Directed Construction of a Synergistic Li ₃ P‐LiF Inorganic Solid Electrolyte Interphase Toward Stable Silicon Anodes

Silicon–carbon composite anodes offer exceptionally high energy density, but their practical application is severely constrained by the structural instability and continuous evolution of the solid electrolyte interphase (SEI). In this work, moving beyond conventional LiF‐enrichment strategies, we propose a directional regulation approach based on the rational construction of a dual‐phase inorganic SEI to stabilize silicon‐based anodes. Phosphorus‐active sites are introduced on the Si/C surface to electrochemically induce the in situ formation of a Li 3 P‐LiF composite SEI, where Li 3 P enables rapid Li + transport and LiF provides electronic insulation and chemical passivation. Their nanoscale integration yields a coherent interphase that effectively mitigates mechanical stress during silicon cycling. Comprehensive materials characterization combined with theoretical analysis demonstrates that the LiF‐Li 3 P dual‐phase SEI markedly enhances interfacial stability, increasing the Young's modulus to 8.9 GPa and enabling a high Li + diffusion coefficient of up to 12.88 × 10 −12 cm 2 s −1 . Benefiting from this synergistic SEI design, the Si/C anode delivers excellent electrochemical performance, achieving an initial Coulombic efficiency of 86.27% and retaining 87.53% of its capacity after 400 cycles at 2.0C. Moreover, the effectiveness of the interfacial design is further verified in Si/C@P||NCM622 full cells over 150 cycles at 1.0C. These results highlight fast ion conductor‐assisted dual‐phase SEI engineering as an effective and scalable strategy for enabling high‐performance silicon‐based lithium‐ion batteries.