Solvation Structure and Derived Interphase Tuning for High‐Voltage Ni‐Rich Lithium Metal Batteries with High Safety Using Gem‐Difluorinated Ionic Liquid Based Dual‐Salt Electrolytes

Abstract Stabilizing electrolytes for high‐voltage lithium metal batteries (LMBs) is crucial yet challenging, as they need to ensure stability against both Li anodes and high‐voltage cathodes (above 4.5 V versus Li/Li + ), addressing issues like poor cycling and thermal runaway. Herein, a novel gem‐difluorinated skeleton of ionic liquid (IL) is designed and synthesized, and its non‐flammable electrolytes successfully overcome aforementioned challenges. By creatively using dual salts, fluorinated ionic liquid and dimethyl carbonate as a co‐solvent, the solvation structure of Li + ions is efficiently controlled through electrostatic and weak interactions that are well unveiled and illuminated via nuclear magnetic resonance spectra. The as‐prepared electrolytes exhibit high security avoiding thermal runaway and show excellent compatibility with high‐voltage cathodes. Besides, the solvation structure derives a robust and stable F‐rich interphase, resulting in high reversibility and Li‐dendrite prevention. LiNi 0.6 Co 0.2 Mn 0.2 O 2 /Li LMBs (4.5 V) demonstrate excellent long‐term stability with a high average Coulombic efficiency (CE) of at least 99.99 % and a good capacity retention of 90.4 % over 300 cycles, even can work at a higher voltage of 4.7 V. Furthermore, the ultrahigh Ni‐rich LiNi 0.88 Co 0.09 Mn 0.03 O 2 /Li system also delivers excellent electrochemical performance, highlighting the significance of fluorinated IL‐based electrolyte design and enhanced interphasial chemistry in improving battery performance.