Metallothermic Reduction of Silica–Carbon Composites: Revealing the Relationship Between Silicon-Based Products and the Reactivity of Reductants

Suppressing the formation of SiC during the magnesiothermic reduction of SiO2–C composite is still challenging. In this paper, the formation of SiC can be tentatively controlled by tuning the reactivity of reductants that can be modulated by alloying with Si at different atomic ratios. The reduction product is SiC when using Mg as the reductant, while the C–Si composites are formed when using the reductants with relatively low reactivity (e.g., Mg–Si alloy, Ca–Si alloy). The obtained C–Si composites reduced from C–SiO2 show excellent electrochemical performance, delivering a specific discharge capacity of 925 mAh g−1 at 1 A g−1 after 200 cycles and 825 mAh g−1 at 2 A g−1 after 300 cycles. In addition, when bio-silica is used as Si resource, the C–Si composites prepared from the rice husks also exhibit excellent electrochemical performance, delivering a specific discharge capacity of 687 mAh g−1 at 2 A g−1 after 300 cycles. Overall, the revealed reactivity–composition relationship can be extended to selectively prepare carbon- or carbide-based target materials as well as to harvest both C and Si from Si-containing waste biomasses.