Molecular Engineering of Fluorinated Solvents Enables Practical Lithium Metal Batteries

ABSTRACT Developing cost‐effective electrolytes with tunable fluorination is critical for practical lithium metal batteries (LMBs), yet structure‐property relationships remain unclear. Here, we systematically engineer fluorinated derivatives of ethyl acetate (EA), elucidating how fluorination sites and degrees govern solvent stability, electrolyte properties, interfacial chemistry, and battery performance, thereby establishing key design principles. Experiments and theoretical calculations have demonstrated that even with alpha hydrogen, ethoxy‐fluorinated solvents exhibit excellent chemical stability toward lithium metal in terms of thermodynamics and kinetics, successfully resolving the dilemma encountered with acetyl‐fluorination. Among them, the 2,2‐difluoroethyl acetate (DFEA)‐based electrolyte achieves a freezing point below −100°C, high ionic conductivity, high Li Coulombic efficiency (98.59%), flame retardancy, and oxidative stability up to 5 V. A 45 µm Li||LiNi 0.9 Co 0.05 Mn 0.05 O 2 (∼5.5 mAh cm −2 ) full cell retains 84.6% capacity after 130 cycles, while a 1000 mAh Li||LiNi 0.8 Co 0.1 Mn 0.1 O 2 pouch cell delivers a high specific energy of 414.8 Wh kg −1 . The electrolyte also excels in low‐temperature performance (−30°C), thermal safety, and electric vertical take‐off and landing (eVTOL) applications. Our findings provide a complete molecular‐to‐system solution for next‐generation batteries.