Molecular Synergy Engineering of Fluorinated Eutectic‐Based Polymer Electrolytes for Fast‐Charging and High‐Voltage Lithium Metal Batteries

Abstract Gel polymer electrolytes (GPEs) based on deep eutectic electrolyte (DEE) show great promise for safe, high‐energy lithium metal batteries (LMBs). However, interfacial instability and limited fast‐charging capability remain challenges. Herein, an in situ polymerized fluorinated eutectic‐based electrolyte (named PDEE−UBP) is developed through molecular synergy engineering. The DEE consists of trifluoroacetamide (TFA) with a strongly electron‐withdrawing group ─CF 3 and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). A stabilized interphase is constructed through a triangular additive synergy strategy, involving 2‐(3‐(6‐methyl‐4‐oxo‐1,4‐dihydropyrimidin‐2‐yl)ureido)ethyl methacrylate (UPyMA), lithium difluoro(oxalato)borate (LiDFOB) and tris(trimethylsilyl)phosphate (TMSP). The self‐healing function of UPyMA mitigates stress from lithium dendrite growth, improving lithium deposition uniformity. LiDFOB and TMSP promote the formation of a stable cathode electrolyte interphase. PDEE−UBP exhibits high ionic conductivity (2.83 mS cm −1 at 25 °C), wide electrochemical stability window (5.6 V vs Li/Li + ), and a high Li⁺ transference number (0.68). Its moderately coordinated solvation structure weakens Li + −solvent interactions, lowers Li + transport barriers, and enhances rate performance. Consequently, Li||LiFePO 4 (LFP) cells deliver excellent 10 C performance with 84.7% capacity retention over 1000 cycles. Li||LiCoO 2 (LCO) cells retain 92.7% after 1000 cycles at 3 C under 4.5 V. Additionally, PDEE−UBP demonstrates compatibility with 4.9 V LiNi 0.5 Mn 1.5 O 4 cathodes. This work offers a promising approach for developing high‐voltage, fast‐charging GPEs for LMBs.