Y. Eineli et al., LI-ION BATTERY ELECTROLYTE FORMULATED FOR LOW-TEMPERATURE APPLICATIONS, Journal of the Electrochemical Society, 144(3), 1997, pp. 823-829
Low-temperature (<0 degrees C) applications of Li-ion batteries have p
rompted the search for improved, high-conductivity electrolytes. Becau
se the performance of the carbonaceous anode is highly sensitive to ch
anges in electrolyte composition, we focused our efforts on this elect
rode. Electrolytes containing LiAsF5, LiPF6, LiN(SO2CF3)(2) [lithium b
is(trifluoromethanesulfonyl)imide] , or LiIm, and LiC(SO2CF3)(3) [lith
ium tris(trifluoromethanesulfonyl)methide], or LiMe, in methyl formate
(MF)-ethylene carbonate (EC) solvent mixtures were tested in lithium-
graphite half-cells. The graphite electrodes could be cycled at ambien
t temperature with high reversible capacity. The best supporting elect
rolyte was found to be LiAsF6, and the presence of a high concentratio
n of ethylene carbonate and up to 300 ppm H2O in the solution consider
ably increased the reversible capacity upon cycling. The conductivity
values of a binary solvent mixture of methyl formate and ethylene carb
onate containing LiAsF6 or LiMe were measured between -40 degrees C an
d room temperature. Graphite electrodes cycled at -2 degrees C in thes
e electrolytes obtained reasonable reversible capacity, approaching 50
%.