Tuning phase composition of Si-O-C to improve electrochemical performance of C/SiOC composites as anodes of lithium-ion batteries

Silicon oxycarbide (SiOC)-based materials hold significant potential as anodes of lithium-ion batteries (LIBs) due to their high theoretical capacity, low volume expansion, and excellent electrochemical stability. However, they exhibit low initial Coulombic efficiency (ICE) and poor cycling stability. In this study, carbon/silicon oxycarbide (C/SiOC) composites were synthesized using a facile sol-gel method followed by ambient pressure drying and thermal treatment. The phase composition of SiOC was tuned by the oxygen content of precursors to achieve a high content of reversible phase for Li storage. Among four organosilanes including trimethylethoxysilane (TMES), 1,3,5,7-tetramethylcyclotetrasiloxane (TMCTS), methyltriethoxysilane (MTES), and tetraethoxysilane (TEOS), TMCTS leads to the highest content of SiO 3 C and SiO 2 C 2 phases owing to moderate oxygen content, which are responsible for Li storage. Hence, the C/SiOC composite with TMCTS as precursor exhibits significantly higher initial Coulombic efficiency (70.53%) than those with TMES, MTES, and TEOS as precursors (68.86%, 43.85%, and 33.11%), which this value exceeds the typical ICE range of 50–60% reported for other SiOC-based materials. It was demonstrated that a higher oxygen content of the precursor promotes the generation of Li 2 O during the lithiation process, which acts as a robust structural buffer to enhanced structural stability. TMCTS-derived C/SiOC composite exhibited excellent cyclic stability over long-term cycling, retaining 601.87 mAh·g −1 after 100 cycles at 0.1 A·g −1 . The results verify the critical role of phase composition of SiOC as anodes of LIBs, providing a new strategy to design SiOC-based materials with high electrochemical performance by tuning phase composition of SiOC from its precursor.