Mitigating the volume expansion and enhancing the cycling stability of ferrous fluorosilicate-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 an unstable solid-electrolyte interphase (SEI) film, and voltage hysteresis during lithium alloying/dealloying, which compromise their cycling stability. This study introduces a novel ferrous fluorosilicate (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 a stable SEI film, thereby markedly improving the cycling stability of the 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 mA h g⁻¹ after 200 cycles at 1 A g⁻¹, with ∼94% capacity retention, and outstanding rate performance (664.4 mA h 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 mA h g⁻¹ at 1 A g⁻¹ after 200 cycles and 291.8 mA h g⁻¹ at 4 A g⁻¹. These findings underscore the critical role of FeSiF₆ in modifying silicon-based anodes and enhancing their cycling stability, significantly increasing their potential for commercial application in next-generation lithium-ion batteries.