Low Temperature Operation of the Cell Na/β"-Alumina/S(IV) in AlCl3-NaCl Melt

Abstract

The cell Na/β"-alumina/S(IV) in AlCl3-NaCl melt had been operated almost exclusively in the temperature range 180o to 250oC. Lower temperature operation was explored using the acidic region of the AlCl3-NaCl phase equilibrium, which has a eutectic at 108oC, and the first step in the S(IV) discharge process (OCV > 4.2 V). When the commonly used low surface area current collector was used in the cathode, cell operation below 150oC led to only partial utilization of cell capacity. However, using a cathode constructed with a high surface area current collector (RVC) and operated exclusively in acidic melts, the cell was cycled down to 120oC. It was operated with essentially full capacity and produced ≈100% coulombic efficiency. Energy efficiency at 120o was 87%. Cell operation at and below 115oC led to incomplete and irreproducible discharges. Low temperature operation of this cell can minimize or eliminate corrosion of cathode seal components and extend cell life-time. Because of these favorable properties this cell can find applications in energy storage as well as in downhole oilfield tools.