black (Super-P) and vapor-grown carbon fibers (VGCFs) as conductive additivesfor lithium-ion battery cathodes,” RSC Advances, vol. 5, pp. 95073–95078, nov 2015.[3] B. Diouf and R. Pode, “Potential of lithium-ion batteries in renewable energy,” apr 2015.[4] Y.-R. Lin and H. Teng, “Mesoporous carbons from waste tire char and their applicationin wastewater discoloration,” Microporous and Mesoporous Materials, vol. 54, pp. 167–174, jul 2002.[5] A. Aranda, R. Murillo, T. García, M. M. Callén, and A. A. Mastral, “Steam activation oftyre pyrolytic carbon black: Kinetic study in a thermobalance,” Chemical EngineeringJournal, vol. 126, pp. 79–85, feb 2007.[6] P. Lahijani, Z. A. Zainal, A. R. Mohamed, and M. Mohammadi, “Co-gasification oftire and biomass for enhancement of tire-char reactivity in CO2 gasification process,”Bioresource Technology, vol. 138, pp. 124–130, jun 2013.[7] J. Han, W. Li, D. Liu, L. Qin, W. Chen, and F. Xing, “Pyrolysis characteristic andmechanism of waste tyre: A thermogravimetry-mass spectrometry analysis,” Journalof Analytical and Applied Pyrolysis, vol. 129, pp. 1–5, jan 2018.[8] M. Wojtowicz and M. Serio, “Pyrolysis of scrap tires: Can it be profitable?,” Chemtech,vol. 26, p. 48, 1996.[9] M. J. Matheson, T. P. Wampler, and W. J. Simonsick, “The effect of carbon-black filling159Bibliographyon the pyrolysis behavior of natural and synthetic rubbers,” Journal of Analytical andApplied Pyrolysis, vol. 29, pp. 129–136, aug 1994.[10] Industry Experts Report, “Carbon Black - A Global Market Overview,” tech. rep.,Industry Experts, 2016.[11] H. Marsh and F. Rodriéguez-Reinoso, Activated carbon. Elsevier, 2006.[12] A. Pehlken and E. Essadiqi, “Scrap Tire Recycling in Canada A reference for all partiesinvolved in the tire recycling industry on the options available for end-of-life OTRand passenger tires from an economic and environmental perspective,” tech. rep.,CANMET-Materials Technology Laboratory, 2005.[13] IVL Swedish Environmental Research Institute, “Scandinavian Enviro Systems,” tech.rep., Scandinavian Enviro Systems, 2019.[14] M. Endo, C. Kim, K. Nishimura, T. Fujino, and K. Miyashita, “Recent development ofcarbon materials for Li ion batteries,” Carbon, vol. 38, pp. 183–197, jan 2000.[15] Edward Buiel, Li insertion in hard carbon anode materials fo Li ion batteries. PhD thesis,Dalhousie University, 1998.[16] G. R. R. Jr., J. M. Hammarstrom, and D. W. Olson, “Critical mineral resources of theUnited States—Economic and environmental geology and prospects for future supply:U.S. Geological Survey Professional Paper,” tech. rep., USGS, 2017.[17] E. M. Dannenberg, L. Paquin, and H. Gwinnell, “Carbon Black,” in Kirk-OthmerEncyclopedia of Chemical Technology, Wiley, dec 2000.[18] N. Cardona, F. Campuzano, M. Betancur, L. Jaramillo, and J. D. Martínez, “Possibilitiesof carbon black recovery from waste tyre pyrolysis to be used as additive in rubbergoods-a review,” in IOP Conference Series: Materials Science and Engineering, p. 012012,IOP Publishing, 2018.160Bibliography[19] M. E. Spahr and R. Rothon, Carbon Black as a Polymer Filler. Springer, 2015.[20] O. A. Al-Hartomy, F. Al-Solamy, A. Al-Ghamdi, N. Dishovsky, M. Ivanov, M. Mihaylov,and F. El-Tantawy, “Influence of carbon black structure and specific surface area on themechanical and dielectric properties of filled rubber composites,” International Journalof Polymer Science, vol. 2011, 2011.[21] J. C. Huang, “Carbon black filled conducting polymers and polymer blends,” dec 2002.[22] G. Kühner and M. Voll, “Manufacture of Carbon Black,” in Carbon Black, pp. 1–66,Taylor & Francis, 2018.[23] W. M. Hess and C. R. Herd, “Microstructure, Morphology and General PhysicalProperties,” in Carbon Black, pp. 89–173, Taylor & Francis, 2018.[24] D. Pantea, H. Darmstadt, S. Kaliaguine, and C. Roy, “Electrical conductivity ofconductive carbon blacks: influence of surface chemistry and topology,”Applied SurfaceScience, vol. 217, pp. 181–193, jul 2003.[25] H. B. Lin, W. Z. Huang, H. B. Rong, J. N. Hu, S. W. Mai, L. D. Xing, M. Q. Xu, X. P. Li,andW. S. Li, “Surface natures of conductive carbon materials and their contributions tocharge/discharge performance of cathodes for lithium ion batteries,” Journal of PowerSources, vol. 287, pp. 276–282, aug 2015.[26] V. Palomares, A. Goñi, I. G. De Muro, I. De Meatza, M. Bengoechea, I. Cantero, andT. Rojo, “Conductive additive content balance in Li-ion battery cathodes: Commercialcarbon blacks vs. in situ carbon from LiFePO4/C composites,” Journal of Power Sources,vol. 195, pp. 7661–7668, nov 2010.[27] J. Svoboda, V. Vaclavik, T. Dvorsky, L. Klus, and R. Zajac, “The potential utilization ofthe rubber material after waste tire recycling,” in IOP conference series: materials scienceand engineering., 2018.161Bibliography[28] G. Díaz-Ferrán, D. Chudinzow, W. Kracht, and L. Eltrop, “Solar-powered pyrolysis ofscrap rubber frommining truck end-of-life tires-A case study for themining industry inthe Atacama Desert, Chile,” inAIP Conference Proceedings, vol. 2033, p. 20002, AmericanInstitute of Physics Inc., nov 2018.[29] D. Czajczyńska, K. M. Czajka, R. Krzyzyńska, and H. Jouhara, “Experimental analysisof waste tyres as a sustainable source of energy,” in E3S Web of Conferences, vol. 100,p. 00012, EDP Sciences, jun 2019.[30] R. Murillo, M. Navarro, J. López, E. Aylón, M. S. Callén, G. Tomás, and A. M. Mastral,“Kinetic Model Comparison for Waste Tire Char Reaction with CO2,” Industrial &Engineering Chemistry Research, vol. 43, no. 24, pp. 7768–7773, 2004.[31] A. M. Cunliffe and P. T. Williams, “Influence of Process Conditions on the Rate ofActivation of Chars Derived from Pyrolysis of Used Tires,” Energy & Fuels, pp. 166–175, 1999.[32] A. Oberlin, “Carbonization and Graphitization,” Carbon, vol. 22, no. 6, p. 541, 1984.[33] R. B. González-González, L. T. González, S. Iglesias-González, E. González-González,S. O. Martinez-Chapa, M. Madou, M. M. Alvarez, and A. Mendoza, “Characterization ofchemically activated pyrolytic carbon black derived from waste tires as a candidate fornanomaterial precursor,” Nanomaterials, vol. 10, pp. 1–22, nov 2020.[34] Z. Czigány and L. Hultman, “Interpretation of electron diffraction patterns fromamorphous and fullerene-like carbon allotropes,” Ultramicroscopy, vol. 110, pp. 815–819, jun 2010.[35] R. Gómez-Hernández, Y. Panecatl-Bernal, and M. Á. Méndez-Rojas, “High yield andsimple one-step production of carbon black nanoparticles from waste tires,” Heliyon,vol. 5, p. e02139, jul 2019.162Bibliography[36] K. Jurkiewicz, M. Pawlyta, and A. Burian, “Structure of Carbon Materials Exploredby Local Transmission Electron Microscopy and Global Powder Diffraction Probes,”Journal of Carbon Research, vol. 4, p. 68, dec 2018.[37] C. Wang, D. Li, T. Zhai, H. Wang, Q. Sun, and H. Li, “Direct conversion of waste tiresinto three-dimensional graphene,” Energy Storage Materials, vol. 23, pp. 499–507, dec2019.[38] Z. Jankovská, M. Večeř, I. Koutník, and L. Matějová, “A Case Study of Waste ScrapTyre-Derived Carbon Black Tested for Nitrogen, Carbon Dioxide, and CyclohexaneAdsorption,” Molecules, vol. 25, p. 4445, sep 2020.[39] M. Keiluweit, P. S. Nico, M. Johnson, and M. Kleber, “Dynamic molecular structure ofplant biomass-derived black carbon (biochar),” Environmental Science and Technology,vol. 44, no. 4, pp. 1247–1253, 2010.[40] Y. Han, P.-P. Zhao, X.-T. Dong, C. Zhang, and S.-X. Liu, “Improvement inelectrochemical capacitance of activated carbon from scrap tires by nitric acidtreatment,” Frontiers of Materials Science, vol. 8, pp. 391–398, dec 2014.[41] H. Teng, M. A. Serio, M. A. W6jtowicz, R. Bassilakis, and P. R. Solomon, “Reprocessingof Used Tires into Activated Carbon and Other Products,” Ind. Eng. Chem. Res, vol. 34,pp. 3102–3111, 1995.[42] G. I. Danmaliki and T. A. Saleh, “Influence of conversion parameters of waste tiresto activated carbon on adsorption of dibenzothiophene from model fuels,” Journal ofCleaner Production, vol. 117, pp. 50–55, mar 2016.[43] V. Gupta, B. Gupta, A. Rastogi, S. Agarwal, and A. Nayak, “A comparative investigationon adsorption performances of mesoporous activated carbon prepared from wasterubber tire and activated carbon for a hazardous azo dye—Acid Blue 113,” Journal ofHazardous Materials, vol. 186, pp. 891–901, feb 2011.163Bibliography[44] M. R. Nunes, G. M. Perez, L. F. Loguercio, E. W. Alves, N. L. V. Carreño, J. L. Martins,and I. T. S. Garcia, “Active carbon preparation from treads of tire waste for dye removalin waste water,” Journal of the Brazilian Chemical Society, vol. 22, pp. 2027–2035, nov2011.[45] H. Teng, Y.-C. Lin, and L.-Y. Hsu, “Production of Activated Carbons from Pyrolysisof Waste Tires Impregnated with Potassium Hydroxide,” Journal of the Air & WasteManagement Association, vol. 50, pp. 1940–1946, nov 2000.[46] E. Manchón-Vizuete, A. Macías-García, A. Nadal Gisbert, C. Fernández-González, andV. Gómez-Serrano, “Adsorption of mercury by carbonaceous adsorbents prepared fromrubber of tyre wastes,” Journal of Hazardous Materials, vol. 119, pp. 231–238, mar 2005.[47] M. Gogoi, R. K. Layek, J. Vuorinen, and M. Mahato, “Conversion of Solid Waste intoFunctional Carbon Materials: A Review,” Energy and Environment Focus, vol. 6, pp. 52–68, mar 2017.[48] R. Murillo, M. V. Navarro, T. García, J. M. López, M. S. Callén, E. Aylón, and A. M.Mastral, “Production and Application of Activated Carbons Made from Waste Tire,”Ind. Eng. Chem. Res., vol. 44, no. 18, pp. 7228–7233, 2005.[49] P. Hadi, K. Y. Yeung, J. Guo, H. Wang, and G. McKay, “Sustainable development oftyre char-based activated carbons with different textural properties for value-addedapplications,” Journal of Environmental Management, vol. 170, pp. 1–7, apr 2016.[50] Z. Koreňová, M. Juma, J. Annus, J. Markoš, and L. Jelemenský, “Kinetics of pyrolysisand properties of carbon black from a scrap tire,” Chemical Papers, vol. 60, pp. 422–426,jan 2006.[51] I. Ali, “The Quest for Active Carbon Adsorbent Substitutes: Inexpensive Adsorbents forToxic Metal Ions Removal fromWastewater,” Separation & Purification Reviews, vol. 39,pp. 95–171, nov 2010.164Bibliography[52] M. A. Yahya, Z. Al-Qodah, and C. Z. Ngah, “Agricultural bio-waste materials aspotential sustainable precursors used for activated carbon production: A review,”Renewable and Sustainable Energy Reviews, vol. 46, pp. 218–235, jun 2015.[53] T. A. Saleh and G. I. Danmaliki, “Adsorptive desulfurization of dibenzothiophene fromfuels by rubber tyres-derived carbons: Kinetics and isotherms evaluation,” ProcessSafety and Environmental Protection, vol. 102, pp. 9–19, 2016.[54] J. Shah, M. R. Jan, F. Mabood, and M. Shahid, “Conversion of Waste Tyres into CarbonBlack and their Utilization as Adsorbent,” Journal of the Chinese Chemical Society,vol. 53, pp. 1085–1089, oct 2006.[55] G.-G. Choi, S.-H. Jung, S.-J. Oh, and J.-S. Kim, “Total utilization of waste tire rubberthrough pyrolysis to obtain oils and CO2 activation of pyrolysis char,” Fuel ProcessingTechnology, vol. 123, pp. 57–64, jul 2014.[56] T. A. Saleh and G. I. Danmaliki, “Influence of acidic and basic treatments of activatedcarbon derived from waste rubber tires on adsorptive desulfurization of thiophenes,”Journal of the Taiwan Institute of Chemical Engineers, vol. 60, pp. 460–468, mar 2016.[57] P. Ariyadejwanich, W. Tanthapanichakoon, K. Nakagawa, S. R. Mukai, and H. Tamon,“Preparation and characterization of mesoporous activated carbon from waste tires,”Carbon, vol. 41, pp. 157–164, jan 2003.[58] M. Arabiourrutia, G. Lopez, G. Elordi, M. Olazar, R. Aguado, and J. Bilbao, “Productdistribution obtained in the pyrolysis of tyres in a conical spouted bed reactor,”Chemical Engineering Science, vol. 62, pp. 5271–5275, 2007.[59] T. Kotkowski, R. Cherbański, and E. Molga, “Acetone adsorption on CO2-activatedtyre pyrolysis char – Thermogravimetric analysis,” Chemical and process engineering.,vol. 39, no. 2, pp. 233–246, 2018.165Bibliography[60] E. L. Mui, W. Cheung, M. Valix, and G. McKay, “Mesoporous activated carbonfrom waste tyre rubber for dye removal from effluents,” Microporous and MesoporousMaterials, vol. 130, pp. 287–294, may 2010.[61] R. Acosta, C. Tavera, P. Gauthier-Maradei, and D. Nabarlatz, “Production of Oiland Char by Intermediate Pyrolysis of Scrap Tyres: Influence on Yield and ProductCharacteristics,” International Journal of Chemical Reactor Engineering, vol. 13, pp. 189–200, jan 2015.[62] J. Sun, T. A. Brady, M. J. Rood, M. Rostam-Abadi, and A. A. Lizzio, “Adsorbed natural gasstorage with activated carbon.,” Preprints of Papers, American Chemical Society, Divisionof Fuel Chemistry, vol. 41, p. 960376, 1996.[63] M. Zhi, F. Yang, F. Meng, M. Li, A. Manivannan, and N. Wu, “Effects of Pore Structureon Performance of AnActivated-Carbon Supercapacitor Electrode Recycled from ScrapWaste Tires,” ACS Sustainable Chem. Eng., pp. 1592–1598, 2014.[64] A. S. Al-Rahbi and P. T. Williams, “Production of activated carbons from waste tyresfor low temperature NOx control,” Waste Management, vol. 49, pp. 188–195, mar 2016.[65] A. Nieto-Márquez, E. Atanes, J. Morena, F. Fernández-Martínez, and J. L. Valverde,“Upgrading waste tires by chemical activation for the capture of SO2,” Fuel ProcessingTechnology, vol. 144, pp. 274–281, apr 2016.[66] A. Nieto-Márquez, A. Pinedo-Flores, G. Picasso, E. Atanes, and R. Sun Kou, “Selectiveadsorption of Pb2+, Cr3+ and Cd2+mixtures on activated carbons prepared fromwastetires,” Journal of Environmental Chemical Engineering, vol. 5, pp. 1060–1067, feb 2017.[67] A. Zabaniotou, P. Madau, P. Oudenne, C. Jung, M.-P. Delplancke, and A. Fontana,“Active carbon production from used tire in two-stage procedure: industrial pyrolysisand bench scale activation with H2O–CO2 mixture,” Journal of Analytical and AppliedPyrolysis, vol. 72, pp. 289–297, nov 2004.166Bibliography[68] J. F. González, J. M. Encinar, C. M. González-García, E. Sabio, A. Ramiro, J. L. Canito,and J. Gañán, “Preparation of activated carbons from used tyres by gasification withsteam and carbon dioxide,” Applied Surface Science, vol. 252, pp. 5999–6004, jun 2006.[69] A. Molino, A. Erto, F. D. Natale, A. Donatelli, P. Iovane, and D. Musmarra, “Gasificationof Granulated Scrap Tires for the Production of Syngas and a Low-Cost Adsorbent forCd(II) Removal fromWastewaters,” Industrial & Engineering Chemistry Research, vol. 52,pp. 12154–12160, aug 2013.[70] M. Alexandre-Franco, C. Fernández-González, M. Alfaro-Domínguez, and V. Gómez-Serrano, “Adsorption of cadmium on carbonaceous adsorbents developed from usedtire rubber,” Journal of Environmental Management, vol. 92, pp. 2193–2200, sep 2011.[71] K. M. Dimpe, J. C. Ngila, and P. N. Nomngongo, “Application of waste tyre-basedactivated carbon for the removal of heavy metals in wastewater,” Cogent Engineering,vol. 4, may 2017.[72] S. Seng-eiad and S. Jitkarnka, “Untreated and HNO3-treated pyrolysis char as catalystsfor pyrolysis of waste tire: In-depth analysis of tire-derived products and charcharacterization,” Journal of Analytical and Applied Pyrolysis, vol. 122, 2016.[73] A. Sirimuangjinda, D. Atong, and C. Pechyen, “Comparison on Pore Development ofActivated Carbon Produced from Scrap Tire by Hydrochloric Acid and Sulfuric Acid,”in Advanced Materials Research, pp. 706–710, 2013.[74] P. Zhao, Y. Han, X. Dong, C. Zhang, and S. Liu, “Application of Activated CarbonsDerived from Scrap Tires as Electrode Materials for Supercapacitors,” ECS Journal ofSolid State Science and Technology, vol. 4, no. 7, pp. 35–40, 2015.[75] J.-H. Lin and S.-B. Wang, “An effective route to transform scrap tire carbons intohighly-pure activated carbons with a high adsorption capacity of ethylene blue through167Bibliographythermal and chemical treatments,” Environmental Technology & Innovation, vol. 8,pp. 17–27, nov 2017.[76] I. Iraola-Arregui, P. Van Der Gryp, and J. F. Görgens, “A review on the demineralisationof pre- and post-pyrolysis biomass and tyre wastes,” Waste Management, vol. 79,pp. 667–688, sep 2018.[77] R. Kumar and A. Sharma, “Morphologically tailored activated carbon derived fromwaste tires as high-performance anode for Li-ion battery,” Journal of AppliedElectrochemistry, vol. 48, pp. 1–13, jan 2018.[78] S. Manocha, G. R. Prasad, P. Joshi, R. S. Zala, S. S. Gokhale, and L. M. Manocha,“Preparation and characterization of activated carbon from demineralized tyre char,”in AIP Conference Proceedings, vol. 1538, pp. 109–112, 2013.[79] M. Issac, B. Dai, and L. Zhang, “Kinetics underpinning the C-CO2 gasification ofwaste tyre char and its interaction with coal char upon co-gasification,” Fuel, vol. 256,p. 115991, nov 2019.[80] J. P. Chen and S. Wu, “Acid/Base-Treated Activated Carbons: Characterization ofFunctional Groups and Metal Adsorptive Properties,” Langmuir, vol. 20, pp. 2233–2242,2004.[81] V. Gupta, B. Gupta, A. Rastogi, S. Agarwal, and A. Nayak, “Pesticides removal fromwaste water by activated carbon prepared from waste rubber tire,” Water Research,vol. 45, pp. 4047–4055, jul 2011.[82] H. O. Pierson, Handbook of Carbon, Graphite, Diamond and Fullerenes Properties,Processing and Applications. Noyes Publications, 1993.[83] A. Pandolfo and A. Hollenkamp, “Carbon properties and their role in supercapacitors,”Journal of Power Sources, vol. 157, pp. 11–27, jun 2006.168Bibliography[84] T. A. Saleh and V. K. Gupta, “Processing methods, characteristics and adsorptionbehavior of tire derived carbons: A review,” Advances in Colloid and Interface Science,vol. 211, pp. 93–101, sep 2014.[85] T. Wigmans, “Industrial aspects of production and use of activated carbons,” Carbon,vol. 27, pp. 13–22, jan 1989.[86] B. Acevedo and C. Barriocanal, “Texture and surface chemistry of activated carbonsobtained from tyre wastes,” Fuel Processing Technology, vol. 134, pp. 275–283, jun 2015.[87] F. Rodríguez-Reinoso, M. Molina-Sabio, and M. González, “The use of steam and CO2as activating agents in the preparation of activated carbons,” Carbon, vol. 33, pp. 15–23,jan 1995.[88] S. Ryu, H. Jin, D. Gondy, N. Pusset, and P. Ehrburger, “Activation of carbon fibres bysteam and carbon dioxide,” Carbon, vol. 31, no. 5, pp. 841–842, 1993.[89] M. Molina-Sabio, M. Gonzalez, F. Rodriguez-Reinoso, and A. Sepúlveda-Escribano,“Effect of steam and carbon dioxide activation in the micropore size distribution ofactivated carbon,” Carbon, vol. 34, pp. 505–509, jan 1996.[90] A. Quek and R. Balasubramanian, “Low-Energy and Chemical-Free Activation ofPyrolytic Tire Char and Its Adsorption Characteristics,” Journal of the Air & WasteManagement Association, vol. 59, no. 6, pp. 747–756, 2009.[91] E. Moaseri, M. Karimi, S. Kiani, and A. Ahmadpour, “Effect of pretreatment processon the characteristics of activated carbons produced from chemical activation of scraptire,” Environmental Progress & Sustainable Energy, vol. 36, pp. 796–801, may 2017.[92] R. Acosta, V. Fierro, A. Martinez de Yuso, D. Nabarlatz, and A. Celzard, “Tetracyclineadsorption onto activated carbons produced by KOH activation of tyre pyrolysis char,”Chemosphere, vol. 149, pp. 168–176, apr 2016.169Bibliography[93] K. M. Rambau, N. M. Musyoka, and H. W. Langmi, “Mechanochemical approach in thesynthesis of activated carbons from waste tyres and its hydrogen storage applications,”Materials Today: Proceedings, vol. 5, pp. 10505–10513, jan 2018.[94] N. Antoniou, G. Stavropoulos, and A. Zabaniotou, “Activation of end of life tyrespyrolytic char for enhancing viability of pyrolysis - Critical review, analysis andrecommendations for a hybrid dual system,” Renewable and Sustainable Energy Reviews,vol. 39, pp. 1053–1073, nov 2014.[95] J. H. Um, C. Y. Ahn, J. Kim, M. Jeong, Y. E. Sung, Y. H. Cho, S. S. Kim, and W. S. Yoon,“From grass to battery anode: Agricultural biomass hemp-derived carbon for lithiumstorage,” RSC Advances, vol. 8, no. 56, pp. 32231–32240, 2018.[96] J. Ou, L. Yang, and Z. Zhang, “Chrysanthemum derived hierarchically porous nitrogen-doped carbon as high performance anode material for Lithium/Sodium ion batteries,”Powder Technology, 2018.[97] L. Tao, Y. Huang, X. Yang, Y. Zheng, C. Liu, M. Di, and Z. Zheng, “Flexibleanode materials for lithium-ion batteries derived from waste biomass-based carbonnanofibers: I. Effect of carbonization temperature,” RSC Advances, vol. 8, no. 13,pp. 7102–7109, 2018.[98] Y. Gong, D. Li, C. Luo, Q. Fu, and C. Pan, “Highly porous graphitic biomass carbonas advanced electrode materials for supercapacitors,” Green Chemistry, vol. 19, no. 17,pp. 4132–4140, 2017.[99] B. Wang, Y. Wang, Y. Peng, X. Wang, N. Wang, J. Wang, and J. Zhao, “Nitrogen-doped biomass-based hierarchical porous carbon with large mesoporous volume forapplication in energy storage,” Chemical Engineering Journal, vol. 348, pp. 850–859, sep2018.170Bibliography[100] S.-Y. Tsai, R. Muruganantham, S.-H. Tai, B. K. Chang, S.-C. Wu, Y.-L. Chueh, and W.-R.Liu, “Coffee grounds-derived carbon as high performance anode materials for energystorage applications,” Journal of the Taiwan Institute of Chemical Engineers, vol. 97,pp. 178–188, 2019.[101] J. H. Um, Y. Kim, C.-Y. Ahn, J. Kim, Y.-E. Sung, Y.-H. Cho, S.-S. Kim, and W.-S.Yoon, “Biomass Waste, Coffee Grounds-derived Carbon for Lithium Storage,” Journalof Electrochemical Science and Technology, vol. 9, no. 3, pp. 163–168, 2018.[102] N. K. Chaudhari, D. Bhattacharjya, H. Kim, J.-S. Yu, N. K. Chaudhari, and W.-J.Chung, “N-Carbon from Waste Tea as Efficient Anode Electrode Material in LithiumIon Batteries Oxygen reduction reaction View project Development of ionic liquidsupported nanocomposites for simultaneous capture and conversion of carbon dioxideView project N-Car,” Article in Journal of Nanoscience and Nanotechnology, vol. 17,pp. 1838–1846, 2017.[103] J. S. Gnanaraj, R. J. Lee, A. M. Levine, J. L. Wistrom, S. L. Wistrom, Y. Li, J. Li, K. Akato,A. K. Naskar, and M. Parans Paranthaman, “Sustainable Waste Tire Derived CarbonMaterial as a Potential Anode for Lithium-Ion Batteries,” Sustainability, vol. 10, no. 8,p. 2840, 2018.[104] Z. Li, Z. Xu, X. Tan, H. Wang, C. M. B. Holt, T. Stephenson, B. C. Olsen, andD. Mitlin, “Mesoporous nitrogen-rich carbons derived from protein for ultra-highcapacity battery anodes and supercapacitors,” Energy and Environment Science, vol. 6,p. 871, 2013.[105] B. T. Mekonnen, A. Meiyazhagan, M. Ragothaman, C. Kalirajan, and T. Palanisamy,“Bi-functional iron embedded carbon nanostructures from collagen waste forphotocatalysis and Li-ion battery applications: A waste to wealth approach,” Journal ofCleaner Production, vol. 210, pp. 190–199, 2019.171Bibliography[106] S. Villagómez-Salas, P. Manikandan, S. F. Acuña Guzmán, and V. G. Pol,“Amorphous Carbon Chips Li-Ion Battery Anodes Produced through PolyethyleneWaste Upcycling,” ACS Omega, vol. 3, pp. 17520–17527, dec 2018.[107] J. Zhu, S. Liu, Y. Liu, T. Meng, L. Ma, H. Zhang, M. Kuang, and J. Jiang, “Graphitic,Porous, and Multiheteroatom Codoped Carbon Microtubes Made from Hair Waste: ASuperb and Sustained Anode Substitute for Li-Ion Batteries,”ACS Sustainable Chemistry& Engineering, vol. 6, pp. 13662–13669, nov 2018.[108] A. K. Naskar, Z. Bi, Y. Li, S. K. Akato, D. Saha, M. Chi, C. A. Bridges, andM. P. Paranthaman, “Tailored recovery of carbons from waste tires for enhancedperformance as anodes in lithium-ion batteries,” RSC Advances, vol. 4, p. 38213, aug2014.[109] M. Parans Paranthaman, “Economically Viable "Green" Carbon Anodes for Lithium-IonBatteries from Recycled Scrap Tires,” tech. rep., Oak Ridge Laboratory, 2017.[110] J. Sun, T. A. Brady, M. J. Rood, C.M. Lehmann, Massoud Rostam-Abadi, and A. A. Lizzio,“Adsorbed Natural Gas Storage with Activated Carbons Made from Illinois Coals andScrap Tires,” Energy & Fuels, vol. 11, no. 2, pp. 316–322, 1997.[111] L. Li, S. Liu, and T. Zhu, “Application of activated carbon derived from scrap tires foradsorption of Rhodamine B,” Journal of Environmental Sciences, vol. 22, no. 8, pp. 1273–1280, 2010.[112] G. López, M. Olazar, M. Artetxe, M. Amutio, G. Elordi, and J. Bilbao, “Steam activationof pyrolytic tyre char at different temperatures,” Journal of Analytical and AppliedPyrolysis, vol. 85, pp. 539–543, may 2009.[113] Q. Ren, Z. Wu, S. Hu, L. He, S. Su, Y. Wang, L. Jiang, and J. Xiang, “Sulfur self-doped char with high specific capacitance derived from waste tire: Effects of pyrolysistemperature,” Science of the Total Environment, vol. 741, p. 140193, nov 2020.172Bibliography[114] R. Kumar, T. Bhuvana, and A. Sharma, “Tire Waste Derived Turbostratic Carbon asan Electrode for a Vanadium Redox Flow Battery,” in ACS Sustainable Chemistry andEngineering, vol. 105, pp. 161–169, American Chemical Society, jul 2018.[115] Y. Li, M. P. Paranthaman, K. Akato, A. K. Naskar, A. M. Levine, R. J. Lee, S.-O. Kim,J. Zhang, S. Dai, and A.Manthiram, “Tire-derived carbon composite anodes for sodium-ion batteries,” Journal of Power Sources, vol. 316, pp. 232–238, jun 2016.[116] P. Lavela, P. L. Tirado, Ricardo Alcántara, C. Pérez-Vicente, J. L., and P. Lavela, “AnodeMaterials for Lithium-Ion Batteries,” Li ion batteries - Advanced materials technology,pp. 97–146, 2011.[117] E. Zhecheva, R. Stoyanova, J. M. Jiménez-Mateos, R. Alcántara, P. Lavela, and J. L.Tirado, “EPR study on petroleum cokes annealed at different temperatures and used inlithium and sodium batteries,” Carbon, vol. 40, pp. 2301–2306, jan 2002.[118] D. A. Stevens and J. R. Dahn, “HighCapacity AnodeMaterials for Rechargeable Sodium-Ion Batteries,” Journal of The Electrochemical Society, vol. 147, p. 1271, apr 2000.[119] H. Gong, D. Wang, Y. Jiang, L. Wang, K. Zhang, and Y. Qian, “Phosphorus-dopedmesoporous carbon derived from waste tires as anode for K-ion batteries,” MaterialsLetters, vol. 285, p. 128983, feb 2021.[120] Y. Wang, Y. Li, S. S. Mao, D. Ye, W. Liu, R. Guo, Z. Feng, J. Kong, and J. Xie, “N-doped porous hard-carbon derived from recycled separators for efficient lithium-ionand sodium-ion batteries,” Sustainable Energy and Fuels, vol. 3, no. 3, pp. 717–722, 2019.[121] Y. Li, R. A. Adams, A. Arora, V. G. Pol, A. M. Levine, R. J. Lee, K. Akato, A. K. Naskar, andM. P. Paranthaman, “Sustainable Potassium-Ion Battery Anodes Derived from Waste-Tire Rubber,” Journal of The Electrochemical Society, vol. 164, pp. A1234–A1238, apr2017.173Bibliography[122] M. Palanisamy, V. G. Pol, S. F. Evans, B. Kia Jackson, C. J. Jafta, C. A. Bridges, S. Dai,A. M. Levine, R. J. Lee, and M. Parans Paranthaman, “Encapsulated Sb and Sb 2 O3 particles in waste-tire derived carbon as stable composite anodes for sodium-ionbatteries,” Sustainable and Energy Fuels, vol. 4, pp. 3613–3622, 2020.[123] L. Zhen, Sajid Bashir, Jingbo Louise, Nanostructured Materials for Next-GenerationEnergy Storage and Conversion Advanced Battery and Supercapacitors. Springer, 2019.[124] C. Liu, Z. G. Neale, and G. Cao, “Understanding electrochemical potentials of cathodematerials in rechargeable batteries,” mar 2016.[125] N. Nitta, F. Wu, J. T. Lee, and G. Yushin, “Li-ion battery materials: Present and future,”jun 2015.[126] N. Mahmood, T. Tang, and Y. Hou, “Nanostructured Anode Materials for Lithium IonBatteries: Progress, Challenge and Perspective,” sep 2016.[127] J. Cabana, L. Monconduit, D. Larcher, and M. R. Palacín, “Beyond intercalation-basedLi-ion batteries: The state of the art and challenges of electrode materials reactingthrough conversion reactions,” Advanced Materials, vol. 22, pp. E170–E192, sep 2010.[128] D. Deng, “Li-ion batteries: Basics, progress, and challenges,” sep 2015.[129] Z. Ogumi and H. Wang, “Carbon anode materials,” in Lithium-Ion Batteries: Science andTechnologies, pp. 49–73, Springer New York, 2009.[130] V. Etacheri, R. Marom, R. Elazari, G. Salitra, and D. Aurbach, “Challenges in thedevelopment of advanced Li-ion batteries: A review,” sep 2011.[131] D. Aurbach, Y. Ein-Eli, O. Chusid, Y. Carmeli, M. Babai, and H. Yamin, “The CorrelationBetween the Surface Chemistry and the Performance of Li-Carbon IntercalationAnodes for Rechargeable "Rocking-Chair" Type Batteries,” J. Electrochern. Soc, vol. 141,no. 3, pp. 603–611, 1994.174Bibliography[132] L. Ji, Z. Lin, M. Alcoutlabi, and X. Zhang, “Recent developments in nanostructuredanode materials for rechargeable lithium-ion batteries,” aug 2011.[133] P. Verma, P. Maire, and P. Novák, “A review of the features and analyses of the solidelectrolyte interphase in Li-ion batteries,” sep 2010.[134] D. Aurbach, B. Markovsky, I. Weissman, E. Levi, and Y. Ein-Eli, “On the correlationbetween surface chemistry and performance of graphite negative electrodes for Li ionbatteries,” Electrochimica Acta, vol. 45, pp. 67–86, sep 1999.[135] R. A. Huggins, Advanced batteries: Materials science aspects. Springer, 2009.[136] T. Hang, D. Mukoyama, H. Nara, N. Takami, T. Momma, and T. Osaka, “Electrochemicalimpedance spectroscopy analysis for lithium-ion battery using Li4Ti5O12 anode,”Journal of Power Sources, vol. 222, pp. 442–447, jan 2013.[137] T. Nordh, Lithium titanate as anode material in lithium-ion batteries-A surface study.PhD thesis, Uppsala University, 2015.[138] L. Yu, H. B. Wu, and X. W. Lou, “Mesoporous Li4Ti5O12 hollow spheres with enhancedlithium storage capability,” Advanced Materials, vol. 25, pp. 2296–2300, apr 2013.[139] H. Ge, L. Chen,W. Yuan, Y. Zhang, Q. Fan, H. Osgood, D.Matera, X.M. Song, andG.Wu,“Unique mesoporous spinel Li4Ti5O12 nanosheets as anode materials for lithium-ionbatteries,” Journal of Power Sources, vol. 297, pp. 436–441, nov 2015.[140] T. Ohzuku, “Zero-Strain InsertionMaterial of Li[Li13Ti53O4] for Rechargeable LithiumCells,” Journal of The Electrochemical Society, vol. 142, no. 5, p. 1431, 1995.[141] E. Ferg, R. J. Gummow, A. de Kock, M. M. Thackeray, A. de Kock, and M. M.Thackeray, “Spinel Anodes for Lithium-Ion Batteries,” Journal of the ElectrochemicalSociety, vol. 141, no. 11, pp. L147—-L150, 1994.175Bibliography[142] L. Zhang, M. Zhang, Y. Wang, Z. Zhang, G. Kan, C. Wang, Z. Zhong, and F. Su,“Graphitized porous carbon microspheres assembled with carbon black nanoparticlesas improved anode materials in Li-ion batteries,” Journal of Materials Chemistry A,vol. 2, pp. 10161–10168, jun 2014.[143] T. F. Yi, S. Y. Yang, and Y. Xie, “Recent advances of Li4Ti5O12 as a promising nextgeneration anode material for high power lithium-ion batteries,” Journal of MaterialsChemistry A, vol. 3, pp. 5750–5777, mar 2015.[144] B. Vikram Babu, K. Vijaya Babu, G. Tewodros Aregai, L. Seeta Devi, B. Madhavi Latha,M. Sushma Reddi, K. Samatha, and V. Veeraiah, “Structural and electrical properties ofLi4Ti5O12 anode material for lithium-ion batteries,” Results in Physics, vol. 9, pp. 284–289, jun 2018.[145] N. Zhu, W. Liu, M. Xue, Z. Xie, D. Zhao, M. Zhang, J. Chen, and T. Cao, “Graphene as aconductive additive to enhance the high-rate capabilities of electrospun Li4Ti5O12 forlithium-ion batteries,” Electrochimica Acta, vol. 55, pp. 5813–5818, aug 2010.[146] M. E. Spahr, D. Goers, A. Leone, S. Stallone, and E. Grivei, “Development of carbonconductive additives for advanced lithium ion batteries,” Journal of Power Sources,vol. 196, pp. 3404–3413, apr 2011.[147] N. Kwon, D. Mouck-Makanda, and K. Fromm, “A Review: Carbon Additives inLiMnPO4- and LiCoO2-Based Cathode Composites for Lithium Ion Batteries,” Batteries,vol. 4, p. 50, oct 2018.[148] B. J. Landi, M. J. Ganter, C. D. Cress, R. A. DiLeo, and R. P. Raffaelle, “Carbon nanotubesfor lithium ion batteries,” Energy and Environmental Science, vol. 2, pp. 638–654, jun2009.[149] J. Huang and Z. Jiang, “The preparation and characterization of Li4Ti5O12/carbonnano-tubes for lithium ion battery,” Electrochimica Acta, vol. 53, pp. 7756–7759, 2008.176Bibliography[150] C. Juarez-Yescas, G. Ramos-Sánchez, and I. González, “Influence of reduced grapheneoxides (rGO) at different reduction stages as conductive additive in Li-ion batteries,”Journal of Solid State Electrochemistry, vol. 22, pp. 3225–3233, oct 2018.[151] Kunio Nishimura, Akinori Sudo, Mahito Murakami, and Koro Shirane, “Carbon fibermaterial and electrode materials for batteries,” apr 2003.[152] Y. Shi, L. Wen, S. Pei, M. Wu, and F. Li, “Choice for graphene as conductive additive forcathode of lithium-ion batteries,” Journal of Energy Chemistry, vol. 30, pp. 19–26, mar2019.[153] J. D. Martínez, N. Cardona-Uribe, R. Murillo, T. García, and J. M. López, “Carbon blackrecovery from waste tire pyrolysis by demineralization: Production and application inrubber compounding,” Waste Management, vol. 85, pp. 574–584, feb 2019.[154] J. Jiang, J. Zhu, W. Ai, Z. Fan, X. Shen, C. Zou, J. Liu, H. Zhang, and T. Yu, “Evolution ofdisposable bamboo chopsticks into uniform carbon fibers: A smart strategy to fabricatesustainable anodes for Li-ion batteries,” Energy and Environmental Science, vol. 7, no. 8,pp. 2670–2679, 2014.[155] Y. Ma, B. Ding, G. Ji, and J. Y. Lee, “Carbon-Encapsulated F-Doped Li 4 Ti 5 O 12 as aHigh Rate Anode Material for Li þ Batteries,” ACS Nano, vol. 7, no. 12, pp. 10870–10878,1087.[156] B. Priyono, P. W. Winowatan, A. Z. Syahrial, and A. Subhan, “Earth and EnvironmentalScience Optimizing the performance of Li 4 Ti 5 O 12 /LTO by addition of siliconmicroparticle in half cell litium-ion battery anodeOptimizing the performance of Li 4 Ti5 O 12 /LTO by addition of siliconmi,” in IOP Conference Series: Earth and EnvironmentalScience, vol. 105, p. 12121, 2018.[157] E. Kang, Y. S. Jung, G. H. Kim, J. Chun, U. Wiesner, A. C. Dillon, J. K. Kim, and J. Lee,“Highly Improved Rate Capability for a Lithium-Ion Battery Nano-Li4Ti5O12 Negative177BibliographyElectrode via Carbon-Coated Mesoporous Uniform Pores with a Simple Self-AssemblyMethod,” Advanced Functional Materials, vol. 21, pp. 4349–4357, nov 2011.[158] A. Jorio, E. H. Ferreira, M. V. Moutinho, F. Stavale, C. A. Achete, and R. B. Capaz,“Measuring disorder in graphene with the G and D bands,” physica status solidi (b),vol. 247, pp. 2980–2982, dec 2010.[159] T. Jawhari, A. Roid, and J. Casado, “Characterization of some commercially availablecarbon black materials,” Carbon, vol. 33, no. 11, pp. 1561–1565, 1995.[160] ASTM D 7582-15, “Standard Test Methods for Proximate Analysis of Coal and Coke byMacro Thermogravimetric Analysis,” ASTM International, 2015.[161] G. T.-K. Fey and C.-L. Chen, “High-capacity carbons for lithium-ion batteries preparedfrom rice husk,” Journal of Power Sources, vol. 97-98, pp. 47–51, jul 2001.[162] C. Troca-Torrado, M. Alexandre-Franco, C. Fernández-González, M. Alfaro-Domínguez, and V. Gómez-Serrano, “Development of adsorbents from used tirerubber: Their use in the adsorption of organic and inorganic solutes in aqueoussolution,” in Fuel Processing Technology, vol. 92, pp. 206–212, Elsevier, feb 2011.[163] D. R. Lide, G. Baysinger, L. I. Berger, R. N. Goldberg, H. V. Kehiaian, K. Kuchitsu, D. L.Roth, and D. Zwillinger, CRC handbook of chemistry and physics: a ready-reference bookof chemical and physical data. CRC Press, 2005.[164] A. Chaala, H. Darmstadt, and C. Roy, “Acid-base method for the demineralization ofpyrolytic carbon black,” Fuel Processing Technology, vol. 46, no. 1, p. 15, 1996.[165] S. Mukherjee, “Demineralization and Desulfurization of High-Sulfur Assam Coal withAlkali Treatment,” Energy & Fuels, vol. 17, pp. 559–564, 2003.[166] S. Mukherjee and P. C. Borthakur, “Effect of leaching high sulphur subbituminous coal178Bibliographyby potassium hydroxide and acid on removal of mineral matter and sulphur,” Fuel,vol. 82, pp. 783–788, may 2003.[167] X. Zhang, H. Li, Q. Cao, L. Jin, and F. Wang, “Upgrading pyrolytic residue from wastetires to commercial carbon black,”Waste Management & Research, vol. 36, pp. 436–444,may 2018.[168] Z. Song, Y. Yang, J. Sun, X. Zhao, W. Wang, Y. Mao, and C. Ma, “Effect of power levelon the microwave pyrolysis of tire powder,” Energy, vol. 127, pp. 571–580, 2017.[169] D. Hungwe, L. Ding, R. Khoshbouy, K. Yoshikawa, and F. Takahashi, “Kinetics andPhysicochemical Morphology Evolution of Low and High-Ash Pyrolytic Tire Charduring CO2 Gasification,” Energy and Fuels, vol. 34, pp. 118–129, jan 2020.[170] G. Ting-Kuo Fey, K.-L. Chen, and Y.-C. Chang, “Effects of surface modification onthe electrochemical performance of pyrolyzed sugar carbons as anode materials forlithium-ion batteries,” Materials Chemistry and Physics, vol. 76, no. 1, pp. 1–6, 2002.[171] I. Elizabeth, B. P. Singh, S. Trikha, and S. Gopukumar, “Bio-derived hierarchicallymacro-meso-micro porous carbon anode for lithium/sodium ion batteries,” Journal ofPower Sources, vol. 329, pp. 412–421, 2016.[172] S. Singh, C. Wu, and P. T. Williams, “Pyrolysis of waste materials using TGA-MS andTGA-FTIR as complementary characterisation techniques,” Journal of Analytical andApplied Pyrolysis, vol. 94, pp. 99–107, 2012.[173] M. Boota, M. P. Paranthaman, A. K. Naskar, Y. Li, K. Akato, and Y. Gogotsi, “Waste TireDerived Carbon-Polymer Composite Paper as Pseudocapacitive Electrode with LongCycle Life,” ChemSusChem, vol. 8, pp. 3576–3581, nov 2015.[174] V. Ţucureanu, A. Matei, and A. M. Avram, “FTIR Spectroscopy for Carbon FamilyStudy,” Critical Reviews in Analytical Chemistry, vol. 46, pp. 502–520, nov 2016.179Bibliography[175] Z. Loloie, M. Mozaffarian, M. Soleimani, and N. Asassian, “Carbonization and CO2activation of scrap tires: Optimization of specific surface area by the Taguchi method,”Korean Journal of Chemical Engineering, vol. 34, pp. 366–375, feb 2017.[176] M. Hofman and R. Pietrzak, “Adsorbents obtained from waste tires for NO2 removalunder dry conditions at room temperature,” Chemical Engineering Journal, vol. 170,pp. 202–208, may 2011.[177] J. M. V. Nabais, C. Laginhas, P. J. M. Carrott, M. M. L. Ribeiro Carrott, C. Galacho,J. E. C. Amorós, and A. V. N. Gisbert, “Characterization of the Surface of ActivatedCarbons Produced from Tire Residues,”Materials science forum, vol. 636-637, pp. 1383–1388, 2010.[178] R. Murillo, M. Navarro, J. López, T. Garcıéa, M. Callén, E. Aylón, and A. Mastral,“Activation of pyrolytic tire char with CO2: kinetic study,” Journal of Analytical andApplied Pyrolysis, vol. 71, pp. 945–957, jun 2004.[179] J. Zhang, I. Jones, M. Zhu, Z. Zhang, J. Preciado-Hernandez, and D. Zhang, “PoreDevelopment During CO2 and Steam Activation of a Spent Tyre Pyrolysis Char,”Wasteand Biomass Valorization, vol. 1, p. 3, jul 2020.[180] M. Betancur, J. D. Martínez, R. Murillo, J. Daniel Martínez, and R. Murillo, “Productionof activated carbon by waste tire thermochemical degradation with CO2,” Journal ofHazardous Materials, vol. 168, pp. 882–887, sep 2009.[181] S. K. S. W., Sing; D.H., Everett; R.A.W., Haul; L., Moscou; R.A., Pierotti; J., Rouquerol;T., “Reporting physisorption data for gas/solid systems with special reference to thedetermination of surface area and porosity,” Pure and applied chemistry, vol. 57, no. 4,p. 603, 1985.[182] Y. Zhang, Y. Zheng, M. Yang, and Y. Song, “Effect of fuel origin on synergy during co-180Bibliographygasification of biomass and coal in CO2,” Bioresource Technology, vol. 200, pp. 789–794,jan 2016.[183] K. Xu, Y. Li, J. Xiong, X. Ou, W. Su, G. Zhong, and C. Yang, “Activated AmorphousCarbon With High-Porosity Derived From Camellia Pollen Grains as Anode Materialsfor Lithium/Sodium Ion Batteries,” Frontiers in Chemistry, vol. 6, p. 366, sep 2018.[184] R. Jason, Role of Conductive Carbons in Lithium-ion Batteries : A SpectroscopicInvestigation. PhD thesis, Northeastern University, 2017.[185] E. L. K. Mui, D. C. K. Ko, and G. McKay, “Production of active carbons from waste tyres- A review,” Carbon, vol. 42, pp. 2789–2805, jan 2004.[186] F. Xu, B. Wang, D. Yang, X. Ming, Y. Jiang, J. Hao, Y. Qiao, and Y. Tian, “TG-FTIR andPy-GC/MS study on pyrolysis mechanism and products distribution of waste bicycletire,” Energy Conversion and Management, vol. 175, pp. 288–297, nov 2018.[187] E. Irisarri, A. Ponrouch, and M. R. Palacin, “Review—Hard Carbon Negative ElectrodeMaterials for Sodium-Ion Batteries,” Journal of The Electrochemical Society, vol. 162,pp. A2476—-A2482, jan 2015.[188] K. A. See, M. A. Lumley, G. D. Stucky, C. P. Grey, and R. Seshadri, “Reversible Capacityof Conductive Carbon Additives at Low Potentials: Caveats for Testing AlternativeAnode Materials for Li-Ion Batteries,” Journal of The Electrochemical Society, vol. 164,p. A327, dec 2016.[189] B. Peng, Y. Xu, X. Wang, X. Shi, and F. M. Mulder, “The electrochemical performance ofsuper P carbon black in reversible Li/Na ion uptake,” Science China Physics, Mechanics& Astronomy 2017 60:6, vol. 60, pp. 1–8, apr 2017.[190] J. Ou, Y. Zhang, L. Chen, Q. Zhao, Y. Meng, Y. Guo, and D. Xiao, “Nitrogen-rich porous181Bibliographycarbon derived from biomass as a high performance anode material for lithium ionbatteries,” Journal of Materials Chemistry A, vol. 3, pp. 6534–6541, mar 2015.[191] J. Wang, P. Nie, B. Ding, S. Dong, X. Hao, H. Dou, and X. Zhang, “Biomass derivedcarbon for energy storage devices,” feb 2017.[192] M. Shi, Y. Chen, H. Wen, and Y. Liu, “One-step heat treatment to process semi-cokepowders as an anode material with superior rate performance for Li-ion batteries,” RSCAdvances, vol. 8, no. 72, pp. 41207–41217, 2018.[193] S. Agarkar, P. Yadav, R. Fernandes, D. Kothari, A. Suryawanshi, and S. Ogale, “Minute-made activated porous carbon from agro-waste for Li-ion battery anode using a lowpower microwave oven,” Electrochimica Acta, vol. 212, pp. 535–544, 2016.[194] J. Gao, C. Jiang, and C.Wan, “Influence of carbon additive on the properties of sphericalLi4Ti5O12 and LiFePO4 materials for lithium-ion batteries,” Ionics 2010 16:5, vol. 16,pp. 417–424, feb 2010.[195] B. L. Ellis and L. F. Nazar, “Sodium and sodium-ion energy storage batteries,” CurrentOpinion in Solid State and Materials Science, vol. 16, pp. 168–177, aug 2012.[196] L. Chen, Y. Zhang, C. Lin, W. Yang, Y. Meng, Y. Guo, M. Li, and D. Xiao, “Hierarchicallyporous nitrogen-rich carbon derived from wheat straw as an ultrahigh-rate anode forlithium ion battery,” Journal of Materials Chemistry A, vol. 2, no. 25, pp. 9684–9690,2014.[197] C. Jin, W. Zhang, Z. Zhuang, J. Wang, H. Huang, Y. Gan, Y. Xia, C. Liang, J. Zhang, andX. Tao, “Enhanced sulfide chemisorption using boron and oxygen dually doped multi-walled carbon nanotubes for advanced lithium–sulfur batteries,” Journal of MaterialsChemistry A, vol. 5, pp. 632–640, jan 2017.182Bibliography[198] P. Bruce, S. Freunberger, and L. Hardwick, “Li–O2 and Li–S batteries with high energystorage ,” Nature materials, vol. 11, no. 1, pp. 19–29, 2012.[199] V. Vélez, B. López, R. Palacio, and L. Sierra, “A Novel Mesoporous Carbon as PotentialConductive Additive for a Li-Ion Battery Cathode,” C 2019, Vol. 5, Page 81, vol. 5, p. 81,dec 2019.[200] Y. Liu, Y. Zhu, and Y. Cui, “Challenges and opportunities towards fast-charging batterymaterials,” Nature Energy 2019 4:7, vol. 4, pp. 540–550, jun 2019.[201] Z. Zhou, H. Zhang, Y. Zhou, H. Qiao, A. Gurung, R. Naderi, H. Elbohy, A. L. Smirnova,H. Lu, S. Chen, and Q. Qiao, “Binder Free Hierarchical Mesoporous Carbon Foam forHigh Performance Lithium Ion Battery,” Scientific Reports, vol. 7, dec 2017.[202] C.-Y. Tang and S. J. Dillon, “In Situ Scanning Electron Microscopy Characterization oftheMechanism for Li Dendrite Growth,” Journal of The Electrochemical Society, vol. 163,2016.[203] A. Friesen, F. Horsthemke, X. Mönnighoff, G. Brunklaus, R. Krafft, M. Börner,T. Risthaus, M. Winter, and F. M. Schappacher, “Impact of cycling at low temperatureson the safety behavior of 18650-type lithium ion cells: Combined study of mechanicaland thermal abuse testing accompanied by post-mortem analysis,” Journal of PowerSources, vol. 334, pp. 1–11, dec 2016.[204] E. Buiel and J. R. Dahn, “Li-insertion in hard carbon anodematerials for Li-ion batteries,”Electrochimica Acta, vol. 45, pp. 121–130, sep 1999.[205] Y.-S. Hu, P. Adelhelm, B. M. Smarsly, S. Hore, M. Antonietti, and J. Maier, “Synthesisof Hierarchically Porous Carbon Monoliths with Highly Ordered Microstructure andTheir Application in Rechargeable Lithium Batteries with High-Rate Capability,”Advanced Functional Materials, vol. 17, pp. 1873–1878, aug 2007.183Bibliography[206] B. J. Campbell, Development of High Performance, Next-Generation Li-ion BatteryElectrode Materials: Sulfur, Carbon and Silicon. PhD thesis, UNIVERSITY OFCALIFORNIA RIVERSIDE, 2016.[207] J. Hou, C. Cao, F. Idrees, and X. Ma, “Hierarchical Porous Nitrogen-DopedCarbon Nanosheets Derived from Silk for Ultrahigh-Capacity Battery Anodes andSupercapacitors,” ACS Nano, vol. 9, pp. 2556–2564, mar 2015.[208] J. Niu, R. Shao, J. Liang, M. Dou, Z. Li, Y. Huang, and F. Wang, “Biomass-derived mesopore-dominant porous carbons with large specific surface area andhigh defect density as high performance electrode materials for Li-ion batteries andsupercapacitors,” Nano Energy, vol. 36, pp. 322–330, jun 2017.[209] V. Velez, G. Ramos-Sánchez, B. Lopez, L. Lartundo-Rojas, I. González, and L. Sierra,“Synthesis of novel hard mesoporous carbons and their applications as anodes for Liand Na ion batteries,” Carbon, vol. 147, pp. 214–226, jun 2019.[210] M. Ishikawa, M. Morita, M. Asao, Y. Matsuda, . Y. Sasaki, S. Goto, M. Handa, D. Kagaku,. E. Plichta, M. Salomon, S. Slane, M. Uchiyama, . M. Salomon, M. Xu, S. Petrucci,. M. Delsignore, H. Farber, . R. Zana, J. E. Desnoyers, G. Perron, R. L. Kay, andK. Lee, “Lithium Insertion in High Capacity Carbonaceous Materials,” Journal of TheElectrochemical Society J. Electrochem. Soc, vol. 142, no. 8, p. 113, 1995.[211] H. Honbo, K. Takei, Y. Ishii, and T. Nishida, “Electrochemical properties and Lideposition morphologies of surface modified graphite after grinding,” Journal of PowerSources, vol. 189, pp. 337–343, apr 2009.[212] T. Waldmann, B. I. Hogg, and M. Wohlfahrt-Mehrens, “Li plating as unwanted sidereaction in commercial Li-ion cells – A review,” Journal of Power Sources, vol. 384,pp. 107–124, apr 2018.184Bibliography[213] H. Zheng, Q. Qu, L. Zhang, G. Liu, and V. S. Battaglia, “Hard carbon: a promisinglithium-ion battery anode for high temperature applications with ionic electrolyte,”RSC Advances, vol. 2, p. 4904, may 2012.[214] X. Zhu, T. K. A Hoang, and P. Chen, “Novel Carbon Materials in the CathodeFormulation for High Rate Rechargeable Hybrid Aqueous Batteries,” Energies, vol. 10,no. 11, 2017.[215] S. Zhou, G. Liu, N. Ding, L. Shang, R. Dang, and J. Zhang, “Improved performances oflithium-ion batteries by graphite-like carbon modified current collectors,” Surface andCoatings Technology, vol. 399, p. 126150, oct 2020.[216] P. C. Goonetilleke, J. P. Zheng, and D. Roy, “Effects of Surface-Film Formation onthe Electrochemical Characteristics of LiMn2O4 Cathodes of Lithium Ion Batteries,”Journal of The Electrochemical Society, vol. 156, p. A709, jun 2009.[217] X. M. Liu, Z. dong Huang, S. woon Oh, B. Zhang, P. C. Ma, M. M. Yuen, and J. K. Kim,“Carbon nanotube (CNT)-based composites as electrode material for rechargeable Li-ion batteries: A review,” jan 2012.[218] L. Fransson, T. Eriksson, K. Edström, T. Gustafsson, and J. O. Thomas, “Influence ofcarbon black and binder on Li-ion batteries,” Journal of Power Sources, vol. 101, pp. 1–9,oct 2001.[219] K. Takei, N. Terada, K. Kumai, T. Iwahori, T. Uwai, and T. Miura, “Effects of themacroscopic structure of carbon black on its behaviour as the anode in a lithiumsecondary cell,” Journal of Power Sources, vol. 55, pp. 191–195, jun 1995.[220] W. Kwon, J. M. Kim, and S. W. Rhee, “A new equivalent circuit model for porous carbonelectrodes in charge transfer reaction of iodide/triiodide redox couples,” ElectrochimicaActa, vol. 68, pp. 110–113, apr 2012.185[221] A. K. Sleigh and U. von Sacken, “Unusual cycling behaviour of disordered carbons inLi/C cells,” Solid State Ionics, vol. 57, pp. 99–102, sep 1992.[222] Y. Liu, X. Li, L. Fan, S. Li, H. Maleki Kheimeh Sari, and J. Qin, “A Review of Carbon-Based Materials for Safe Lithium Metal Anodes,” nov 2019.[223] N. A. Kaskhedikar and J. Maier, “Lithium Storage in Carbon Nanostructures,” AdvancedMaterials, vol. 21, pp. 2664–2680, jul 2009.[224] X. Qi, B. Blizanac, A. Dupasquier, M. Oljaca, J. Li, and M. Winter, “Understandingthe influence of conductive carbon additives surface area on the rate performance ofLiFePO4 cathodes for lithium ion batteries,” Carbon, vol. 64, pp. 334–340, nov 2013.[225] Z. Zhou, F. Chen, T. Kuang, L. Chang, J. Yang, P. Fan, Z. Zhao, and M. Zhong, “Lignin-derived hierarchical mesoporous carbon and NiO hybrid nanospheres with exceptionalLi-ion battery and pseudocapacitive properties,” Electrochimica Acta, vol. 274, pp. 288–297, jun 2018.[226] X. Guo, H. F. Xiang, T. P. Zhou, X. K. Ju, and Y. C. Wu, “Morphologies and structuresof carbon coated on Li4Ti5O12 and their effects on lithium storage performance,”Electrochimica Acta, vol. 130, pp. 470–476, jun 2014.[227] X. Sun, P. V. Radovanovic, and B. Cui, “Advances in spinel Li 4 Ti 5 O 12 anodematerialsfor lithium-ion batteries,” New Journal of Chemistry, vol. 39, no. 1, pp. 38–63, 2015.186Appendix A: Leaching ExperimentsFigure A.1: Repeats from SEM-EDS analysis of raw carbon char.Figure A.2: SEM-EDS analysis of different grades of rCB obtained by modification of NaOHconcentration (without normalization).187Appendix A: Leaching ExperimentsTable A.1: Effect of type of acid used for leaching on purity of rCB (at 5 M concentration, 2hours, slurry ration 50g/L) from SEM-EDS analysis without normalization.Element Raw carbonchar 5 M H2SO4 5 M HCl 5MHNO3C 63.78 ± 2.96 56.92±1.45 57.78±0.60 56.78±0.41O 8.28 ± 1.37 7.77±0.50 8.95±1.02 11.60±1.19Zn 2.96 ± 0.55 0.20±0.03 0.00±0.00 0.09±0.02S 1.76 ± 0.35 1.22±0.18 0.57±0.04 0.91±0.07Si 1.11 ± 0.23 1.89±0.15 1.02±0.11 1.64±0.07Na 0.39 ± 0.09 0.02±0.01 0.00±0.00 0.00±0.00Mg 0.17 ± 0.05 0.15±0.00 0.11±0.02 0.14±0.01Fe 0.17 ± 0.03 0.05±0.20 0.00±0.00 0.04±0.01Ca 0.11 ± 0.03 0.01±0.00 0.00±0.00 0.01±0.01K 0.06 ± 0.01 0.03±0.01 0.00±0.00 0.03±0.01Cl 0.00 ± 0.00 0.00±0.00 0.03±0.03 0.00±0.00Table A.2: Effect of type of acid used for leaching on purity of rCB (at 10 M concentration)from SEM-EDS analysis without normalization.Element Raw carbonchar 10 M H2SO4 10 M HCl 10 M HNO3C 63.78 ± 2.96 57.95±0.48 58.23±1.23 56.31±0.74O 8.28 ± 1.37 9.57±1.60 10.28±1.21 9.87±0.61Zn 2.96 ± 0.55 0.30±0.0 0.06±0.02 0.07±0.01S 1.76 ± 0.35 1.09±0.25 0.82±0.09 1.20±0.18Si 1.11 ± 0.23 1.57±0.26 1.63±0.12 1.98±0.17Na 0.39 ± 0.09 0.04±0.01 0.02±0.01 0.01±0.00Mg 0.17 ± 0.05 0.13±0.01 0.13±0.02 0.18±0.03Fe 0.17 ± 0.03 0.04±0.02 0.03±0.03 0.02±0.00Ca 0.11 ± 0.03 0.00±0.00 0.01±0.00 0.00±0.00K 0.06 ± 0.01 0.03±0.01 0.03±0.01 0.03±0.01Cl 0.00 ± 0.00 0.00±0.00 0.06±0.00 0.01±0.01188Appendix A: Leaching ExperimentsTable A.3: Effect of concentration of HCl used for leaching on purity of rCB from SEM-EDSanalysis without normalization.Element Raw carbonchar 1 M HCl 5 M HCl 10 M HClC 63.78 ± 2.96 56.85 ± 2.04 57.78 ±0.60 58.23±1.23O 8.28 ± 1.37 5.54 ±1.43 8.95±1.02 10.28±1.21Zn 2.96 ± 0.55 1.19 ±0.31 0.00±0.00 0.06±0.02S 1.76 ± 0.35 1.19±0.23 0.57±0.04 0.82±0.09Si 1.11 ± 0.23 1.17 ±0.11 1.02±0.11 1.63±0.12Na 0.39 ± 0.09 0.11±0.01 0.00±0.00 0.02±0.01Mg 0.17 ± 0.05 0.10±0.03 0.11±0.02 0.13±0.02Fe 0.17 ± 0.03 0.07±0.06 0.00±0.00 0.03±0.03Ca 0.11 ± 0.03 0.00±0.00 0.00±0.00 0.01±0.00K 0.06 ± 0.01 0.04±0.00 0.00±0.00 0.03±0.01Cl 0.00 ± 0.00 0.00±0.00 0.03±0.03 0.06±0.00Table A.4: Effect of slurry ratio used for HCl leaching on purity of rCB from SEM-EDSanalysis without normalization (at 1M HCl for 24 hours).Element Raw carbonchar 10 20 50 80C 63.78±2.96 68.51±0.60 63.11±3.47 64.80±1.48 60.10±3.34O 8.28±1.37 6.61±1.41 5.42±1.04 5.17±0.81 5.07±0.48Zn 2.96± 0.55 0.06±0.11 0.21±0.05 0.27±0.02 0.33±0.13S 1.76± 0.35 0.95±0.16 1.00±0.18 1.20±0.20 1.20±0.19Si 1.11± 0.23 1.62±0.16 1.44±0.10 1.57±0.10 1.46±0.16Na 0.39± 0.09 0.00±0.00 0.00±0.00 0.00±0.00 0.00±0.00Mg 0.17± 0.05 0.11±0.02 0.12±0.03 012±0.02 0.11±0.02Fe 0.17± 0.03 0.00±0.00 0.05±0.04 0.05±0.08 0.04±0.06Ca 0.11±0.03 0.00±0.00 0.00±0.00 0.00±0.00 0.00±0.00K 0.06±0.01 0.02±0.03 0.01±0.02 0.00±0.00 0.00±0.00Cl 0.00±0.00 0.02±0.04 0.04±0.00 0.00±0.00 0.00±0.00189Appendix A: Leaching ExperimentsTable A.5: Effect of HCl leaching time on purity of rCB obtained from SEM-EDS analysiswithout normalization.ElementRawcarbonchar2 6 12 18 24C 63.78±2.96 56.85±2.04 57.78±0.60 65.04±2.12 67.69±2.56 60.86±1.04O 8.28 ± 1.37 5.54 ±1.43 8.95±1.02 8.26±2.12 7.69±1.11 8.81±2.24Zn 2.96 ± 0.55 1.19 ±0.31 0.00±0.00 0.00±0.00 0.00±0.00 0.00±0.00S 1.76 ± 0.35 1.19±0.23 0.57±0.04 0.59±0.26 0.78±0.19 0.59±0.11Si 1.11 ± 0.23 1.17 ±0.11 1.02±0.11 1.20±0.36 1.42±0.23 1.13±0.17Na 0.39 ± 0.09 0.11±0.01 0.00±0.00 0.00±0.00 0.00±0.00 0.00±0.00Mg 0.17 ± 0.05 0.10±0.03 0.11±0.02 0.10±0.03 0.12±0.03 0.07±0.02Fe 0.17 ± 0.03 0.07±0.06 0.00±0.00 0.00±0.00 0.03±0.06 0.00±0.00Ca 0.11 ± 0.03 0.00±0.00 0.00±0.00 0.00±0.00 0.00±0.00 0.00±0.00K 0.06 ± 0.01 0.04±0.00 0.00±0.00 0.00±0.00 0.00±0.00 0.00±0.00Cl 0.00 ± 0.00 0.00±0.00 0.03±0.03 0.06±0.02 0.02±0.03 0.00±0.00Table A.6: Effect of type of base used for leaching on purity of rCB from SEM-EDS analysiswithout normalization.Element Raw carbonchar 5 M NaOH 5 M KOH10 MNaOH 10 M KOHC 63.78 ± 2.96 56.85 ± 2.04 57.78 ±0.60 66.16±1.17 58.25±0.27O 8.28 ± 1.37 5.54 ±1.43 8.95±1.02 4.86±0.87 8.48±0.30Zn 2.96 ± 0.55 1.19 ±0.31 0.00±0.00 0.36±3.23 1.90±0.01S 1.76 ± 0.35 1.19±0.23 0.57±0.04 1.86±0.20 1.25±0.03Si 1.11 ± 0.23 1.17 ±0.11 1.02±0.11 0.87±0.07 0.59±0.02Na 0.39 ± 0.09 0.11±0.01 0.00±0.00 0.36±0.05 0.00±0.00Mg 0.17 ± 0.05 0.10±0.03 0.11±0.02 0.15±0.01 0.10±0.01Fe 0.17 ± 0.03 0.07±0.06 0.00±0.00 0.14±0.02 0.11±0.02Ca 0.11 ± 0.03 0.00±0.00 0.00±0.00 0.07±0.01 0.07±0.01K 0.06 ± 0.01 0.04±0.00 0.00±0.00 0.00±0.00 0.04±0.00Cl 0.00 ± 0.00 0.00±0.00 0.03±0.03 0.00±0.00 0.00±0.00190Appendix A: Leaching ExperimentsTable A.7: Effect of concentration of NaOH used for leaching on purity of rCB from SEM-EDS analysis without normalization.Element Raw carbonchar 1 M NaOH 5 M NaOH 10 M NaOHC 63.78 ± 2.96 56.85 ± 2.04 57.78 ±0.60 66.16±1.17O 8.28 ± 1.37 5.54 ±1.43 8.95±1.02 4.86±0.87Zn 2.96 ± 0.55 3.85 ±0.77 3.85±0.25 3.23±0.43S 1.76 ± 0.35 2.27±0.41 2.21±0.11 1.86±0.20Si 1.11 ± 0.23 1.17 ±0.11 1.03±0.06 0.87±0.07Na 0.39 ± 0.09 0.11±0.01 0.00±0.00 0.36±0.05Mg 0.17 ± 0.05 0.10±0.03 0.11±0.02 0.15±0.01Fe 0.17 ± 0.03 0.07±0.06 0.00±0.00 0.14±0.02Ca 0.11 ± 0.03 0.00±0.00 0.00±0.00 0.07±0.01K 0.06 ± 0.01 0.04±0.00 0.00±0.00 0.00±0.00Cl 0.00 ± 0.00 0.00±0.00 0.03±0.03 0.00±0.00Table A.8: Effect of slurry ratio used for NaOH leaching on purity of rCB from SEM-EDSanalysis without normalization (1M NaOH for 24 hrs).Element Raw carbonchar 10 20 50 80C 63.78 ± 2.96 56.85 ± 2.04 57.78 ±0.60 58.54±0.34 59.12±0.26O 8.28 ± 1.37 5.54 ±1.43 8.95±1.02 6.47±1.81 6.13±0.75Zn 2.96 ± 0.55 1.19 ±0.31 0.00±0.00 3.85±0.77 4.27±0.54S 1.76 ± 0.35 1.19±0.23 0.57±0.04 2.27±0.41 2.42±0.22Si 1.11 ± 0.23 1.17 ±0.11 1.02±0.11 1.31±0.17 1.35±0.04Na 0.39 ± 0.09 0.11±0.01 0.00±0.00 0.42±0.01 0.44±0.05Mg 0.17 ± 0.05 0.10±0.03 0.11±0.02 0.14±0.02 0.15±0.02Fe 0.17 ± 0.03 0.07±0.06 0.00±0.00 0.10±0.07 0.16±0.02Ca 0.11 ± 0.03 0.00±0.00 0.00±0.00 0.08±0.06 0.15±0.01K 0.06 ± 0.01 0.04±0.00 0.00±0.00 0.01±0.02 0.03±0.03Cl 0.00 ± 0.00 0.00±0.00 0.03±0.03 0.00±0.00 0.00±0.00191Appendix A: Leaching ExperimentsTable A.9: Effect of NaOH leaching time on purity of rCB from SEM-EDS analysis withoutnormalization.ElementRawcarbonchar2 6 12 18 24C 63.78±2.96 56.85±2.04 57.78±0.60 59.22±0.59 60.12±0.22 61.22±3.75O 8.28 ± 1.37 5.54 ±1.43 8.95±1.02 8.28±0.55 5.54±0.36 5.95±0.78Zn 2.96 ± 0.55 2.98 ±2.51 4.26 ±0.51 4.93±0.69 3.70±0.28 3.85±0.25S 1.76 ± 0.35 1.83±0.37 1.04±0.04 2.03±0.16 2.26±0.15 2.21±0.11Si 1.11 ± 0.23 1.17 ±0.11 1.02±0.11 1.12±0.08 1.13±0.05 1.03±0.06Na 0.39 ± 0.09 0.11±0.01 0.00±0.00 1.40±0.08 0.37±0.02 0.32±0.05Mg 0.17 ± 0.05 0.10±0.03 0.11±0.02 0.14±0.03 0.18±0.04 0.18±0.00Fe 0.17 ± 0.03 0.07±0.06 0.00±0.00 0.16±0.02 0.15±0.03 0.07±0.07Ca 0.11 ± 0.03 0.00±0.00 0.00±0.00 0.15±0.01 0.13±0.02 0.07±0.02K 0.06 ± 0.01 0.04±0.00 0.00±0.00 0.05±0.04 0.01±0.03 0.01±0.02Cl 0.00 ± 0.00 0.00±0.00 0.03±0.03 0.00±0.00 0.00±0.00 0.00±0.00Table A.10: Repeated TGA proximate analysis results of base treatment on raw carbon char.Sample Ash (%) Volatiles (%) Moisture (%) FC (%)10 M HCl 5.27 4.98 0.96 88.795 M HNO3 5.36 5.83 1.09 87.725 M KOH 9.65 5.64 0.74 83.9710 M H2SO4 5.05 4.74 0.96 89.255 M HCl 5.19 4.58 0.80 89.4210 M H2SO4 5.45 5.22 1.15 88.1810 M HNO3 4.98 7.08 1.56 86.38Leached CB 1.63 6.94 1.01 90.42Table A.11: Elemental analysis results of leached carbon black.Sample Carbon(wt%)Hydrogen(wt%)Nitrogen(wt%)Sulphur(wt%)Oxygen(wt%)Ash(wt%)Raw carbon char 80.10 0.91 0.38 3.51 4.82 10.28Leached CB 93.00 1.40 - 0.94 4.34 0.32192Appendix A: Leaching Experimentsa bc ddFigure A.3: TEM-EDS mapping results of raw CB: a) C map, b) O map, c) Si map, d) Fe map,and e) Al map.193Appendix B: Heat TreatmentExperimentsTable B.1: Burnoff values from activation of leached CB.Sample Burnoff (%)CO2AC (800-3) 6.88CO2AC (900-1) 17.21CO2AC (900-2) 42.38CO2AC (900-3) 31.64CO2AC (900-6) 30.86CO2AC (1000-3) 57.72KOHAC (700-2-4) 10.13KOHAC (800-2-4) 14.52KOHAC (900-1-4) 14.89KOHAC (900-2-1) 8.87KOHAC (900-2-2) 13.78KOHAC (900-2-4) 15.08KOHAC (900-3-4) 16.72KOHAC (900-3-4) 15.15KOHAC (900-3-4) 14.74KOHAC (900-2-5) 18.70Table B.2: Peak temperatures of three DTA peaks for different sample temperature andholding times.Sample HR Peak 1 (°C) Peak 2 (°C) Peak 3 (°C)900 °C, 1 h, 10 °C/min 222.4 580.6 900950 °C, 1 h, 10 °C/min 216.6 580 866.61000 °C, 1 h, 10 °C/min 214.9 583.3 890.51000 °C, 2 h, 10 °C/min 219.4 616.9 899.31000 °C, 3 h, 10 °C/min 213.5 631.6 883.3194Appendix B: Heat Treatment ExperimentsFigure B.1: Raman spectroscopy repeats of Super-P.Table B.3: N2 adsorption results from non-activated CB samples.Sample SBET(m2/g)Total porevolume(cm3/g)Microporevolume(cm3/g)Raw CB 62 0.13 0.0000Leached CB 68 0.15 0.0000Leached CB + heat 76 0.17 0.0008195Appendix C: ElectrochemicalExperimentsTable C.1: Electrochemical parameters of activated rCB doped LTO anodes obtained fromcurve fitting of EIS results.Sample RS (Ω) Cs (F) Rct (Ω) C (F) RSEI (Ω) W (Ω) chi sqLeachedCB 5.14 1.29 x 10-6 183.5 2.65 x 10-4 0.16±13.0% ±14.2% ±25.6% - - ±10.4%CO2AC(1000-3) 3.07 4.16 x 10-7 2.07 - - 1.53 x 10-4 0.14beforecycle ±21.8% ±121.4% ±1253.0% - - ±9.8%CO2AC(1000-3) 4.4 6.29 x 1011 0.18 2.03 x10124.94 x1010 4.79 x 10-4 0.08aftercycle ±11.8% ±4.35% ±5.07% ±1.40% ±1.38% ±5.6%KOHAC(900-2-4) 9.26 1.93 x 10-6 602.5 - - 5.48 x 10-3 0.13±10.3% ±11.3% ±9.4 - - ±31.8%Figure C.1: TGA analysis of all rCB samples under N2 atmosphere.196Appendix C: Electrochemical Experimentsa bc dFigure C.2: Structure of virgin rCB electrodes: a) and b) Leached CB, c) and d) Leached CB +heat.197Appendix C: Electrochemical Experimentsa bc dFigure C.3: Structure of virgin rCB electrodes (continued): a) and b)KOHAC (900-2-4), c)and d) CO2AC (1000-3).198Appendix C: Electrochemical Experimentsa bc dFigure C.4: Structure of rCB electrodes after 100 cycles of charging and discharging: a) andb) Raw carbon char, c) and d) Leached CB.199Appendix C: Electrochemical Experimentsa bc dFigure C.5: Structure of rCB electrodes after 100 cycles of charging and discharging(continued): a) and b) Super-P, c) and d) CO2AC (1000-3).200Appendix C: Electrochemical Experimentsa bc dFigure C.6: Structure of virgin LTO + rCB electrodes: a) and b) Leached CB, c) and d)Leached CB + heat.201Appendix C: Electrochemical Experimentsa bc dFigure C.7: Structure of LTO + rCB electrodes after 100 cycles of charging and discharging:a) and b) LTO+ KOH AC (900-2-4), c) and d) LTO + Super-P.202Appendix C: Electrochemical ExperimentsaFigure C.8: Charging curves for first few cycles of leached CB doped LTO anode.203Appendix C: Electrochemical ExperimentsabcFigure C.9: Curve fitting for rCB doped LTO anodes using Zsimpwin software: a) Rawcarbon char, b) Leached CB, and c) Leached CB + heat.204Appendix C: Electrochemical ExperimentsabFigure C.10: Curve fitting for rCB+LTO anodes using Zsimpwin software (continued): a)KOHAC (900-2-4), and b)CO2AC (1000-3).205Appendix D: Analysis of 5MHCl and10MNaOH Treated Raw Carbon CharTEM imaging of 5M HCl and 10M NaOH treated raw carbon chara bc cFigure D.1: TEM-imaging of 5 M HCl and 10 M NaOH.206Appendix D: Analysis of 5MHCl and 10MNaOH Treated Raw Carbon CharFigure D.2: XRD analysis of 5 M HCl and 10 M NaOH treated CB.Figure D.3: FTIR analysis of 5 M HCl and 10 M NaOH treated CB.207Appendix E: EquipmentsabFigure E.1: Equipments used for experiments: a) Fumehood, and b) Tube furnace.208Appendix E: EquipmentsabFigure E.2: Electrochemical testing details from neware software: a) C anode cycling, and b)LTO anode cycling.209Appendix E: Equipmentsa bFigure E.3: EIS analysis: a) BioLogic SAS Potentiostat, b) Electrochemical conditions.a b cFigure E.4: Material characterization equipments: a) AccuPyc for skeletal density analysis,b) Bruker XRD analyzer, and c) Mettler Toledo microgram scale.210Appendix E: EquipmentsabFigure E.5: Screenshots from WiRE software for Raman Analysis: a) Extended scaninformation, and b) Laser information.211
Thesis/Dissertation
eng
Mechanical Engineering
Vancouver : University of British Columbia Library
Attribution-NonCommercial-NoDerivatives 4.0 International
Graduate
Bichler, Lukas
Upgrading of recycled carbon for energy storage applications
Text