Chemical Vapor Deposition Carbon Coating of SiOx Anode for Li-Ion Batteries: Significance of Carbon Precursor Selection and Deposition Temperature

Owing to the surge in the demand for lithium-ion batteries (LIBs) with high energy density, silicon suboxide (SiOx)-based materials with impressive theoretical capacities have garnered significant attention. However, challenges such as poor electrical conductivity and substantial volume expansion must be overcome. A common strategy for addressing these issues involves coating SiOx with carbon. During this process, the properties of the carbon layer and SiOx are strongly affected by the temperature and precursor choice. This study explores the impact of the temperature and precursor selection on the carbon coating layer deposited by chemical vapor deposition (CVD) and the phase of SiOx. Surprisingly, SiOx@C2H2, in which SiOx was coated with carbon using acetylene at low temperatures, exhibited lower cyclic stability than the uncoated SiOx. In contrast, SiOx@CH4, in which SiOx was coated with carbon at high temperatures, comprised a vertically grown carbon layer and SiO2 layer with optimal thickness. This configuration stabilized the growth of the solid electrolyte interphase (SEI) layer and enhanced the electrical contact. The optimized SiOx@CH4-1000 (methane-based CVD coating at 1000 °C) demonstrated excellent electrochemical performance, achieving a high capacity of 778 mAh g–1 at 0.75 A g–1 and a remarkable capacity retention of 92.8% after 100 cycles. This optimized CVD carbon coating process paves the way for industrialization of SiOx-based materials, positioning them for application in next-generation LIBs.