Effect of Mechanical Milling and Addition of Sb on the Crystal Structure and Discharging Properties of Positive Active Material PbO_2 in Lead-Acid Battery

PbO2 powders, which are the positive active materials in the lead-acid battery, were mechanically milled with Sb2O3 powders. It is well known that Sb contained in the grid of lead-acid battery is useful for the protection of the premature capacity loss. Before milling, most of PbO2 powders consist of tetragonal β-phase, but in the progress of milling process, they were transformed to orthorhombic α-phase. The intensity of X-ray diffraction peaks of Sb2O3 decreases with increasing milling time, and after the milling of 5 hours, they almost disappear, which indicates that the alloying between PbO2 and Sb2O3 proceeds during milling process. The intensity of the reduction peak in the cyclic voltammetry (CV) curve of the electrode constructed from the PbO2 powders is larger than that of the electrode constructed from PbO2 powders added with Sb2O3. The discharge capacity of the electrode constructed from PbO2 powders increases with increasing milling time, but that of the electrode constructed from PbO2 powders added with Sb2O3 is rather reduced. The difference of the properties between these two electrodes may be ascribed to the difference of the microscopic structure of PbSO4 particles, which are formed during the discharging process.