Changes in positive lead/acid battery plates during charge/discharge cycling

Active materials and corrosion layers in positive plates of nonantimonial l ead/acid batteries, at different stages of charge/discharge cycling, have b een characterized by using scanning electron microscopy (SEM), X-ray diffra ction (XRD) and X-ray photoelectron spectroscopy (XPS). In the initial stag es of cycling, it has been found that the observed overcharging of cells is responsible for the formation of an underlayer of PbO in the grid corrosio n layer, and this blocks the transfer of charge to the current collecting g rid, causing rapid capacity loss. In the later stages of cycling at a ratio of capacities for charge and discharge (i.e., C/D) of close to unity, the grid corrosion layer does not possess an underlayer of PbO; however, the ac tive material becomes progressively enriched with respect to insulating lea d sulfate. It is suggested that initial overcharging is symbolic of grid co rrosion as the rate of gassing side reactions is kept to a minimum by restr icting the top-of-charge-voltage (TOCV) to 2.55 V, while sulfation of activ e material occurring at C/D values of about unity is probably attributable to stratification of the electrolyte and its concomitant effect on sulfatio n of active material.