Electrolyte based on 1-ethyl-3-vinylimidazolium bis(trifluoromethanesulphonyl)imide for Li-ion batteries

• Paper describes properties of IL electrolyte for lithium-ion batteries.
• 1 M LiNTf2 in EVImNTf2 electrolyte shows good compatibilities with LFP and graphite.
• LiFePO4/IL electrolyte/graphite cell shows a relatively high capacity of 125 mAh g−1 after 30 cycles.
• This performance is attributed to a higher stability of cation in the ionic liquid.

In this study, a new electrolyte for Li-ion batteries in the form of lithium salt solution in ionic liquid (IL) based on imidazolium cation with vinyl group is reported. This electrolyte was obtained by dissolution of solid lithium bis(trifluoromethanesulphonyl)imide (LiNTf2) in 1-ethyl-3-vinylimidazolium bis(trifluoromethanesulphonyl)imide (EVImNTf2). 1 M LiNTf2 in the EVImNTf2 electrolyte has good cathodic stability (the presence of the vinyl group) and flash point above 220 °C, which makes it practically non-flammable. The olivine-type lithium iron phosphate (LiFePO4, LFP) cathode and the graphite-lithium anode working together with the electrolyte were tested with the use of cyclic voltammetry (CV), galvanostatic charge/discharge cycles and electrochemical impedance spectroscopy (EIS). The surface morphology of electrodes was studied using scanning electron microscopy (SEM). Charge/discharge tests of LiFePO4/1 M LiNTf2 in the EVImNTf2/Li cell at different C rates exhibited a good specific capacity of 115 mAh g−1 and 110 mAh g−1 at 0.5 C and 1.0 C, respectively. The graphite anode showed good cyclability (307 mAh g−1 after 40 cycles) and coulombic efficiency (94%). The efficiency of the full LFP|electrolyte|G cell charging/discharging under study was high (ca. 125 mAh g−1 after 30 cycles).