Dual functional composite solid electrolyte constructed by double-layer sulfonated polyethersulfone (SPES)/poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) nanofiber membrane in high-performance all-solid-state lithium metal batteries

The successful implementation of polymer electrolytes in next-generation all-solid-state lithium metal batteries (ASSLMBs) is impeded by their low ion conductivity and weak resistance to lithium dendrites. Herein, a composite solid electrolyte (D-SPES-PH-PEO) with dual reinforcement effects is obtained by combining PEO matrix with a double-layer sulfonated polyethersulfone (SPES)-poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) nanofiber membrane. The SPES nanofiber membrane acts as a hopping site for ion transport by utilizing the electronegativity and Coulombic force of its own –SO3H groups, reducing the energy barrier of the D-SPES-PH-PEO electrolyte. Profiting from the existence of C-F bond, PVDF-HFP nanofiber membrane specializes in generating a protective SEI layer on the lithium anode. Moreover, such a functional membrane not only effectually constructs a three-dimensional ion transport channel by fabricating ion conductive substructures, but also enhances the mechanical strength of the electrolyte. Consequently, the D-SPES-PH-PEO electrolyte is equipped with a high ion conductivity of 7.41 × 10−5 S cm−1 at 30 °C and high tensile strength of 8 MPa. Furthermore, Li/Li symmetric battery incorporating D-SPES-PH-PEO electrolyte enables a stable cycle for 2500 h at 0.2 mAh cm−2. The D-SPES-PH-PEO electrolyte represents outstanding compatibility with LiFePO4 and high-voltage LiNi0.8Mn0.1Co0.1O2 (NMC811) electrodes. Especially, the LiFePO4/D-SPES-PH-PEO/Li pouch cell indicates an initial specific capacity of 146.7 mAh g−1 and the NMC811/D-SPES-PH-PEO/Li pouch cell reaches a maximum capacity of 178.5 mAh g−1. This study emphasizes the importance of double reinforcement of ion conduction and anode protection on solid electrolytes.