Diversifying Ion-Transport Pathways of Composite Solid Electrolytes for High-Performance Solid-State Lithium-Metal Batteries

Abstract

The application of composite solid electrolytes (CSEs) in solid-state lithium-metal batteries is limited by the unsatisfactory ionic conductivity underpinned by the low concentration of free lithium ions. Herein, we propose an interface design strategy where an amine silane linker is employed as a coupling agent to graft the Li₇La₃Zr₂O₁₂ (LLZO) ceramic nanofibers to the poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) polymer matrix to enhance their interaction. The hydrogen bonding between amino-functionalized LLZO (NH₂@LLZO) and PVDF-HFP not only effectively induces a uniform incorporation of high-content nanofibers (50 wt %) into the polymer matrix but also furnishes sufficient continuous surfaces to weaken the complexation between PVDF-HFP and Li-ion carriers. Additionally, introduction of the hydrogen bond and Lewis acid-base interplay strengthens the interfacial interactions between NH₂@LLZO and lithium salts that release more free lithium ions for efficient interfacial transport. The impact of the linker's structure on the dissociation capacity of lithium salts is systematically studied from the steric effect perspective, which affords insights into interface design. Conclusively, the composite solid electrolyte achieves a high ionic conductivity (5.8 × 10^-4 S cm^-1) by synergy of multiple transport channels at ceramic, polymer, and their interface, which effectively regulates the lithium deposition behavior in symmetric cells. The excellent compatibility of the electrolyte with both LiFePO₄ and LiNi_0.8Co_0.1Mn_0.1O₂ cathodes also results in a long lifetime and a high rate capability for full cells.