Shape change, the redistribution of active material over the zinc electrode surface as a result of cell cycling, is hypothesized to be caused by convective flows driven primarily by membrane pumping. A mathematical model is formulated based on the convective flow hypothesis for the zinc‐silver oxide secondary cell. The numerical solutions predict redistribution of zinc material over the zinc electrode, fluid flow rates, and variations of current distribution and cell potential with the number of cycles. These calculated results can be compared to experimental results. The results suggest that shape change can be eliminated if the convective flow in the zinc electrode compartment parallel to the electrode surface is stopped.
Experimental data on zinc-silver oxide secondary cells were used to evaluate the convective flow hypothesis on the cause of shape change of zinc electrodes. A cell with flooded, vented electrodes designed to allow "normal" convective flow was studied. Zinc electrodes cycled in this cell showed extensive material redistribution in accord with predictions based on the hypothesis. Measured volume average fluid flow rates for this cell were also in agreement 9 with predicted values. Zinc electrodes cycled in a second cell, designed to minimize convective flow in the zinc electrode compartment, showed virtually no active material redistribution.
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