Molecular Engineering of Fluorinated Nitriles as Self-Passivating Electrolyte for High Voltage Lithium Metal...

Electrolyte engineering is essential for developing high-voltage lithium metal batteries (HV-LMBs). Nitrile-based compounds are one of the most promising electrolyte solvents with high chemical and oxidative stability, but their low stability against lithium metal anode is a notorious problem that hinders its practical applications. Herein, through molecular engineering of modulating the fluorination degree, partially fluorinated nitrile compounds were first reported, enabling self-passivation toward lithium metal anodes. Both theoretical calculation and experimental results revealed that the mono-fluorinated nitrile (F1EON) based solvent not only exhibits a horizontal adsorption configuration on the lithium metal surface, resulting in the spontaneous formation of a dense LiF passivation layer, but also forms a unique tridentate solvation structure, thereby inducing a LiF-rich cathode electrolyte interphase. Consequently, the 4.6 V high-voltage Li||LiCoO₂ cells with this F1EON-based electrolyte demonstrates robust cycling performance of 80.5% capacity retention after 350 cycles at 0.5 C and high-rate performance of 90.5% after 200 cycles at 4 C. This design strategy provides a promising approach for future exploration of advanced electrolytes for HV-LMBs.