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 Li6PS5Cl0.5Br0.5 (2.0 mS cm–1). LiNi0.6Co0.2Mn0.2O2/graphite ASLBs using 40 μm thick Li6PS5Cl0.5Br0.5-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–Li6PS5Cl0.5Br0.5/Li4Ti5O12 ASLBs.

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Owing to their high Li + conductivities, mechanical sinterability, and solution processability, sulfide Li argyrodites have attracted much attention as enablers in the development of highperformance all-solid-state batteries with practicability. However, solution-processable Li argyrodites have been developed only for a composition of Li 6 PS 5 X (X = Cl, Br, I) with insufficiently high Li + conductivities (∼10 −4 S cm −1 ). Herein, we report the highest Li + conductivity of 0.54 mS cm −1 at 30 °C (Li 6.5 P 0.5 Ge 0.5 S 5 I) for solution-processable iodine-based Li argyrodites. A comparative investigation of three iodine-based argyrodites of unsubstituted and Ge-and Sn-substituted solution-processed Li 6 PS 5 I with varied heat-treatment temperature elucidates the effect of microstructural evolution on Li + conductivity. Notably, local nanostructures consisting of argyrodite nanocrystallites in solution-processed Li 6.5 P 0.5 Ge 0.5 S 5 I have been directly captured by cryogenic transmission electron microscopy, which is a first for sulfide solid electrolyte materials. Specifically, the promising electrochemical performances of all-solid-state batteries at 30 °C employing LiCoO 2 electrodes tailored by the infiltration of Li 6.5 P 0.5 Ge 0.5 S 5 I−ethanol solutions are successfully demonstrated.