Silicon oxycarbide produced from silicone oil for high-performance anode material in sodium ion batteries

Sodium ion batteries (NIBs) have gained considerable attention for large-scale energy storage applications because of the lower cost and higher abundance of Na than Li. In this study, we demonstrate that silicon oxycarbides (SiOCs), in which free carbon phases are imbedded in amorphous glassy SiO_xC_y phases, can be promising candidates as anodes for NIBs. The SiOC samples were synthesized by the pyrolysis of low-cost silicone oil in a H₂/Ar flow condition. When tested as an anode in NIBs, the SiOC sample calcined at 900 °C exhibited an excellent reversible capacity of 160 mAh g⁻¹ at 25 mA g⁻¹ after 200 cycles and a high rate performance of 62 mAh g⁻¹ at 800 mA g⁻¹. More importantly, the SiOC electrode exhibited an excellent long-term cycling performance of 0.09 mAh g⁻¹ decay per cycle for 650 cycles. The electrochemical properties of SiOC in an NIB were compared with those in an LIB to gain an insight into its ion storage mechanism. The effects of calcination temperature, calcination time, and ball milling time on the physicochemical and electrochemical properties of the SiOC electrode are discussed.