Thermal Decomposition Mechanism of Formed and Cycled Lead Dioxide Electrodes and Its Relationship to Capacity Loss and Battery Failure

Abstract

The structural changes accompanying capacity loss in the PbO 2 / PbSO 4 electrode were followed using differential thermal analysis. The thermal decomposition mechanism of formed plates was found to differ, depending on the method of manufacture. All cycled plates, however, gave the same decomposition mechanism after a few cycles. The major changes in the DTA curves, as the positive electrode was cycled to failure, was the gradual disappearance of the exothermic peak at 200°C and the endothermic peak at 358°C. It is believed that these peaks are associated with an electrochemically active amorphous form of PbO 2 . As the electrochemically active PbO 2 is cycled to failure it is converted to an electrochemically inactive form of PbO 2 . This latter form of PbO 2 gives DTA results similar to those obtained on reagent PbO 2 . The continual conversion of electrochemically active PbO 2 to the electrochemically inactive PbO 2 is one of the major factors that accounts for the loss in battery capacity and ultimate failure.