Nickel Hydrogen Cell Positive-Electrode Studies: Cobalt Segregation in Reducing Environments

摘要

Nickel electrodes from nickel hydrogen battery cells that had exhibited anomalously low capacities have been tested. Electrode characterization tests showed that changes had occurred in the electrode active material to increase the charge and discharge voltages. The increased charge voltages resulted in a decrease in charge efficiency. These changes apparently resulted from storage of the cell at low voltage with excess hydrogen present in the cell. Chemical and physical analyses indicated that cobalt, a 10% additive in the nickel electrode active material, had undergone segregation from the active material to form a cobalt rich compound that is not normally present in the electrodes. This chemical change is felt to be largely responsible for the changes in electrode performance. A model for the processes causing cobalt segregation is described, and test results are presented to support the model.