Pulsed-current charging of lead/acid batteries — a possible means for overcoming premature capacity loss?

A pulsed-current technique is evaluated for the rapid charging of lead/acid cells that are prepared with either low-antimony or lead-calcium-tin grids. For comparative purposes, these cells are subjected to repetitive reserve-capacity cycling under either pulsed-current or conventional, invariant-current recharge. Although the latter charging is recommended by the manufacturers of the respective grids, it invokes premature capacity loss when combined with the high-rate discharge of the reserve-capacity test. Two significant benefits are found with the pulsed-current technique, namely, a reduction in recharging time by an order of magnitude (i.e., from 10 to 1 h), and an increase in cycle life by a factor of three to four. Temperature effects play only a minor role in prolonging battery endurance under pulsed-charging conditions. The technique also has the ability to recover the capacity of cycled cells. As expected, premature capacity loss occurs in both Pb---Sb and Pb---Ca---Sn cells cycled under invariant-current charging. The phenomenon is more acute in Pb---Ca-based cells. The decline in capacity of Pb---Sb cells is associated with a progressive change in the nature of the positive active material, i.e., from low crystallinity in the precursor material to a more defined crystallinity in the cycled mass. This behaviour reduces both the available surface area and the reactivity of the active material with the battery acid. By contrast, the capacity loss in Pb---Ca---Sn cells is related to both a progressive increase in the crystallization of the active material during cycling (i.e., development of small crystals) and to the growth of a resistive ‘PbO’ layer immediately adjacent to the grid member. The latter phenomenon is the more dominant. Pulsed-current charging is found to be an effective means for delaying the crystallization process in the active material, as well as for minimizing the development of the ‘PbO’ layer during cycling. Thus, pulsed charging offers a promising approach towards enhancing the cycle life of Pb---Sb and — more importantly — Pb---Ca---Sn cells, particularly under rapid-recharge conditions.