Partial State-of-Charge Duty: A Challenge but Not a Show-Stopper for Lead-Acid Batteries!

Abstract

The mechanism by which conventional lead-acid batteries (both flooded and valve-regulated designs) fail when subjected to high-rate partial-state-of-charge (HRPSoC) operation in hybrid electric vehicles is manifested as poor dynamic charge acceptance at the negative plate. This parameter is defined as the amount of charge that is actually delivered to the battery during regenerative braking phases of a driving cycle, divided by the amount of charge that could have been provided by the generator. The possible reasons for this mode of failure are discussed in terms of the processes that support the charge reaction and the competing secondary reactions that can take place at the plate during charge, namely: oxygen reduction (for valve-regulated designs), hydrogen evolution, and the accumulation of capacitive charge. To reach a full understanding of the processes associated with the unusual duty of HRPSoC operation, it is necessary: (i) to examine aspects of the charge reaction that, to date, have received little attention, e.g., local reaction within the pores of the plate active-material, effects of acid concentration on the local solubility of lead sulfate, non-uniformity of potential across the plate; (ii) to evaluate the beneficial effects to be gained from the respective use of carbon, modifications of grid design (twin tab), and the UltraBatteryTM concept.