A high energy density cell operating at 250°C has been developed employing a liquid sodium anode, a beta alumina electrolyte, and a novel solid‐state cathode. The cathode consists of a partially chlorinated porous iron matrix, impregnated with a sodium ion conducting molten salt NaAlCl4 which acts as a pure electrolyte. The reversibility of the cell reaction has been proven and considerable progress has been made towards optimization of the cathode, demonstrating high energy and power density, long life (>1000 cycles), and a high degree of safety.

Medium‐temperature liquid sodium (ZEBRA) battery cells, employing solid transition metal dichloride cathodes, are under active development. This paper details key aspects of the development of a Ni, NiCl2 positive electrode, operating in NaAlCl4 molten salt electrolyte. Cells using these materials have achieved a high degree of reversibility and long cell life (>2000 cycles) and operate over the temperature range 200°–350°C. The cell has an open‐circuit voltage of 2.58V at 300°C and is an attractive contender for use in high‐energy and power density advanced batteries. Mention is made to the related Fe‐based electrode.

The stability of beta alumina in fully developed Zebra normalNa/FeCl2 cells under long‐term cycling has been proven. In the early stages of development of the normalNa/FeCl2 cell, some problems in the form of increased resistances were encountered under certain extreme conditions of temperature and voltage. While these difficulties have now been overcome in practical cells, the scientific investigation into the causes of the anomalous resistance behavior showed it to be related to the interaction of the beta alumina with constitutents of the positive electrode compartment. In particular, iron has been shown to enter beta alumina in the presence of an electric field when current is passing, if the cell is deliberately overheated. However, it was found that only the β (but not the β″) phase was modified by the incursion of iron. The resistance of the iron‐doped regions of the ceramic was very high. Chloroaluminate melts also irreversibly damage the beta alumina in the absence of an electric field, when FeCl3 or excess AlCl3 is present, by abstraction of Na+ ions, forming γ alumina.

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ChemInform Abstract A medium-temp. liquid sodium (ZEBRA) cell with a porous Ni,NiCl2 cathode that operates in a NaAlCl4 molten salt electrolyte is described and its electrochemical performance is studied in detail. Additions of sulfur to the NaAlCl4 electrolyte results in the development of a modified, high surface area, active metallic phase which is stable on charge/discharge cycling for many hundreds of cycles. The cells exhibit a high degree of reversibility and long cell life (> 2000 cycles) and operate in the temp. range 200-350 rc C. The cell has an open-circuit voltage of 2.58 V at 300 rc C and is an attractive candidate for use in high-energy and power density advanced batteries.

ChemInform Abstract A high energy density cell operating at 250 rc C has been developed employing a liquid Na anode, a beta alumina electrolyte, and a novel solid-state cathode consisting of a partially chlorinated porous iron matrix impregnated with NaAlCl4 molten electrolyte. This cell has the feature that all of the cathode reactants, i.e., Fe, FeCl2, and NaCl, are insoluble in the NaAlCl4 electrolyte and therefore remain in intimate contact with each other and the current collector. The reversibility of the cell reaction is demonstrated and considerable progress is achieved in optimization of the cathode. The cell has a specific energy of ≥ 130 Wh/kg at the 5 h rate, an open-circuit voltage of 2.35 V at 250 rc C, long life ( > 1000 cycles), and a high degree of safety.

In a previous publication (1) we showed that stainless steel undergoes corrosion in a sodium polysulfide melt when polarized cathodically (i.e., at the end of discharge in a Na/S cell). This basic electrochemical study of the sulfur/polysulfide cathode has been extended using specially designed electrochemical cells incorporating potential probes in the ca%hode. The apparent accumulative loss in capacity on cycling of Na/S cells is explained in terms of increasing polarization which, in turn, is related to the steel corrosion phenomenon.