MODELING OF CYLINDRICAL ALKALINE CELLS .6. VARIABLE DISCHARGE CONDITIONS

A one-dimensional constant current model of Zn-MnO2 alkaline cells is extended to simulate other modes of discharge. The model predicts the cell performance under constant load, power, and pulsed current. A pseudo-steady current has been assumed to represent the changing discharge rate for the constant load and power cases. At an equivalent initial discharge rate and zero cutoff voltage, the constant load discharge results in the highest cell capacity and the constant power discharge the lowest, due primarily to cathodic overpotential differences. During pulsed current discharge the cell capacity is increased as more uniform species concentrations are created during the relaxation period, when the external current drain is zero. The model predicts that a decrease in duty cycle will improve the cell capacity, which is confirmed by experimental data. Also, an increase in frequency raises the usable cell capacity up to a certain limit. Further increase in frequency beyond this point has no improvements to the cell capacity since the species concentrations are essentially uniform throughout the cell. The model has also been used to slow that the sensitivity of the initial concentration of hydroxyl ion on cell performance can be reduced significantly when the cell is operated under pulsed current discharge.