AC impedance and state-of-charge analysis of alkaline zinc/manganese dioxide primary cells

Alternating current impedance data of alkaline $Zn/MnO_2$ cells were analysed in view of identification of suitable parameters, which depend on the state-of-charge (SOC) of the cells. The impedance of a slightly discharged cell was found to possess impedance considerably lesser than that of an undischarged cell. The data in the form of Nyquist plot contained an inductance part at very high frequencies, a capacitive semicircle at high frequencies and a diffusion linear spike at low frequencies. The low frequency linear spike gradually transformed into a capacitive semicircle with the decrease of SOC of the cell, which was attributed to the nature of the reactions at the Zn anode. Of several impedance parameters that were examined, equivalent series capacitance $(C_s)$ was found to have a strong dependence on SOC of the alkaline $Zn/MnO_2$ cells. There was a continuous change in a partially discharged cell during its ageing, which was reflected by transformation of low frequency data into a clear semicircle