Understanding the influencing factors of porous cathode contributions to the impedance of a sodium-nickel chloride (ZEBRA) battery

Abstract

Molten-sodium beta-alumina batteries including sodium–sulfur (NAS) and sodium-metal chloride (ZEBRA) batteries have been considered as promising candidates for reliable low-cost stationary energy storage devices. The structural parameters of the porous cathode wetted by NaAlCl4 have been proved to be one of the important reasons for the degradation of ZEBRA batteries. Herein, the influencing factors of porous cathode on the impedance of Na–NiCl2 battery are investigated in detail. The interface between the NaAlCl4 catholyte and Ni/NaCl cathode material and the ratio of the conductive components in the cathode are discussed in this paper. Based on the wettability results of each component of the cathode material at different porosities and temperatures, the wetting behavior between NaAlCl4 and the porous cathode is summarized. Both the porosity and metal ratio of the cathode need to be considered in order to achieve the optimal catholyte/cathode material interface and minimum operating impedance. The proposed cathode parameters are porosity greater than 24% and conductive component ratio of 1.5 at NaAlCl4 ratio of 1.75. This work provides a quantitative guidance and deep understanding for the material design of ZEBRA battery cathodes.