Dual‐Enhanced Charge Transfer through Prelithiation Strategy in Polymer Electrolyte Enables Robust LiF‐Rich SEI for Ultralong‐Life All‐Solid‐State Batteries

Abstract Lithium fluoride (LiF)‐rich solid electrolyte interface (SEI) is critical for enabling the stable operation of polymer‐based all‐solid‐state lithium‐metal batteries (ASSLMBs). Precisely controlling the C─F dissociation chemistry in fluorine‐containing lithium salts to construct a LiF‐rich SEI is a logically viable but still challenging approach. Current strategies for constructing LiF‐rich SEI primarily focus on designing non‐metal polar groups and related structures. In contrast, approaches leveraging metal‐based electron donors to facilitate charge transfer for C─F bond cleavage and LiF formation remain largely unexplored. Herein, a dual‐enhanced charge transfer mechanism through prelithiation strategy is proposed in solid polymer electrolyte (SPE) for C─F bond cleavage. The charge transfer occurs between LiTFSI and the introduced metal sites and further enhanced by lithiation design, thereby achieving a robust LiF‐rich SEI. The achieving SPEs enable an excellent cyclability of Li|Li cell over 3800 h at 0.3 mA cm −2 . Li||LiFePO 4 ASSLMBs demonstrate a high Coulombic efficiency of ≈100% and a stability of 1200 cycles with capacity retention of 80% at 2C. The corresponding pouch cell delivers a high average areal capacity of 2.41 mAh cm −2 over 1600 h. This work offers a novel approach for constructing LiF‐rich SEI toward durable ASSLMBs.