VISUAL OBSERVATIONS OF EARLY SHAPE CHANGES IN A ZINC NICKEL-OXIDE CELL

Visual observations of the back side of a Zn electrode in a Zn/NiOOH single cell indicate that the patterns of Zn formed during charge, and the patterns of ZnO formed during discharge, are both very reproducible. Comparison of these patterns after various early cycles shows identical shapes, indicating that these patterns are established during the initial formation. Potential oscillations of the Zn electrode, during the middle of the charge period, indicate that the electrode oscillates between the Zn- and the ZnO dominating states. It is proposed that the formation, which is obtained at very low current density is at least partially responsible for nonuniform distributions of Zn and ZnO, which are then maintained throughout the cycling of the cell. It is suggested to investigate the effect of the formation procedure on the shape change of the Zn electrode. It is quite possible that a fast initial formation step might improve the uniformity of the Zn electrode and its shape change later on during cycling.