As a remarkable alternative anode to commercial graphite for the next-generation high-performance lithium-ion batteries (LIBs), silicon (Si) has attracted tremendous attention due to its high specific capacity. However, the enormous volume expansions/contractions during the charge/discharge limited its practical application in LIBs greatly. To solve these issues, herein, we fabricated a low-cost FeSi intermetallic compound (FeSi 2 ) by the ball milling with photovoltaic industrial waste micron-sized Si and Fe powders as raw materials and encapsulated it by N, S, O-doped mesoporous carbon with polyvinylpyrrolidone as C, N, O precursor and (NH 4 ) 2 SO 4 as template and pore-introducing agent. Owing to the presence of FeSi 2 , abundant meso-pores for mitigating Si and FeSi 2 expansion and the N, S, O-doped mesoporous carbon for facilitating lithium-ion transport and electron conduction, one as-prepared FeSi 2 /N, S, O-doped mesoporous carbon composite anode (FeSiA 1 @C) showed a high specific capacity of 401.7 mAh g −1 even at 1.0 A g −1 after 1600 cycles. More impressively, the assembled LiFePO 4 || 20 % FeSiA 1 @C/80 % commercial graphite full cell presented a high energy density of ca. 312.0 Wh kg −1 and a capacity retention of ca. 80 % after 500 cycles, demonstrating a promising practical applicability of FeSiA 1 @C anode, and showing a new way for the high-value utilization of industrial waste micron-sized Si for LIBs.
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.
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