Practical High‐Voltage Lithium Metal Batteries Enabled by the In‐Situ Fabrication of Main‐Chain Fluorinated Polymer Electrolytes

Polymer electrolytes are crucial for advancing safe, high-energy-density lithium batteries. Therefore, such electrolytes must possess stability with high-voltage cathodes and lithium metal, ensuring efficient interfacial contact and high room-temperature ionic conductivity. In this study, we present a novel main-chain fluorinated polymer electrolyte, FEOP, synthesized through cationic ring-opening polymerization. FEOP integrates high oxidative resistance of polytetrafluoroethylene with lithium metal compatibility of polyether, achieving an oxidation potential of up to 5.6 V and an anion-involved solvation structure. The exceptional stability enables NCM811 cells to deliver an impressive cycling life of 2000 cycles at 1 C up to 4.5 V. Furthermore, at ultra-high cut-off voltages of 4.7 and 4.9 V, both NCM811 and LNMO cells demonstrate stable cycling over 700 cycles, marking the longest lifespan for polymer-based batteries under these challenging conditions. Moreover, 4.7 V solid-state lithium metal pouch cells incorporating FEOP exhibit an energy density of 405.3 Wh kg^-1 and maintain stable cycling over 70 cycles, while successfully passing industry-standard nail penetration tests. Moreover, FEOP demonstrate excellent compatibility with ultra-high-loading electrode (70 mg cm^-2), achieving an exceptional areal capacity of 16.2 mAh cm^-2. These results provide a solid foundation for designing practical electrolytes that enable next-generation high-energy-density and high-safety solid-state batteries.