Oxygen Activity and Asymmetric Polarization at the Sodium/Beta"- Alumina Interface

Asymmetric polarization at the sodium/beta"-alumina i terface during ionic charge transfer has been studied using cyclic voltammetry with Na/beta"-alumina/Na cells. It was found that contamination ofthe sodium electrode by oxygen, as 02 or H20, causes asymmetric polarization. Polarization is quite severe in the range of 150~176 and is attributed to the presence of an adsorbed oxide film. The adsorption/desorption behavior of the resistive film could be described by a sim-ple Langmuir model. Asymmetric polarization can be eliminated by lowering the oxide content of the sodium electrode to levels such that adsorption is negligible. This is achieved by the use of carefully dried electrolyte tubes with either electro-lytically generated sodium, or sodium from which the oxygen has been scavenged with Ti sponge. Asymmetr ic harge transfer esistance with dc ionic current flow at the sodium/B'r-alumina interface has been reported by several workers (1-6). Significant asymmet-ric polarization can be harmful to the efficiency of bat-tery operation and is associated with early electrolyte failure. The increasing resistance at the electrode/electrolyt