Bruce S. Dunn

In situ evaluation of container corrosion in sodium- sulphur batteries

Recent improvements in container materials for Na/S cells (central sodium type) have led to greatly enhanced cell life and performance. Although problems with rapidly decreasing capacity are no longer observed, cells appear to exhibit a slowly increasing resistance with time. This paper describes anin situ technique for assessing the electrical stability of various container materials and determining the extent that corrosion processes influence cell resistance changes. Potentials within the sulphur electrodes of operating cells were measured over prolonged cycling times. Results indicate that chromized steel possesses excellent electrical stability compared to 347 stainless steel and that container corrosion accounts for only a fraction of the increase in total cell resistance.

Interfacial behaviour of various liquid electrode/β″-alumina systems

Three different liquid electrode/sodiumβ″-alumina interfaces were investigated. The NaNO3/β″-alumina interface displays ohmic behaviour although the resistance is somewhat larger than expected. The sodium/β″-alumina interface exhibits asymmetric resistance with respect to d.c. current flow. Cyclic voltammetry results suggest that a Na2O film is being modified electrochemically during the sweeps. When a sodium amalgam electrode is utilized, the film, if it is present, has very little effect. The asymmetric resistance is not observed and there is good agreement between d.c. and a.c. resistances after only a small amount of sodium deposition.