Slurry Casted Ultrathin Li₃Zr₂Si₂PO₁₂ Electrolyte Film for Solid-State Lithium Metal Batteries

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) Li₃Zr₂Si₂PO₁₂ (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 LiFePO₄ cathode and PPLN electrolyte exhibit excellent safety as well as electrochemical performances in the wide temperature range between room temperature (RT) and 100 °C.