All‐Material Crosslinked Solid Polymer Electrolytes for High‐Performance and Flexible Lithium Metal Battery

Abstract Solid polymer electrolytes (SPE) offer advantages including compatibility with conventional electrolyte systems and mechanical flexibility; however, low ionic conductivity and high interfacial resistance present significant challenges. Here, systems are proposed that randomly crosslink all‐materials constituting SPE based on diazide and develop novel flexible SPEs by covalently networking fluorinated polymers and succinonitrile. This all‐material crosslinking reduces crystallinity of the constituents, thus simultaneously boosting ionic conductivity, mechanical elasticity, and adhesion strength. Solvent‐assisted conformal coating ensures complete contact with the lithium surface and completely wets the porous cathode. The SPE exhibits high ionic conductivities of 4.7 mS·cm⁻¹, lithium‐ion transference numbers of 0.64, and oxidation stability up to 5.29 V. It demonstrates stable lithium plating/stripping with ∼5 mV of overpotential over 1400 h in Li//Li tests and outstanding performance in Li//LFP flexible full cells, achieving discharge capacities of 136.5 mAh g⁻¹ at 3 C and maintained even after bending at 5 mm or cutting in half.