Performance of Sodium/Selenium Tetrachloride Secondary Batteries with Basic Chloroaluminate Melts

Abstract

A new rechargeable cell, liquid podium/sodium β′′-alumina tube/tetravalent selenium in basic AlCl₃-NaCl melts, has been investigated to develop a high performance battery for the load-leveling application. The cells with carbon felt positive current collectors were able to charge and discharge efficiently even in basic chloroaluminate melts saturated with sodium chloride, as shown in Fig.2. The melt composition at the discharging limit is about 30/70 of AlCl₃-NaCl molar ratio, which depends on the deposition of sodium chloride, a poor electronic conductor, on the positive current collector.
Lower polarization, especially at charging, was ob served in the cells No. CS-54 in Fig.2and CS-62 in Fig.4; their current collectors were totally dipped in the positive melts. The energy density of Na/Se(IV) cells usually exceeds 300 Wh/kg with low current densities at 225°C, as shown in Fig.3. One cell, No. CS-61, showed a high energy density of 415 Wh/kg as well as high turn-around efficiency.; it had been prepared to work theoretically within the melt composition range between 65/35 and 30/70, as shown in Table 1. The resistance of this cell is about 7.0 ohm/cm²-β′′-alumina at 225°C.
Some degradation of the percent utilization of tetravalent selenium and of energy efficiency with continuous charge discharge cycles was observed for the Na/Se(IV) cells with the carbon felt current collectors, as shown in Fig.6.