Electrochemical Behavior of Li[sub 2]FeSiO[sub 4] with Ionic Liquids at Elevated Temperature

Ionic liquids, 1-butyl-2,3-dimethylimidazolium bis(trifluoromethanesulfonyl)imide and 1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide with 0.7 M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) or 0.5 M , were successfully tested as electrolytes for cathodes operating at elevated temperatures of . The electrolytes based on ionic liquids show good ionic conductivity (from to ) together with good electrochemical stability up to 5 V vs . The electrochemical stability of electrolytes based on ionic liquids against an aluminum current collector was comparable to a diethyl carbonate:ethylene carbonate (DEC:EC) 1 M electrolyte and even better when the electrolytes were tested with blank electrodes (only aluminum current collector, carbon black, and binder). In the first cycle the electrochemical testing of showed a slightly lower reversibility in ionic liquids when compared to a DEC:EC 1 M electrolyte; at higher cycles the reversibility and the obtained capacity were comparable to the one obtained in a DEC:EC 1 M electrolyte. All electrochemical results show that LiTFSI can be used as a salt in ionic liquid-based electrolytes. These properties allow their potential application in large-scale lithium-ion batteries with improved safety.