A preliminary evaluation of lithium batteries for extended-life continuous-operation applications

A test program of several ambient temperature lithium battery systems has been initiated. Its purpose is to provide both real-time and accelerated data to determine the suitability of these systems to operate continuously for extended periods of up to 10 years. The Li/CuO and Li/(CF x ) n systems are compared with the Sandia-modified Li/SO 2 system that is currently being used in applications requiring operation for up to five years. Preliminary results show the Li/CuO system to be stable over a wide range of temperatures (−40 to +70 °C) with a narrow performance band. Cell capacities ranged from 17 to 21 A h for spirally-wound D cells over the entire temperature range studied, for current drains up to several hundred milliamperes. The major drawback of the Li/CuO system is its low operating voltage coupled with a large voltage drop at the beginning of discharge. The Li/(CF x ) n system has a substantial temperature effect. At 70 °C, cells vented at currents above 100 mA due to the buildup of internal pressure, while at −40 °C, cells operated only at 20 mA or less. At all conditions evaluated, a voltage step occurred near the end of life. This step occurred after complete utilization of the carbon monofluoride in the cathode-limited cells, when electrolyte reduction began. Further development is needed to make this system a viable candidate for long-life applications. Specifically, a new electrolyte solvent and an anode-limited design are required. The modified Li/SO 2 cells gave a very consistent performance over the current and temperature range studied. Due to the large data base available for this system and the modifications to improve long-life capability (elimination of premature failure due to materials corrosion), Li/SO 2 remains the primary system for use in extended-life applications pending further developments in the evolution of the Li/CuO and Li/(CF x ) n designs.