Annihilating the Formation of Silicon Carbide: Molten Salt Electrolysis of Carbon–Silica Composite to Prepare the Carbon–Silicon Hybrid for Lithium‐Ion Battery Anode

Silicon (Si) and carbon (C) composites hold the promise for replacing the commercial graphite anode, thus increasing the energy density of lithium‐ion batteries (LIBs). To mitigate the formation of SiC, this paper reports a molten salt electrolysis approach to prepare C‐Si composite by the electrolysis of C‐SiO2 composites. Unlike the conventional way of making a C coating on Si, C‐SiO2 composites were prepared by pyrolyzing the low‐cost sucrose and silica. The electrochemical deoxidation of the C‐SiO2 composites not only produces nanostructured Si inside the C matrix but also introduces voids between the C and Si owing to the volume shrinkage from converting SiO2 to Si. More importantly, the use of Mg ion‐containing molten salts precludes the generation of SiC, and the electrolytic Si@C composite anode delivers a capacity of about 1500 mAh g−1 after 100 cycles at a current density of 500 mA g−1. Further, the Si@C|| LiNi0.6Co0.2Mn0.2O2 full cell delivers a high energy density of 608 Wh kg−1. Overall, the molten salt approach provides a one‐step electrochemical way to convert oxides@C to metals@C functional materials.