PULSED-CURRENT FORMATION OF TETRABASIC LEAD SULFATE IN CURED LEAD-ACID-BATTERY PLATES

The formation of cured lead/acid battery plates containing a high level (65 wt.%) of tetrabasic lead sulfate (4BS) has been evaluated under both invariant- and pulsed-current conditions. Prior to formation, the plates are subjected to either a short or a long soaking period. The mechanism of formation is dependent on the duration of this treatment. After a short soaking time (30 min), the 4BS is converted to PbO2 via PbSO4. By contrast, after a long soaking period (15 h), oxidation of 4BS and PbSO4 can proceed simultaneously and produce a high incidence of large voids within the resulting PbO2 agglomerates. Each of these two mechanisms is unaffected by the waveform of the applied current. Nevertheless, there is a noticeable change in the morphology of the PbO2 itself. Anhedral particles are produced under invariant-current conditions, whilst well-defined acicular crystals are obtained with pulsed current, particularly at low duty cycles. Irrespective of the soaking period and the corresponding formation mechanism, pulsed current is more efficient in oxidizing 4BS to PbO2.