Electrochemically converting micro-sized industrial Si/FeSi2 to nano Si/FeSi for the high-performance lithium-ion battery anode

Low-cost silicon (Si) feedstocks and a facile method to downsize the particle size are two determinants for the application of Si for the lithium-ion battery anode. Among various Si feedstocks, the industrial bulk ferrosilicon (b-Si/FeSi 2 ) alloy is a promising Si resource, but decreasing the particle size and increasing the utilization of Si remain challenging. Herein, we report a self-driven alloying-electrochemical dealloying approach to converting the b-Si/FeSi 2 to nano-sized Si/FeSi (n-Si/FeSi) in molten salts using Mg to extract one Si atom from one FeSi 2 molecule by breaking down the FeSi–Si chemical bond and simultaneously forming Mg 2 Si. Subsequently, the obtained FeSi and Mg 2 Si are converted to nano Si and FeSi by electrochemically removing Mg from the Mg 2 Si anode to the cathode, making a circular use of Mg and increasing the electroactive Si content. Moreover, the polydopamine-coated n-Si/FeSi (n-Si/FeSi@C) anode exhibits a high capacity of 1449.7 mAh g −1 after 500 cycles at 0.4 A g −1 , and an extremely stable reversible capacity of 846.8 mAh g −1 is retained even after 1500 cycles at 2 A g −1 . Overall, this work provides an efficient method to convert industrial bulk Si/FeSi 2 to nano-sized Si/FeSi by leveraging the chemical bonds of Fe–Si and Mg–Si.