Electrolytes for Li-ion cells in low temperature applications

Prototype AA-size lithium-ion cells have been demonstrated to operate effectively at temperatures as low as -30 to -40/spl deg/C. These improvements in low temperature cell performance have been realized by the incorporation of ethylene carbonate-based electrolytes which possess low melting, low viscosity co-solvents, such as methyl acetate, ethyl acetate, /spl gamma/-butyrolactone, and ethyl methyl carbonate. The cells containing a 0.75 M LiPF/sub 6/ EC+DEC+DMC+EMC (1:1:1:1) electrolyte displayed the best performance at -30/spl deg/C (>90% of the room temperature capacity @/spl sim/C/15 rate), whereas, at -40/spl deg/C the cells with the 0.75 M LiPF/sub 6/ EC+DEC+DMC+MA (1:1:1:1) and 0.75 M LiPF/sub 6/ EC+DEC+DMC+EA (1:1:1:1) electrolytes showed superior performance.