Performance of a 10-cell LiA/psi//Metal sulfide battery

A 4kWh LiA/psi//FeS battery having a molten salt electrolyte was fabricated by Eagle-Picher Industries under contract to ANL and was tested through 150 deep discharge cycles at ANL. The battery module contained ten series connected cells having theoretical capacities of 394 Ah. When fully charged, the battery gave 340 Ah at a 70-A discharge for a cell specific energy of 90 Wh/kg. Battery discharge was terminated when the weakest cell reached a 0.9-V cutoff and was terminated on bulk charge when the strongest cell reached a 1.55-V cutoff. The battery was fully charged through equalization after about every 8 cycles. Between charge equalizations, the battery capacity loss rate was about 0.75% of the fully charged capacity per cycle. Normal capacity fade rate for individual cells is 0.02-0.03% per cycle. The higher loss rate for the battery resulted from capacity and coulombic efficiency differences among the cells. During the last third of battery life three cells developed internal short circuits by a common failure mode.