Tailoring Intermolecular Chemistry and Interphases via F, N‐Functionalized Polymer Matrix in High‐Flash‐Point Ether‐Ester Hybrid Electrolytes for Intrinsically Safe Quasi‐Solid‐State Li Metal Batteries

ABSTRACT In situ polymerized quasi‐solid‐state electrolytes (QSEs) are promising for lithium metal batteries (LMBs) yet face challenges regarding high‐voltage stability and kinetics. Herein, a novel ether‐ester hybrid QSE is achieved through the in situ copolymerization of 2,2,2‐trifluoroethyl acrylate (TFEA) and 2‐isocyanatoethyl methacrylate (IEM) within a tetraethylene glycol dimethyl ether (G4)/fluoroethylene carbonate (FEC) solvent system. This design leverages synergistic interactions between the functionalized polymer matrix (─CF 3 and ─N═C═O) and liquid components. The incorporation of FEC and the regulatory effect of the polymer backbone tailor the Li + solvation structure toward an anion‐rich configuration, which gives rise to a robust, antioxidative, and inorganic‐rich interphase. Furthermore, hydrogen bonding interactions effectively immobilize PF 6 − anions and free G4 molecules, thereby elevating the Li + transference number and enabling the electrochemical stability window over 4.8 V (vs. Li + /Li). The QSE exhibited a high room‐temperature ionic conductivity of 2.2 × 10 −3 S cm −1 . Consequently, 4.2 V Li|| LiFePO 4 (LFP) cells demonstrate 93% capacity retention over 1,000 cycles, while 4.5 V Li||NCM811 (NCM811) cells retain 80% over 300 cycles. A specific energy of 302.64 Wh kg −1 is attained in a 2 Ah Li||NCM811 pouch‐type cell. These findings highlight tailored molecular design and controlled interactions as a viable route for advancing high‐energy‐density quasi‐solid‐state batteries.