Constructing the lithium polymeric salt interfacial phase in composite solid-state electrolytes for enhancing cycle performance of lithium metal batteries

The solid-state lithium metal batteries are considered a promising direction for developing lithium-based energy storage devices because of their superiority over lithium-ion batteries containing liquid electrolytes in energy density and safety performance. However, the design, preparation, and optimization of solid-state electrolytes (SSEs), especially composite solid-state electrolytes (CSEs), still face critical construction design and composite process challenges. This work proposes and designs a method to construct a highly compatible and lithium-ion conductive interfacial phase by coating the inorganic phase with polymeric lithium salt in the composite solid electrolytes. The introduction of the lithium salt interfacial phase efficiently improves the cycle performance and stability of CSEs in lithium metal batteries by synergistic optimization of the composite interfacial phase. We investigate two different modification methods (solvent-free and in-situ methods) in two different inorganic systems (Li6.4La3Zr1.4Ta0.6O12 (LLZTO) and LiTa2PO8 (LTPO)) to demonstrate the practical value of this design. The highest ionic conductivity of the modified PEO/LTPO CSEs (50 wt%) can be improved to 9.3 × 10-4 S·cm−1 at 80℃ and 4.0 × 10-5 at RT (∼25℃, hereinafter inclusive), while those of the modified PEO/LLZTO CSEs can reach 1.4 × 10-3 S·cm−1 at 80℃ and 5.5 × 10-5 at RT. The results demonstrate that the interfacial phase also enhances the electrochemical and cycle stability of CSEs.