Composite Gel Electrolytes with Ion-Mediated Compatibilization and Matrix-Assisted Conduction for Wide-Temperature Lithium Metal Batteries.

Abstract

Gel polymer electrolytes (GPEs) with solvent-in-polymer structure typically encounter a trade-off between ionic conductivity and mechanical properties. This challenge has not been adequately addressed by conventional single-material, miscible polymers, or polymer/ceramic composite electrolytes. Herein, the phase consistency of composite GPE matrix, which contains polymer blends of "soft" poly(vinylidene fluoride-co-hexafluoropropylene) (PVHF) and "hard" polyether-ether-ketone (PEEK), is enhanced by ion-mediated compatibilization through the incorporation of lithium sulfonate groups. In addition, the electrolyte's ionic environment is optimized by the pendent lithium sulfonate positioned at the interface between polymer-rich and solvent-rich domains, thus achieving high ionic conductivity of 1.87 mS cm^-1 at 20 °C and 1.28 mS cm^-1 at -20 °C via the matrix-assisted conduction. As a consequence, the composite gel electrolyte confers the Li||LiFePO₄ battery with high discharge capacity of 157.0 mAh g^-1 at 1 C and capacity retention of 90.7% after 1500 cycles, and superior electrochemical performance under harsh conditions, including high rate of 5 C (96.0% capacity retention after 1000 cycles), extreme temperatures from -20 °C to 80 °C, and in conjunction with 30-µm lithium metal anode. This work advances the development of high-performance gel polymer electrolytes through innovative nanostructure and molecule design.