Novel approach for controlling free-carbon domain in silicone oil-derived silicon oxycarbide (SiOC) as an anode material in secondary batteries

Silicon oxycarbide (SiOC) has been regarded as potential anode for lithium-ion secondary batteries (LIBs) due to high reversible capacities (higher than conventional graphite) and superior electrical conductivity with regard to free-carbon domain (FCD). Thus, controlling and optimizing the FCD in SiOC is essential factor in determining battery performance. In this study, the FCD controlled SiOC is successfully synthesized via a simple pyrolysis using silicone oil and phenyl group-containing additives (divinylbenzene (DVB)) as precursors. The DVB is critical for the incorporation of carbon to facilitate Si-O-C bonding as well as the formation of the FCD in SiOC. The SiOC anode materials show that there is a dependence between the FCD content and electrochemical performance. The FCD controlled SiOC exhibits remarkable electrochemical performance as compared to carbon-excess materials, such as high reversible capacity (550 mAh g⁻¹ at 200 mA g⁻¹), cycle stability (95% capacity retention after 200^th cycles at 200 mA g⁻¹) and superior rate capability (300 mAh g⁻¹ at 2000 mA g⁻¹).