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|LiFePO₄ 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_0.8iCo_0.1Mn_0.1O₂ cells deliver an initial capacity of 167 mAh g⁻¹ at 1 C, achieving a capacity retention of 75% over 500 cycles.