UBC Theses and Dissertations
Interface design for silicon-based anodes for lithium-ion batteries Zhu, Hongzheng
Lithium-ion batteries (LIBs) are promising energy storage systems for electric vehicles (EVs) and hybrid electric vehicles (HEVs). However, to meet the requirements for EVs and HEVs, the performance of commercially available LIBs needs to be greatly improved in energy density, cycling life, rate capability, and safety. It is well known that the LIB performance is highly dependent on the choice of electrode materials. Therefore, it is essential to develop new electrode materials as replacements for graphite anode used in commercial LIBs to achieve high-performance LIBs desirable for EV and HEV applications. Among all potential alternatives to graphite anode, Si-based materials are considered one of the most promising anodes due to their superior gravimetric capacity (4200 mAh g-1) and moderate discharge voltage. However, Si electrodes face several challenging issues, such as large volume changes, thick solid electrolyte interphase (SEI) layer, and electrode swelling. Hence, solving the above problems is crucial for enhancing the overall performance of Si anodes in LIBs for further practical applications. In this thesis, different coating materials were used to modify Si anode to achieve the above goal. Firstly, a facile and low-cost sol-gel method followed by annealing was developed to form a thin Al2O3 coating layer on the graphite/silicon composite anode. At 25 oC, the Al2O3-coated graphite/silicon (G/Si) electrode showed better cycling performance than the uncoated samples. The capacity retention could retain the initial capacity up to 76.4% after 100 cycles, while the uncoated G/Si could only reach 56.4%. Secondly, AlOxNy coating by plasma-enhanced atomic layer deposition (PEALD) was developed and applied on the Si electrode. By employing this as a surface modification, the confinement of silicon nanoparticles embedded into the electrode matrix is well achieved, while the kinetics of the charge/discharge process is enhanced due to the electrochemical properties of the AlOxNy film. The capacity retention of AlOxNy coated Si electrode was elevated to 72.3% (compared with 13.3% of bare Si electrode), and the capacity remains 1297.2 mAh g-1 at 140 cycles. Thirdly, a new hybrid organic-inorganic material, tincone, was developed by molecular layer deposition (MLD), and successfully applied the tincone as a surface coating on the Si electrode. The tincone coating showed excellent protective effects on Si anode. Tincone-coated Si electrode exhibited a discharge capacity of 2487.3 mAh g-1 with 70% of capacity retention after 110 cycles. Meanwhile, tincone film possessed good electrochemical activity for Li storage, making it a new organic-inorganic hybrid material in Li-ion batteries. In summary, this thesis developed three novel materials and processes for surface coating in LIBs, applied these coating materials to engineer electrode-electrolyte interfaces of Si-based anodes, and deepened fundamental understanding of nanoscale surface coating in addressing the problems in Si anodes. It is expected that this research could contribute to the development of a commeically-viable Si anode for higher-energy LIBs for electric vehicle applications.
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