UV-Cross-Linked Composite Polymer Electrolyte for High-Rate, Ambient Temperature Lithium Batteries

We report an innovative cross-linked composite polymer electrolyte (CPE) based on the garnet-type ceramic super Li+ ion conductor, Li7La3­Zr2O12 (LLZO), that is encompassed in a supersoft poly­(ethylene oxide)/tetraglyme matrix. UV-induced, facile and solvent-free cross-linking process ensures flexible and self-standing CPEs, which are nonflammable and perfectly shape-retaining under thermal/mechanical stress. The CPEs exhibit high ionic conductivity, exceeding 0.1 mS cm–1 at 20 °C, suitable for ambient and subambient temperature operation. Lab-scale lithium metal polymer cells assembled with LiFePO4-based composite cathode and the optimized CPE deliver full capacity at low current rates and outstanding specific discharge capacity of 115 mAh g–1 at 1C rate and ambient temperature. Remarkably, the lithium metal cell can run for hundreds of galvanostatic cycles (>400) with low overpotential, limited fading, and excellent Coulombic efficiency (>99%), which postulates the practical application of the newly developed CPEs as truly solid separating electrolytes in high-power energy storage technologies, assuring safety and performance in a wide range of operating conditions.