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.