Mixtures of ionic liquid and organic carbonate as electrolyte with improved safety and performance for rechargeable lithium batteries

Highlights: → Mixtures of PC, PYR14TFSI and LiTFSI as electrolyte for lithium-ion batteries. → Mixtures with a high ionic liquid (IL) content are non-flammable. → Al corrosion potential is shifted to higher potentials by the addition of IL. → Cycling stability of a Li/LiFePO4 cell at 60 oC is improved by the addition of IL. - Abstract: In this paper we report the results of physical-chemical and electrochemical investigations performed on ternary mixtures of the room temperature ionic liquid (IL) N-butyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (PYR14TFSI), propylene carbonate (PC), and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) as electrolyte for lithium-ion batteries. The thermal stability, ionic conductivity, viscosity and electrochemical stability windows of all considered mixtures were investigated and compared with those of electrolytes based on the pure PYR14TFSI and PC. The mixtures were also used as electrolyte in combination with LiFePO4-based electrodes. The specific capacity and cycling stability of these systems were investigated at different C-rates, both at room temperature and 60 oC.