Slurry Casted Ultrathin Li ₃ Zr ₂ Si ₂ PO ₁₂ Electrolyte Film for Solid‐State Lithium Metal Batteries

Abstract Thin and flexible solid‐state electrolyte (SSE) films with high ionic conductivity and low interfacial resistance are urgently required for lithium metal batteries (LMBs). However, it's still challenging to reduce the film thickness to <20 µm, especially for those with high ceramic contents. Herein, a facile slurry casting method is developed to prepare the ultra‐thin (14 µm) Li ₃ Zr ₂ Si ₂ PO ₁₂ (LZSP) films with ceramic content up to 91% using a composite polymer binder, polyvinylidene fluoride (PVDF), and polyethylene oxide (PEO). It shows that PEO not only enhanced the film flexibility but also makes it be easily peeled off to form a freestanding membrane, PLN. To promote the interfacial ion transport, PEO/lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) is introduced to the film surface, and the resultant tri‐layer film, PPLN, shows a satisfying room temperature ionic conductivity of 0.116 mS cm ⁻¹ , high Li ⁺ transference number of 0.79, and good compatibility with metal lithium. As a result, LMBs using LiFePO ₄ cathode and PPLN electrolyte exhibit excellent safety as well as electrochemical performances in the wide temperature range between room temperature (RT) and 100 °C.