Bidentate Phosphonate‐Functionalized Ionic Liquid Exhibiting Better Ability in Improving the Performance of Lithium‐Ion Battery

Abstract In this work, flame retarding phosphonate‐functionalized imidazolium ionic liquids (PFILs) were synthesized and employed as electrolyte additives for Li/LiFePO 4 half‐cells. Physical and electrochemical properties, including ionic conductivity, electrochemical properties, electrochemical oxidation limit, electrochemical impedance spectroscopy (EIS) and lithium‐ion transference number (T Li + ), were investigated. The results demonstrate that the addition of PFIL can improve the electrochemical performance of lithium‐ion batteries (LIBs). Hybrid electrolyte with 10 wt % bidentate phosphonate‐functionalized imidazolium ionic liquid (b‐PFIL) exhibits more excellent electrochemical oxidation stability (up to 4.77 V vs. Li/Li + ), capacity retention (87.3 % after 400 cycles) and rate capability. These improvements can be ascribed to the enhanced lithium‐ion transference number (T Li + ), which results from the stronger binding affinity between chelating b‐PFIL and LiPF 6 .