Fluoroethylene Carbonate-Enabled Gel Polymer Electrolyte for Stable High-Voltage Lithium Metal Batteries

The stable operation of lithium metal batteries (LMBs) at high voltages is currently limited by the performance of conventional electrolytes. Fluoroethylene carbonate (FEC) exhibits unique physicochemical properties that positively impact interfacial chemistry, positioning it as a promising candidate to enhance the performance of LMBs. However, FEC is prone to the formation of corrosive HF under high voltage, which leads to the degradation of electrode interface. In this study, a hybrid gel polymer electrolyte (HGPE) based on pure FEC solvent with pentafluorophenyl methacrylate (PFPMA) monomer is presented to extend the voltage operating range. The PFPMA monomer forms a mixed-layer solid electrolyte interphase with lithium difluoro(oxalato)borate (LiDFOB) on electrode surface, effectively inhibiting the decomposition of FEC. The triangular synergistic strategy involving FEC, PFPMA, and polymer segments improves the transport of Li ions in FEC, achieving a high Li⁺ transference number of 0.87. The designed electrolyte demonstrates good compatibility with Li metal and stabilizes LiNi_0.8Co_0.1Mn_0.1O₂ (NCM811) cathodes. As a result, the Li||NCM811 battery based HGPE exhibits a capacity retention of 83.4% after 300 cycles and 74.2% after 400 cycles, under a cut-off voltage of 4.5 V. This study provides a promising strategy for the development of GPE for high-voltage LMBs applications.