Electrochemical instability of bis(trifluoromethylsulfonyl)imide based ionic liquids as solvents in high voltage electrolytes for potassium ion batteries

The feasibility of four ionic liquids containing bis(trifluoromethylsulfonyl) imide anion with different cations, namely 1-butyl-1-methylpyrrolidinium, 1-butyl-3-methylimidazolium, 1-methyl-1-propylpyrrolidinium and 1-ethyl-3-methylpyridinium, as solvents in an electrolyte of potassium ion batteries has been examined in half-cells with Al, Al2O3 as well as with practical cathode and anode materials. In spite of the previous reports on stability of ionic liquids with this anion in the 5 V limit, intrinsic electrochemical instability has been observed here both at high and low potentials, thus the investigated compounds can hardly be implemented in potassium ion cells due to their reactive nature.