LiF-rich solid electrolyte interface induced by fluorinated carbon enables stable silicon anodes with high initial coulombic efficiency

Silicon (Si) is emerging as a highly promising anode material candidate for high energy-density lithium-ion batteries (LIBs). However, its significant volume expansion during cell cycling poses a substantial challenge. Herein, fluorinated carbon derived from a fluorine-rich polymer is employed as a functional layer to engineer the solid electrolyte interface (SEI) of Si based anode material, featuring LiF-rich components in the SEI film. The strong initial Coulombic efficiency (ICE)-semi-ionic F/C linear correlation in Si@C/F nanoparticles demonstrates the essential function of semi-ionic fluorine in high-efficiency Si anodes. Semi-ionic fluorine promotes preferential LiF nucleation during SEI formation, which simultaneously suppresses lithium-consuming side reactions to enhance ICE and stabilizes the electrode interface. The homogeneous LiF distribution creates low-barrier Li + diffusion channels, markedly boosting electrode kinetics for enhanced high-rate capability. As a result, the Si@C/F composite exhibits outstanding electrochemical performance, with an ICE value as high as 88.8 %. The Si@C/F composite also demonstrates excellent long-cycling stability and high-rate capability, maintaining a reversible capacity of 971.8 mAh g −1 even under 1 A g −1 for 500 cycles. This work reveals the regulation of C F bonds in the carbon layer to construct robust SEI layer in the Si/C composites, offering a strategy for advanced Si-based anode materials with both high ICE and stable cycling performance.