Zinc Electrode Shape Change in Secondary Cells

Shape change, the reduction in zinc electrode area with cycling, is a limiting factor in the life of most secondary zinc batteries. This investigation was an attempt to elucidate the mechanism of shape change by monitoring the pattern of current and potential distribution over the surface of a zinc electrode during cycling. This was done while keeping all electrode and cell parameters similar to those found in conventional cells. Differences in the secondary current distribution during charge and discharge result in exhaustion of the reducible zinc species at the plate periphery in the early stages of cycling. This generates a concentration cell which corrodes zinc off the plate edge and deposits it in the plate center. Shape change is a result of these concentration cell effects and the transfer of zincate from the plate periphery to the plate center in the early stages of discharge. Many other hitherto unexplained phenomena related to shape change were rationalized on the basis of these findings and mechanism.