Ageing of magnesium/manganese dioxide primary cells

Mg/MnO2 primary cells which were more than a decade old were investigated for their discharge capacity, a.c. impedance behaviour, delay time, effect of added water into the cell and effect of temperature. Although the cells were aged for a long duration, they were electrochemically active and yielded good discharge capacity, thus suggesting an extraordinary long shelf-life. There was a marginal increase in cell capacity subsequent to injection of 2 ml of water into a CD-size Mg/ MnO2 cell. The a.c. impedance of a partially discharged cell included the contributions of surface passive film on the Mg anode and corrosion of the Mg metal. The internal resistance of the cell was found to increase with storage time, suggesting that the resistance of a fresh cell also could similarly increase. By increasing the cell temperature, the impedance decreased considerably and also the delay time. These results suggested that the increase of temperature had favourable effects on the performance of the aged Mg/MnO2 cells.