Robust and Antioxidative Quasi‐Solid‐State Polymer Electrolytes for Long‐Cycling 4.6 V Lithium Metal Batteries

Quasi-solid-state polymer electrolytes (QSPEs) have been considered as one of the most promising electrolytes for high-safety high-energy-density lithium metal batteries (LMBs). However, their inadequate mechanical properties and instability under high voltages pose significant challenges for practical applications. Herein, robust and antioxidative QSPEs are developed based on a polymer-brush-based rigid supporting film (BC-g-PLiMTFSI-b-PPFEMA, BC: bacterial cellulose, PLiMTFSI: poly(lithium (3-methacryloyloxypropylsulfonyl) (trifluoromethylsulfonyl)imide), PPFEMA: poly(2-(perfluorohexyl)ethyl methacrylate)). The robust BC nanofibril backbone can produce a highly porous supporting structure with outstanding mechanical strength. More importantly, the PLiMTFSI-b-PPFEMA side-chains can not only obviously increase the conversion ratio of easily oxidized monomers in QSPEs, but also possess strong interaction with unstable electrolyte components. With such QSPEs as solid-state electrolytes, the Li/LiNi_0.8Mn_0.1Co_0.1O₂ full cell with a high cathode loading (20.3 mg cm^-2) exhibits a specific discharge capacity of 200.7 mAh g^-1 at 0.5 C and demonstrates a long lifespan of 137 cycles with a highly retained capacity of 170.7 mAh g^-1 under a cut-off voltage of 4.5 V. More importantly, under a high cut-off voltage of 4.6 V, a high specific capacity of 147.0 mAh g^-1 after 187 cycles can be retained for solid-state Li/LiCoO₂ cells. This work provides a feasible development strategy of QSPEs for practical long-cycling high-voltage LMBs.