Highly Ion-Selective Gel Polymer Electrolyte Facilitates Stable 4.6 V LRMO-Based Solid-State Lithium Metal Batteries

To achieve high energy density, solid-state lithium metal batteries with Li-rich manganese oxide cathodes are promising but constrained by the limited electrochemical window of polymer electrolytes and poor interfacial compatibility. Herein, we report a highly ion-selective gel polymer electrolyte (GPE) fabricated via in situ copolymerization of vinylene carbonate (VC) and hexafluorobutyl methacrylate (HFBMA) with magnesium methacrylate (MgMA) as a functional cross-linker. The strong Lewis acid Mg center anchors free anions via Mg-TFSI interaction, raising the Li+ transference number to 0.52. This electrolyte promotes a robust, inorganic-rich solid electrolyte interphase (SEI) containing Li-Mg alloy, LiF, and Li3N, suppressing dendrites and interfacial side reactions. Consequently, the Li||LRMO full batteries exhibit an ultrahigh initial Coulombic efficiency of 98.41% and an initial specific capacity of 224.8 mAh g-1 at 0.5 C, demonstrating superior interfacial compatibility and long-term cycling stability for high-voltage SSLMBs.