Thin and Flexible Solid Electrolyte Membranes with Ultrahigh Thermal Stability Derived from Solution-Processable Li Argyrodites for All-Solid-State Li-Ion Batteries

Sheet-type solid electrolyte (SE) membranes are essential for practical all-solid-state Li batteries (ASLBs). To date, SE membrane development has mostly been based on polymer electrolytes with or without the aid of liquid electrolytes, which offset thermal stability (or safety). In this study, a new scalable fabrication protocol for thin (40–70 μm) and flexible single-ion conducting sulfide SE membranes with high conductance (29 mS) and excellent thermal stability (up to ∼400 °C) is reported. Electrospun polyimide (PI) nonwovens provide a favorable porous structure and ultrahigh thermal stability, thus accommodating highly conductive infiltrating solution-processable Li₆PS₅Cl_0.5Br_0.5 (2.0 mS cm^–1). LiNi_0.6Co_0.2Mn_0.2O₂/graphite ASLBs using 40 μm thick Li₆PS₅Cl_0.5Br_0.5-infiltrated PI membranes show promising performances at 30 °C (146 mA h g^–1) and excellent thermal stability (marginal degradation at 180 °C). Moreover, a new proof-of-concept fabrication protocol for ASLBs at scale that involves the injection of liquefied SEs into the electrode/PI/electrode assemblies is successfully demonstrated for LiCoO₂/PI–Li₆PS₅Cl_0.5Br_0.5/Li₄Ti₅O₁₂ ASLBs.