Radiochemistry Studies of Zinc/Nickel Oxide Cells

The zinc/nickel oxide battery system is presently being investigated for future electric vehicle related applications that require good energy storage and high power characteristics. For these applications, however, this battery system is somewhat hindered by the loss of performance on deep discharge cycling due to a gradual migration of the zinc active material. To investigate why, where, and to what extent the zinc migrates during cycling, radiotracer techniques were developed and used to measure electrolyte movement and zinc migration in situ without disturbing the operation of the cell. This novel application of radiotracers to the study of the zinc/nickel oxide battery system has provided new and unique information. The findings indicate that electrolyte movement by forced convection in an operating cell overwhelms electrolyte movement due to natural convection processes, and that this movement is radially outward and inward from the center of the electrode pack during charge and discharge, respectively. The radiotracer zinc studies indicated that zinc migration at the top of the electrode pack is five times higher than at the center of the electrode pack. Autoradiograms of the electrodes before and after cycling confirmed earlier studies that zinc migrates to the nickel electrodes, and, in addition, showed that this zinc transfer is directly from the zinc electrodes through the separators to the nickel electrodes. The amount of zinc transferred depends upon the operating history of the cell and the location within the electrode pack. These results will help direct future development work to enhance the life and performance of deep discharge zinc/nickel oxide battery systems.