“Synergistic Competition” Molecular Design Enables High‐Voltage Polyether Electrolytes for Lithium Metal Batteries

ABSTRACT Polyether electrolytes based on in situ polymerization of 1,3‐dioxolane (DOL) are promising owing to their high ionic conductivity and good compatibility with lithium metal anodes, yet their narrow electrochemical window and poor thermal stability limit high‐voltage, high‐safety applications. Herein, a novel polyether‐based quasi‐solid‐state electrolyte (PDEG) featuring both high‐voltage stability and enhanced safety is developed via in situ copolymerization of DOL with a bisphenol S epoxy resin (DEGBS). The sulfone groups and benzene skeleton in PDEG construct a unique “synergistic competition” solvation structure that optimizes Li ⁺ coordination, immobilizes anions, and promotes an inorganic‐rich solid electrolyte interphase. Consequently, PDEG delivers a high ionic conductivity of 0.757 mS cm ^{− 1} at 25°C, a high Li ⁺ transference number of 0.80, and a wide electrochemical window of 5.3 V. Li||Li symmetric cells operate stably for over 350 h even at a high areal capacity of 5 mAh cm ^{− 2} . LiFePO ₄ ‐based full cells retain 80.8% capacity after 800 cycles at 1C with excellent thermal stability. Notably, Li||NCM811 cells maintain 84.1% capacity after 100 cycles at a high cutoff voltage of 4.5 V, while pouch cells achieve 80.9% retention after 100 cycles at 0.2C, demonstrating outstanding practical potential.