UBC Theses and Dissertations
Cathode development for all-solid-state lithium sulfur batteries Lopez Gonzalez, Daniela
EV production is currently dominated by lithium-ion technology; however, precious metal scarcity and price increases have pushed for alternative chemistries to be researched. Presently, the research of lithium metal-based batteries has increased having higher energy densities than traditional lithium-ion batteries (LIBs). The use of sulfur as the active cathode material has gained attention due to the high gravimetric capacity of sulfur (1672 mA h gˉ¹) and its abundance in the Earth’s crust. One of the biggest obstacles solid state lithium sulfur batteries faces, is the utilization and accessibility of sulfur during cycling. Due to sulfur’s low electrical (10ˉ³ S cmˉ¹) and ionic conductivity (10ˉ⁹ S cmˉ¹), Li+ and electron transport is limited, and over time hinders the cell’s capacity. Furthermore, a volumetric change during cycling are observed which pose concerns to the mechanical integrity of the cathode. Carbon supports as well as additives have been explored to promote transport, aid during volume changes, and maximize active material utilization during cycling. This study aimed to evaluate how the deposition method of sulfur onto reduced graphene oxide (rGO), as the carbon support, changed the electrochemical performance of the active material. The examined methods of sulfur deposition include an acetone method as solvent infiltration, sulfur-ethylene diamine (S-EDA) complex as reaction deposition, as well as dry ball milling (DBM) method as mechanical intrusion. The influence of heat treatment and sulfur content was also analyzed to gain insights towards the morphological and electrochemical changes of the cathode. The variation of sulfur deposition methods yielded different electrochemical results proving the synthesis method chosen can alter the arrangement and connection of sulfur on rGO. The incorporation of heat treatment above sulfur’s melting temperature after each synthesis method helped increase the dispersion of sulfur on rGO and minimized crystalline agglomerates. The Acetone method showed minimal losses during synthesis and had a high discharge current density of -0.150 mA cmˉ². Increasing the sulfur content deposited on rGO also showed to have a negative effect on the electrochemical performance of rGO with 40% sulfur deposited on rGO showing the highest initial discharge capacity at 1270 mAh gˉ¹.
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