Regulated interfacial stability by coordinating ionic liquids with fluorinated solvent for high voltage and safety batteries

Electrolyte is the key to improve the safety, cycle performance and temperature adaptation of lithium batteries. In this paper, we introduce a novel electrolyte that based on ionic liquids (ILs) 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide (PYR14-TFSI) and fluorinated solvent 1,1,1,3,3,3-hexafluoroisopropyl methyl ether (HFPM). HFPM can significantly reduce the viscosity of PYR14-TFSI and enhance the wettability with Celgard separators. In addition, the coordination of PYR14-TFSI and HFPM promotes the local dissolution of lithium nitrate and helps to form a stable cathode/anode interface film. The electrochemical test shows that the electrochemical window of the electrolyte can reach to 5.35 V. For the Li/LiNi0.6Co0.2Mn0.2O2 half cells, the capacity retention is 94% and the Coulomb efficiency is 99.9% after 100 cycles at 0.5 C. The uniform and dense interface film is characterized and confirmed by scanning electron microscopy and X-ray photoelectron spectroscopy, etc. Furthermore, the half-cell also exhibits good thermal stability at high temperature. Considering ILs and fluoroether are non-flammable solvent, this work may pave the way for designing future generation high-performance electrolyte for lithium batteries.