Dual Anion‐Involved Interfacial Chemistry Enables Ultra‐Stable PEO‐Based Solid‐State Lithium Metal Batteries by Suppressing NMP‐Induced Side Reactions

The incorporation of solvent N‐methylpyrrolidone (NMP) into polyethylene oxide (PEO) weakens EO‐Li + interaction and boosts Li + transport via strong Li + affinity, but free NMP inevitably reacts with Li metal, undermining interface stability. Herein, we report a dual‐anion coordination strategy that repurposes the residual NMP from a “side‐reaction source” into a “functional component”. LiDFOB and LiNO 3 are introduced as dual‐salt additives into an NMP‐containing PEO/LiTFSI system. Leveraging the preferential coordination of DFOB– and NO 3 – with Li + , an anion‐enriched solvation sheath is constructed, which strengthens the Li + ‐NMP interactions. The modified coordination environment facilitates the preferential formation of a kinetically stable, anion‐derived solid electrolyte interphase (SEI), effectively mitigating interfacial side reactions between the NMP and Li metal. As a result, the obtained electrolyte delivers a high ionic conductivity of 1.69 × 10 −4 S cm −1 and stable cycling over 1200 h at room temperature. The assembled Li/LFP cell exhibits a high capacity retention of 93% after 2000 cycles. Even at room temperate and 0°C, the assembled Li/LFP cell maintains stable and efficient cycling. This work establishes a universal solvent structure tailoring strategy to regulate reactive solvent molecules, opening a fresh avenue for high‐performance PEO‐based solid‐state lithium metal batteries.