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

Abstract 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 _0.8 Mn _0.1 Co _0.1 O ₂ 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/LiCoO ₂ cells. This work provides a feasible development strategy of QSPEs for practical long‐cycling high‐voltage LMBs.