Lithium-ion (Li-ion) batteries are attractive candidates for use as power sources in aerospace applications because they have high specific energy ( up to 200 Wh/kg) and energy density (~ 500 Wh/L) and long cycle life (1,000 ? 30,000 cycles currently depending on the depth of cycling). However, at temperatures below about ?10o
C, their charge/discharge performance is severely degraded which hinders their use in deep space and planetary missions. This decrease in performance may be due to the precipitation of ethylene carbonate (EC) at low temperatures, which may prevent the migration of Li+ ions between the electrodes during charge and discharge. We propose to determine the cause of the EC precipitation. Appropriate electrolyte systems will be designed to prevent phase separation of the electrolyte at low temperatures during charge and discharge.