Clarification of phase morphologies of alpha and beta lead dioxide for positive electrode applications

This study focused on to the morphology of positive active mass, PbO2, polymorphs (orthorhombic α-PbO2 and tetragonal β-PbO2) used in the lead acid battery technology. In order to better understand the thermodynamics of the system, new E-pH diagrams are drawn as a function of temperature as well as pH and acid concentration. The macro/micro morphology and the phase composition of the positive electrode active mass structure were investigated by means of scanning electron microscope, transmission electron microscope and x-ray diffraction analysis. The results indicate that, both the formation acid concentration and the current-time profile effects the morphology and the phase composition, namely α-/β- ratio, of the active mass. In high acid concentration, production of α-PbO2 greatly inhibited. In contrast, the PbO2 formation rate is high, however, the total amount of PbO2 formed is limited. In the light of this information, a model has been proposed here to explain the effect of acid concentrations on the positive active mass characteristics. Morphological investigations revealed that the needle like and spherical PbO2 particles are dominant for the high and low formation acid concentrations, respectively. Transmission electron microscopy analysis showed that the β-PbO2 can be in both needle like and spherical morphology. Most interestingly, phase transformation from β-PbO2 to α-PbO2 was observed during transmission electron microscopy analysis. Morphology of these particles that underwent a phase transformation changed as well.