Heat treatment of α- and β-battery lead dioxide and its relationship to capacity loss

It is well known that lead dioxide contains, what has been called, ‘structural water’. Present in the form of OH− ions replacing O2− ions in the anionic sublattice, the ‘structurally bonded’ water can be removed by heating, in the temperature range from 150 to 250 °C. In the present study, the discharge capacities of fresh and heat-treated (140 and 230 °C, respectively) α- and β-PbO2 samples were evaluated in H2SO4 solution of 1.28 g cm−3 sp. gr. at different current densities of 5 to 40 mA cm−2. It was found that the capacity decreased when structural water was removed. This loss of capacity is important when α-PbO2 samples are considered. The energy of dehydroxilation was deduced by applying kinetic considerations to thermograms, obtained experimentally. The removal of the OH− groups from β-PbO2 needs an energy twice that of the α-form.