Strategy to enhance the electrochemical performance of silicon oxycarbide as anodes in sodium-ion batteries

[Display omitted] •Highest capacity of SiOC in NIB was achieved using 1 M NaOTf in diglyme electrolyte.•Lower cell overpotential was observed using the diglyme electrolyte.•Ultrathin and inorganic SEI layer was the main reason for high capacity. Na+-ion storage capacity of silicon oxycarbides (SiOCs) can be enhanced by incorporating an ether-based electrolyte. Nonporous SiOC micron-sized particles in a sodium trifluoromethane sulfonate-diglyme electrolyte exhibit a more enhanced storage capacity (287 mAh g−1) in addition to a small capacity decay (0.002%) after 10,000 cycles. On applying a constant current constant voltage (CCCV) mode, the capacity increased to 322 mAh g−1, approaching its theoretically estimated value. In contrast to conventional ester-based electrolytes, using a diglyme-based ether electrolyte produced an ultrathin and inorganic-based solid electrolyte layer on the electrode surface. This reduces cell overpotential and volume expansion of the electrode. This study provides a rational strategy to design high-performance NIB cells.