Tailoring electrolyte phase separation for high-rate solid-state lithium metal batteries

Solid polymer electrolytes are attractive for solid-state lithium metal batteries due to their flexibility and safety but suffer from low ionic conductivity and unstable interfaces. Conventional polymerization-induced phase separation strategies enhance ion transport yet rely on external components such as deep eutectic solvents or ionic liquids, increasing cost and complexity. Here, a LiTFSI-mediated in-situ polymerization strategy is developed to induce controllable phase separation in a poly(vinylene carbonate) matrix using a single solvent. Electrostatic interactions between lithium salts and the polymer drive self-organized dual phases that combine mechanical robustness with efficient ion transport. The resulting PVC electrolyte achieves a tunable ionic conductivity from 0.20 to 0.92 mS/cm at 25 °C and a high lithium-ion transference number of 0.78. Li|PVC-24h | LiFePO₄ cells achieve 121.4 mAh/g at 5 C (12 min) with 90% capacity retention after 4000 cycles, demonstrating a scalable approach for high-performance polymer electrolytes.