Properties of LiNiO2 cathode and graphite anode in N-methyl-N-propylpyrrolidinium bis (trifluoromethanesulfonyl)imide

Electrochemical properties of LiNiO2|Li and LiNiO2|graphite cells were analysed in ionic liquid electrolyte [Li+][MePrPyrr(+)][NTf2-] (based on N-methyl-N-propylpyrrolidinium bis(trifluoromethanesulphonyl) imide, [MePrPyrr(+)][NTf2-]) using impedance spectroscopy and galvanostatic techniques. The ionic liquid is incapable of protective solid electrolyte interface (SEI) formation on metallic lithium or lithiated graphite. However, after addition of VC, the protective coating is formed, facilitating a proper work of the Li-ion cell. Scanning electron microscopy images of pristine electrodes and those taken after electrochemical cycling showed changes which may be interpreted as a result of SEI formation. The charging/discharging capacity of the LiNiO2 cathode is between 195 and 170 mAh g(-1), depending on the rate. The charging/ discharging efficiency of the graphite anode drops after 50 cycles from an initial value of ca. 360 mAh g(-1) to stabilise at 340 mAh g(-1). The replacement of a classical electrolyte in molecular liquids (cyclic carbonates) with an electrolyte based on the MePrPyrrNTf(2) ionic liquid highly increases in the cathode/electrolyte non-flammability.