Effect of Solvents on a Li10GeP2S12-Based Composite Electrolyte via Solution Method for Solid-State Battery Applications

Using a solution approach to process composite electrolytes for solid-state battery applications is a viable strategy for lowering the thickness of electrolyte layers and boosting the cell energy density. To fully utilize the super ionic conductivity of sulfides, more research about their solvent and binder compatibility is needed. Herein, the allowable solvent polarity is discovered through systematically pairing the solid electrolyte Li10GeP2S12 (LGPS) with eight types of aprotic solvents. To further consider the influence of oxygen and moisture solvation that is important to practical manufacturing scenario, we also design experiments to flow dry air and N2, or further mixed with water vapor, through these solvents to unveil their detrimental effects. Finally, a low polar solvent, dimethyl carbonate (DMC), and a previously unfavored commercial polymer, poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP), are chosen to fabricate a ∼40 μm thick LGPS-based composite electrolyte, giving 2 mS·cm–1 conductivity. It cycles between lithium/graphite composite electrodes at 0.5 mA·cm–2 for over 450 h with a capacity of 0.5 mAh·cm–2 and can withstand a 10-fold current surge.