In Situ Polymerized Fluorine‐Free Ether Gel Polymer Electrolyte with Stable Interface for High‐Voltage Lithium Metal Batteries

Abstract Lithium metal batteries offer increased energy density compared to traditional lithium‐ion batteries. Commercial carbonate‐based electrolytes are incompatible with lithium metal anodes, while ether‐based electrolytes, though more suitable, tend to degrade under high potentials. Here, a fluorine‐free ether‐based gel polymer electrolyte (FEGPE) has been developed via incorporating lithium bis((trifluoromethyl)sulfonyl)azanide (LiTFSI) as lithium salt, 1,2‐dimethoxyethane (DME) and 1,3‐dioxolane (DOL) as solvents, and indium trifluoromethanesulphonate (In(OTF) ₃ ) as an initiator. DME is used to promote dissolution of the In(OTF) ₃ in DOL, along with enhanced ion transport of the FEGPE. Compared to traditional ether‐based liquid electrolytes, the FEGPE demonstrates significantly improved antioxidant decomposition ability at high potentials, stemming from intermolecular hydrogen bond formation and decreased lone‐pair electron activity of ether oxygen. Additionally, the FEGPE reduces the lithium deposition energy barrier and enables a stable electrolyte/electrode interface by forming Li‐In alloys and LiF components in solid electrolyte interphases. In turn, Li|FEGPE|LiFePO ₄ cells exhibit a high initial capacity of 151 mAh g ⁻¹ at 0.5 C, with an outstanding capacity retention of 97% over 300 cycles. For high‐voltage cathodes, Li|FEGPE|LiN _0.8 iCo _0.1 Mn _0.1 O ₂ cells deliver an initial capacity of 167 mAh g ⁻¹ at 1 C, achieving a capacity retention of 75% over 500 cycles.