Li[C2F5BF3] as an electrolyte salt for 4 V class lithium-ion cells

Lithium pentafluoroethyltrifluoroborate, Li[C2F5BF3] (LiFAB), was prepared by a facile metathesis reaction between high-purity K[C2F5BF3] and LiBF4 in dimethyl carbonate with almost quantitative yield. It was characterized by H-1-, F-19, B-11-, Li-7-NMR, and elemental analysis. In nonaqueous solvents, LiFAB showed higher electrolytic conductivities than LiBF4 due to the weaker coordinating ability of FAB(-). Compared with LiPF6, it showed a lower electrolytic conductivity in room-temperature region, and a higher conductivity in low-temperature region (T < -10degreesC). The performances of LiFAB were evaluated in comparison with LiPF6 and LiBF4 by using Li/graphite and Li/nickel-based oxide half-cells and Li-ion cells. The results showed that LiFAB could afford comparable performances to LiPF6 and much better performances than LiBF4. (C) 2005 The Electrochemical Society. All rights reserved.