The importance of the equilibrium zincate ion concentration in modeling a cylindrical alkaline cell

A mathematical model of the Zn/MnO2 cylindrical alkaline cell is revised by using a more appropriate expression for the equilibrium zincate ion concentration. The new expression models the equilibrium behavior of solid zinc oxide in alkaline electrolyte, whereas the previous expression models the solid zinc dihydroxide equilibrium. The new expression results in the prediction of lower and more uniform zincate ion concentration profiles. The influence of the equilibrium zincate ion concentration is analyzed through the precipitation rate of zinc oxide. The zincate ion concentration profiles for the revised case are responsible for the simulated improvement in cell performance. Adverse cell voltage fluctuations near the end of discharging are determined to be caused by a localized region where the zincate ion concentration is zero. These fluctuations are considered numerical discrepancies and are net physically realistic. Numerical remedies that successfully remove the cell voltage fluctuations are provided, but they are employed by weakening the assumption of concentrated ternary electrolyte theory. (C) 1999 Elsevier Science S.A. All rights reserved.