Performance of Li-ion cells with new electrolytes conceived for low-temperature applications

In an effort to develop a useful electrolyte for a Li-ion cell applicable i n a wide operation temperature, we have studied a number of ternary electro lytes containing a cyclic carbonate (ethylene carbonate (EC)), a linear car bonate (dimethyl carbonate (DMC), diethyl carbonate (DEC), or ethylmethyl c arbonate (EMC)), and a low-temperature freezing solvent (methyl acetate, et hyl acetate, isopropyl acetate, isoamyl acetate, or ethyl propionate (EP)). We have studied performance including cycle life of Li-ion cells containin g these electrolytes at various temperatures. The performance was various w ith various electrolyte compositions showing a significant effect of the lo w-temperature freezing solvents while the effect of the linear carbonates w as relatively minor. Cells containing an electrolyte of EC-DMC-MA showed an excellent initial performance at - 20 degrees C but it did not give a good cycle life compared with others. Two electrolyte compositions containing E P, EC-DEC-EP and EC-EMC-EP, showed the most attractive overall performance including initial performance at - 20 degrees C, cycle life and rate capabi lity at room temperature as well as 50 degrees C. (C) 2000 Elsevier Science S.A. All rights reserved.