Mitigating Volume Expansion and Enhancing Cycling Stability of Ferrous Fluosilicate-Modified Silicon-Based Composite Anodes for Lithium-Ion Batteries

Abstract

Silicon has emerged as a prominent candidate for anodes in advanced lithium-ion batteries due to its exceptional theoretical capacity and low operational potential. Despite its advantages, silicon-based anodes face significant challenges, including substantial volume changes, formation of unstable solid-electrolyte interphase (SEI) film, and voltage hysteresis during lithium alloying/dealloying, which compromise their cycling stability. This study introduces a novel ferrous fluosilicate (FeSiF6)-modified silicon-based composite anode. FeSiF6¬ is prepared via a simple reaction between Fe-Si alloys and hydrofluoric acid (HF). Various treatment methods are employed to create modified silicon-based composites with different compositions and morphologies. This innovative composite material prevents the formation of crystalline Li15Si4 and facilitates the formation of stable SEI film, thereby markedly improving the cycling stability of silicon-based anodes. Among these, the composite material Fe-Si@F@C (consisting of Fe-Si alloy@FeSiF6@graphite) demonstrates a stable discharge capacity of 975 mAh g-1 after 200 cycles at 1 A g-1, with ~94% capacity retention, and outstanding rate performance (664.4 mAh g-1 at 4 A g-1). In comparison, the Fe-Si alloy/graphite anode without FeSiF6 shows a much lower discharge capacity of 458 mAh g-1 at 1 A g-1 after 200 cycles and 291.8 mAh g-1 at 4 A g-1. These findings underscore the critical role of using FeSiF6 to modify silicon-based anodes and enhance their cycling stability, significantly advancing their potential for commercial application in next-generation lithium-ion batteries.