In Situ Formation of Stable Dual-Layer Solid Electrolyte Interphase for Enhanced Stability and Cycle Life in All-Solid-State Lithium Metal Batteries.

All-solid-state lithium metal batteries have emerged as a promising solution to overcoming the energy density and safety challenges associated with conventional lithium-ion batteries. Solid polymer electrolytes, particularly those based on poly(vinylidene fluoride) (PVDF) and dimethylformamide (DMF), demonstrate significant potential. However, interfacial side reactions between residual DMF solvents and lithium metal present substantial challenges. In this study, we investigate the in situ formation of solid electrolyte interphase protective layers to mitigate these side reactions. By incorporating F-rich additives, such as fluoroethylene carbonate and lithium difluorophosphate, we successfully establish a dual-layer inorganic SEI structure characterized by an outer LiF layer and an inner LiO layer. Consequently, our approach extends the cycle life of lithium symmetric batteries to 3000 h. Additionally, the Li||LiFePO solid-state battery demonstrates exceptional stability, enduring 400 cycles at a 1C rate with an impressive capacity retention of 84%. This strategic methodology effectively leverages the benefits of residual solvents, ensuring both enhanced battery efficiency and long-term operational stability for PVDF-based all-solid-state lithium metal batteries.