Fluorinated nitrile-based electrolytes with micelle-like solvation structure for high energy density lithium metal batteries

Lithium metal batteries (LMBs) coupled with high-voltage Ni-rich cathodes hold significant promise in meeting the increasing demand for high energy density. However, a prevalent issue faced by state-of-the-art electrolyte systems is the aggressive electrode–electrolyte reactions, particularly with both the lithium metal anode and high-voltage cathode. In the context of designing high performance electrolytes, electrolyte engineering is an effective approach to bridge electrolyte chemistry with interfacial interactions. In this study, we report an amphiphilic fluorinated nitrile, 3-(2,2,3,3,3-pentafluoropropoxy) propanenitrile (F5EON), to tune the Li + solvation structure by micelle-like electrolytes, in which the lithiophilic nitrile group within F5EON solvates Li + with low binding energy and the lithiophobic carbon-fluorine chain encapsulates solvent molecules around Li + . In contrast to its non-fluorinated counterpart, the amphiphilic F5EON promotes the involvement of fluoroethylene carbonate (FEC) and anions in the first Li + solvation sheath, resulting in a robust cathode–electrolyte interphase (CEI) enriched with LiF and –CN species, as manifested by molecular dynamics (MD) simulations and time-of-flight secondary ion mass spectrometry (TOF-SIMS). The high-voltage Li||NCM811 cells demonstrate good cycling stability, maintaining 67.2% capacity retention after 200 cycles at 4.7 V and 75% retention after 80 cycles at 55 °C under extreme conditions. These results are superior to the base electrolyte, which shows degradation after 100 cycles at 4.7 V and unstable cycling at 55 °C. This work provides valuable insights into designing high-voltage electrolytes for high-performance LMBs by tuning interfacial chemistry with an amphiphilic fluorinated nitrile solvent. • The amphiphilic F5EON exhibits excellent compatibility with lithium metal anode and enhances oxidative stability for high-voltage cathode. • Micelle-like solvation structure originates from the amphiphilic structure and δ(H + )-δ(F − ) intermolecular interactions. • LiF-rich SEI and –CN/LiF-rich CEI enable stable cycling of high energy density 4.7 V Li||NCM811 cells.