High-conductivity free-standing Li6PS5Cl/poly(vinylidene difluoride) composite solid electrolyte membranes for lithium-ion batteries

Bulk-type all-solid-state batteries (ASSBs) using sulfide solid electrolyte are considered as a promising alternative to commercial lithium-ion batteries owing to their high energy density and safety. However, cell energy density is often comparatively low due to use of a thick solid electrolyte separator and a lithium alloy as anode. For achieving high-performance ASSBs, creating a thin free-standing electrolyte with high-conductivity and good cycling stability against lithium anode is essential. In this work, we present Li6PS5Cl/poly(vinylidene difluoride) (LPSCl/PVDF) composite electrolytes prepared by a slurry method. The influence of the PVDF content on the microstructure, morphology, ionic conductivity and activation energy of the LPSCl/PVDF electrolytes is systematically investigated. Free-standing LPSCl/PVDF membranes with a thickness of 100–120 μm and a high ionic conductivity of about 1·10−3 S cm−1 at 25 °C are obtained. After adding PVDF to the LPSCl electrolyte, the cycling stability of the LPSCl electrolyte against lithium metal improves significantly. Therefore, LPSCl/PVDF composite electrolytes are promising candidates to be used in ASSBs.