Development of advanced lithium-ion rechargeable cells with improved low temperature performance

Due to future plans to explore Mars and the outer planets, NASA has interest in developing lithium-ion rechargeable batteries that are capable of operating at low temperatures. To address these problems, we have initiated research focused upon the development of advanced electrolyte systems for lithium-ion cells with improved low temperature performance. Promising electrolyte solutions were selected based on conductivity and stability considerations and incorporated into C/LiCoO/sub 2/ cells for evaluation. The discharge capacity and rate capability as a function of temperature were evaluated in two types of lithium-ion cells, consisting of graphite-based systems with EC-based electrolytes and coke-based systems with PC-based electrolytes. Some of the experimental lithium-ion cells fabricated with these electrolytes were found to be capable of operating at temperatures as low as -30/spl deg/C (both charging and discharging at -30/spl deg/C) and provide more than 55% of the room temperature capacity. Cycle life testing of the these cells at -20/spl deg/C and at room temperature is in progress. Some of the cells have completed more than 500 cycles to date (100% DOD).