Cobalt Segregation in Nickel Electrodes during Nickel Hydrogen Cell Storage

Abstract

Storage of nickel electrodes in a hydrogen environment can result in significant changes in the performance of these electrodes in nickel hydrogen battery cells. Such performance changes appear to be associated with the formation of cobalt oxides from the cobalt additives incorporated in the active materials of the nickel electrode. In this study the microscopic location of these cobalt oxides has been mapped using scanning electron microscopy. The cobalt additive in the active material was found to be depleted around the nickel metal particles comprising the sintered current‐collector matrix. The cobalt‐containing oxides found in chemical analyses of these electrodes were re‐deposited in areas several microns or more distant from the sinter particles. A mechanism is proposed for cobalt segregation in nickel electrodes that involves the reaction of the active material with hydrogen gas at low potentials to initiate the segregation process, which then proceeds through a dicobaltite ionic intermediate when the potential of the cell is eventually brought back to its normal operating level.