The effects of temperature on the electrochemical performance of sodium–nickel chloride batteries

Abstract Sodium–nickel chloride (ZEBRA) batteries are typically operated at relatively high temperatures ( 3  300 °C) to achieve adequate electrochemical performance. In the present study, the effects of operating temperature on the electrochemical performance of planar-type Na/NiCl 2 batteries were investigated to evaluate the feasibility of battery operation at low temperatures (£200 °C). The planar-type cell was able to be cycled at C/3 rate at as low as 175 °C despite higher cell polarization. Overall, low operating temperature resulted in a considerable improvement in the stability of cell performance. Cell degradation was negligible at 175 °C, while 55% increase in end-of-charge polarization was observed at 280 °C after 60 cycles. SEM analysis indicated that the degradation at higher temperatures was related to the particle growth of both nickel and sodium chloride. The cells tested at lower temperatures (£200 °C), however, exhibited a sharp drop in voltage at the end of discharge due to the diffusion limitation, possibly caused by the limited ionic conductivity of catholyte or the poor wettability of sodium on the β″-Al 2 O 3 solid electrolyte (BASE). Therefore, improvements in the ionic conductivity of catholyte and sodium wetting as well as reduction in the ohmic resistance of BASE are required to enhance the battery performance at low temperatures.