Polymer-in-salt electrolyte enables ultrahigh ionic conductivity for advanced solid-state lithium metal batteries

Polymer solid-state electrolyte (SSE) still confronts low room-temperature ionic conductivity for broad appli-cation in solid-state batteries. Herein, an eye-catching polymer-in-salt PVDF-HFP/LiFSI/LLZTO composite SSE with ultrahigh ionic conductivity is elaborately designed. In this electrolyte system, poly (vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) matrix provides the electrolyte well mechanical property and Li salt solubi-lity, high content of lithium bis(fluorosulfonyl) imide (LiFSI) with low dissociation energy contributes to extra Li+ hopping transmission path, and Li6.4La3Zr1.4Ta0.6O12 (LLZTO) filler endows the SSE enhanced electro-chemical stability. As a consequence, this polymer-in-salt composite SSE exhibits an ionic conductivity of 1.67 x 10-3 S cm- 1 and superior critical current density (CCD) of 3.2 mA cm-2 at room temperature (25 degrees C). Moreover, Li||Li symmetric battery holds uniform polarization over 240 h at 0.3 mA cm-2 and 0.3 mAh cm-2. And Li|| LiFePO4 full cell exhibited a high capacity retention ratio of 97.2% with Coulombic efficiency of 99.75% after 300 cycles.