Li-ion Battery Electrolytes Designed for a Wide Temperature Range

Abstract : In recent years, the applications for Li-ion batteries have expanded dramatically. Having displaced NiMH in the consumer electronics market and beginning to displace NiCd in the power tool market, Li-ion batteries are being actively developed for HEVs and the military/aerospace applications, where the required operational temperature range is significantly broader. To date, the single technological bottleneck limiting the operation of the Li-ion battery over a wide temperature range is the electrolyte itself. In particular, Li-ion battery performance steeply declines as the operating temperature dips below -10 deg C. Additionally, battery characteristics rapidly deteriorate at temperatures above 60 deg C. We report on the development of a new family of Li-ion battery electrolytes designed to operate over a wide temperature range. These electrolytes possess excellent transport properties along with high thermal stability. Li-ion cells incorporating new electrolyte formulations may now be discharged at rates as high as C/4 at -50 deg C. Further, such cells demonstrate long cycle life both at room temperature and at temperatures as high as 80 deg C. In this paper we consider the operational temperature requirements for various applications and discuss the temperature limitations of state-of-the-art Li-ion battery electrolytes. We then present our results on the cycle life and charge/discharge characteristics of a new family of electrolytes over a wide temperature range. Finally, we consider potential compromises between Li-ion battery rate capability at low temperatures and high temperature cycle life.