Stability of beta alumina electrolyte in sodium/FeCl/sub 2/ (Zebra) cells

The authors describe how the stability of beta alumina in fully developed Zebra Na/FeCl/sub 2/ cells under long-term cycling has been proven. In the early stages of development of the Na/FeCl/sub 2/ 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 constituents 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.