Experimental evaluation of the performance of the sodium metal chloride battery below usual operating temperatures

The high operating temperature of the sodium metal chloride battery limits the possible applications of this storage technology. In this study, the performance of a 3.65 kWh (80 Ah, 48 V) battery at temperatures as low as 240 °C is measured and the efficiency at different discharge currents, cycling frequencies and operating temperatures is examined. The total available capacity of a 40 Ah string at 240 °C when discharging with 0.1C is found to be just 1 Ah smaller compared to 275 °C, which is the nominal operating temperature of the battery. However it is shown that low temperatures have a big impact on the charge duration. Starting from 20% SOC (state-of-charge) the duration of charging until the fulfillment of the end-of-charge criterion at 240 °C is 25 h with the quickest charging regime (0.25C, 2.7 V/cell) whereas until 90% SOC 7.6 h are required. At a limited SOC operation window from 20% to 90% the total daily efficiency of the 3.65 kWh battery is higher at 240 °C compared to 275 °C and increases from 69% if one cycle is performed daily with 0.175C discharge current to 81% for two cycles with the same discharge rate.