A PVDF‐Based Composite Solid Electrolyte Enabled by Carbon‐Free LiFePO 4 for Stable Lithium Metal Batteries

Abstract

Developing polymer‐based solid electrolytes with efficient Li + transport, electronic insulation, mechanical robustness, and stable electrode interfaces remains challenging for solid‐state lithium‐metal batteries. Here, a carbon‐free LiFePO 4 (LFP)/PVDF composite solid electrolyte is designed, where the intrinsically low electronic conductivity of LFP is transformed from a limitation for cathode applications into an electrolyte advantage. Unlike carbon‐coated LFP, carbon‐free LFP acts as an electronically insulating inorganic filler in the PVDF matrix, suppressing electron transport while promoting Li + migration through abundant LFP/PVDF interfaces. Optimized LFP50 exhibits an ionic conductivity of 4.89 × 10 −4 S cm −1 at 25°C, a Li + transport activation energy of 0.053 eV, an electronic conductivity on the order of 10 −10 S cm −1 , a 5.0 V oxidative stability window, and favorable mechanical properties. These features enable stable Li‐metal interfaces, as demonstrated by a critical current density of 6.2 mA cm −2 and uniform Li deposition. Furthermore, LFP50 provides lithium compensation through partial delithiation of cathode‐facing LFP particles, mitigating irreversible lithium loss. Without external pressure, Li|LFP50|LFP and Li|LFP50|NCM811 cells retain 93.8% and 80% capacity after 500 and 165 cycles, respectively. This work demonstrates carbon‐free LFP as a multifunctional filler strategy for regulating Li + transport, stabilizing electrode interfaces, and advancing solid‐state lithium‐metal batteries.