Evaluation of the Li(Si)/FeS(2) and Li(Si)/CoS(2) Couples for a High-Voltage, High-Power Thermal Battery

A detailed evaluation of the Li(Si)/FeSz and Li(Si)/CoSz couples was undertaken to determine which was better suited for use in a thermal battery with challenging high-voltage and highpower requirements. The battery was to produce a minimum voltage of 205 V during pulses of 36 A superimposed on a 6-A background load. The final design called for two 96-cell batteries in series, with each providing 1.1 kW background load, with peak power levels of 6.7 kW. The battery lifetime was to be 5 min. Since it was not possible to duplicate the desired complex waveform exactly, an alternate approximating constant-current load profile was used. Single-cell tests were carried out at temperatures of 400°C – 5500C using the standard LiC1-KCl eutectic, the low-melting LiBr-KBr-LiF eutectic, and the all-lithium LiC1-LiBr-LiF minimummelting electrolyte. These screening studies were then extended to 10-cell and 25-cell batteries at the same equivalent load conditions. Both 1.25’’-dia. and 2.25’’-dia. stacks were tested. Based on these tests, the best overall results were obtained using the all-Li electrolyte with the COS2 cathode and flooded anodes. The next best electrolyte was the low-melting electrolyte. A preliminary test with a 95-cell battery showed better performance than what was expected based on results of 10and 25-cell tests, due to lower cell resistance.