Abstrakt
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 LiPF(6), were successfully tested as electrolytes for Li(2)FeSiO(4) cathodes operating at elevated temperatures of 60 degrees C. The electrolytes based on ionic liquids show good ionic conductivity (from 3.3 x 10(-3) to 4.5 x 10(-3) S cm(-1)) together with good electrochemical stability up to 5 V vs Li/Li(+).
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 LiPF(6) 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 Li(2)FeSiO(4) showed a slightly lower reversibility in ionic liquids when compared to a DEC:EC 1 M LiPF(6) electrolyte; at higher cycles the reversibility and the obtained capacity were comparable to the one obtained in a DEC:EC 1 M LiPF(6) 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.