Synthesis of Silicon Oxycarbide Beads from Alkoxysilane as Anode Materials for Lithium-Ion Batteries

Silicon is an important anode material for lithium-ion batteries because of its high theoretical capacity. However, the large volume expansion of silicon anodes hinders its commercial utilization. As an alternative, silicon oxycarbides (SiOCs) mitigate the expansion of anodes during lithiation, and the synthesis of SiOC beads from silanes is rather simple and at a low cost. In this study, we compared three different reactor setups for making the SiOC beads from methyltrimethoxysilane (MTMS) and found that the control of residence time was crucial. Thereby, the batch reactor turned out to be the easiest one for making monodispersed beads. We also reduced the O/Si ratio of the SiOC beads by adding dimethyldimethoxysilane (DMDMS) for better battery performance. The first-cycle delithiation capacity of the most stable material was over 1796 mA h/g, with an initial Coulombic efficiency of 82%, while the capacity retention after 170 cycles was 67% (992 mA h/g) at a charging rate of 2 A/g in the potential range of 0.01–3 V. This was among the best of the reported data so far for the SiOC beads from MTMS.