Dual‐Ion Reconstruction of a LiF/NaF–N‐Rich Hybrid Interphase for Durable Silicon‐Carbon Anodes

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Silicon‐carbon anodes offer high capacity for lithium‐ion batteries, yet their cycling stability is limited by repeated solid‐electrolyte‐interphase (SEI) rupture during drastic volume changes. Herein, we introduce a NaNO 3 ‐DMSO additive into a conventional LiPF 6 /carbonate electrolyte to construct a durable LiF/NaF–N‐rich interphase on a porous silicon‐carbon composite (Si@pSC) through a dual‐ion cooperative mechanism. We reveal that DMSO enables NaNO 3 incorporation while preserving the carbonate‐rich Li + primary solvation sheath, with Na + strongly associating with PF 6 − and NO 3 − undergoing early interfacial reduction to seed nitrogen‐containing inorganic species. This dual‐ion synergy reconstructs the conventional carbonate‐containing SEI by incorporating LiF/NaF nanocrystalline domains and nitrate‐derived N‐containing species, thereby limiting persistent parasitic interfacial reactions while providing accelerated Li + transport pathways. Consequently, the optimized electrolyte enables Si@pSC half‐cells to deliver 365 mAh g −1 after 1000 cycles at 1 A g −1 , LFP||Si@pSC full cells retain 85.6% capacity after 1000 cycles at 2 C, and NCM811||Si@pSC full cells retain 95.4% capacity after 500 cycles at 2 C. Theoretical calculations further reveal that Na incorporation expands the fluoride lattice framework and lowers the Li + migration barrier from 0.56 to 0.42 eV. This dual‐ion interphase reconstruction strategy offers a practical pathway toward durable Si‐based anodes.