In Situ Construction of Rich‐LiF/LiBr SEI by Ion‐Supported Porous Polymer Strategy for High Interfacial Stability All‐Solid‐State Lithium Metal Batteries

Abstract The solid electrolyte interphase (SEI) of rich lithium halides can effectively regulate the uniform deposition of lithium, suppress the formation and growth of lithium dendrites, and consequently enhance the overall electrochemical performance of batteries. In current research, the construction of multi‐component lithium halide SEI primarily relies on chemical bond breaking, which involves longer formation pathways for lithium halides and presents inherent limitations. In this study, the ionic liquid is grafted onto the porous polymer, facilitating the in‐situ formation of LiBr through the direct ionic transformation of Br − , thereby streamlining the reaction pathway. Meanwhile, the pyridine unit in the porous polymer can promote the fracture of the C─F bond in LiTFSI, forming a LiF‐rich SEI. Ultimately, the LiF/LiBr co‐growing lithium double halide SEI is constructed on lithium anode, which effectively inhibited the lithium dendrites growth. The experimental results demonstrate that the Li//PEO‐PBrILs//Li battery stably cycled for 4000 h at the current density of 0.1 mA cm −1 . The LiFePO 4 //PEO‐PBrILs//Li battery maintains a capacity retention rate of 80.2% after 800 cycles at 1 C. Even at 30 °C, the LiFePO 4 //PEO‐PBrILs//Li battery maintains a capacity retention of 94% after 200 cycles. This study presents a novel approach for constructing various lithium halides SEI.