Performance and thermal behavior of sodium-sulfur cell under high current density operations

Performance and thermal behavior of the sodium-sulfur cell of a central sodium tube type under high current density operations are investigated by thermal modeling and calculations and experimental verification. The following are clarified by comparing calculated results with experimental ones: (i) the cell temperature varies widely during the charge-discharge operations, and it becomes maximum at the end of discharge; (ii) a hypothetical maximum of the energy efficiency is estimated by the calculation; (iv) though the thermal stress applied to the beta″-alumina solid electrolyte tube is small, the thermal fatigue of sealing parts of the cell and corrosion of a metal container of the sulfur electrode are accelerated under high current density operations; (v) dynamic behavior of the cell when the cell is short-circuited is investigated by experiments and calculations, and it is indicated that, in consequence of the high short-circuit current, the temperature rise becomes extremely high depending on the external resistance and the starting point of discharge depth. The induced thermal stress is small even then. The present method of the simulation is utilized to determine proper operating conditions of the cell under high current density operations and to assess the safety in the case that the cell is accidentally short-circulated.