Highly conductive and nonflammable composite polymer electrolytes for rechargeable quasi-solid-state Li-metal batteries

Solid-state Li-metal batteries are promising as next-generation energy storage devices. However, the main bottlenecks are the poor conductivity of the solid electrolyte and the high interfacial resistance. While polymers exhibit a lower interfacial resistance in comparison to ceramics, they often require the inclusion of flammable solvents. In this work, highly conductive composite polymer electrolyte (CPE) membranes are prepared by integrating a poly(vinylidene fluoride) matrix (PVDF) with a Li-conductive perovskite (i.e., Li0.38Sr0.44Ta0.70Hf0.30O2.95F0.05, LSTHF), a flame-retarding solvent (i.e., trimethyl phosphate (TMP)), and a Li salt (i.e., LiClO4). The CPE membrane with 10 wt% LSTHF (CPE-10) exhibits conductivities as high as 0.53 mS cm−1 at room temperature (RT) and 0.36 mS cm−1 at 0 °C. Furthermore, prototype batteries, including the CPE-10 electrolyte, show high initial discharge capacities, good rate capabilities, and stable cycling performance at either RT or 5 and 60 °C. This study illustrates that including a Li-conductive perovskite and TMP in a PVDF-based polymer material could yield safe, high-performance quasi-solid-state Li-metal batteries capable of operating over a relatively wide temperature range.