Quasi‐Solid‐State Composite Electrolytes with Multifunctional 2D Molecular Brush Fillers for Long‐Cycling Lithium Metal Batteries^†

Comprehensive Summary The ever‐growing demand for next‐generation high‐energy‐density devices drives the development of lithium metal batteries with enough safety and high performance, in which quasi‐solid‐state composite electrolytes (QSCEs) with high ionic conductivity and lithium ion transference number ( ) are highly desirable. Herein, we successfully synthesize a kind of two‐dimensional (2D) molecular brush (GO‐ g ‐PFIL) via grafting poly(ionic liquid) side‐chain (poly(3‐(3,3,4,4,4‐pentafluorobutyl)‐1‐vinyl‐1 H ‐imidazol‐3‐ium bis(trifluoromethanesulfonyl)imide), denoted as PFIL) on the surface of 2D graphene oxide (GO) sheet. GO‐ g ‐PFIL is used as multifunctional filler to prepare novel composite membranes and corresponding QSCEs ( e.g ., QSCE‐PH/GPFIL3/P). The as‐obtained QSCE‐PH/GPFIL3/P integrates features of PFIL side‐chain‐enhanced lithium ion conduction, poly(vinylidene fluoride‐ co ‐hexafluoropropene) backbone‐induced flexibility, and GO‐strengthened mechanical property. As a result, our ultrathin (21 μm) self‐supporting QSCE‐PH/GPFIL3/P exhibits high ionic conductivity (3.24 × 10 −4 S·cm −1 ) and excellent (0.82) at room temperature, and Li/LFP full cell with QSCE‐PH/GPFIL3/P shows superior rate performance (high specific capacities of 79 mAh·g −1 at 30 °C and 5 C) and excellent cycling performance (high capacity retention of 91% after 500 cycles at 80 °C and 1 C).