Engineering Electrolytic Silicon–Carbon Composites by Tuning the In Situ Magnesium Oxide Space Holder: Molten-Salt Electrolysis of Carbon-Encapsulated Magnesium Silicates for Preparing Lithium-Ion Battery Anodes

Abstract

Fabricating hollow space between a Si core and C shell has been recognized as an efficient strategy for tailoring lithium-storage performances of the silicon–carbon composite anode by resolving the extreme volume expansion of Si. Here, we report a molten-salt electrolysis method for electroreducing carbon-encapsulated magnesium silicate to prepare a Si@void@C composite in MgCl₂-containing molten salt. The void space between carbon and silicon comes from the transition from silicate to Si as well as the removal of the in situ generated MgO, and the SiC is suppressed by tailoring the electrode potentials in MgCl₂-containing molten salt. In other words, MgO serves as an inert space holder that can be removed by an acid leaching process to create void space. The obtained Si@void@C composite delivers a specific discharge capacity of 900 mAh/g at 1 A/g, even after 300 cycles with a discharge capacity retention rate of 75.5%. Therefore, this study paves an electrochemical pathway to prepare Si@void@C composite anodes using inexpensive feedstocks, and the void space can be tuned by adjusting the amount of MgO space holder.