Chapter 5 - Negative Plates in Valve-regulated Lead-Acid Batteries

Abstract

This chapter discusses the effects of negative plates in valve-regulated lead–acid (VRLA) batteries. Conventionally, negative plates in lead–acid batteries contain a combination of carbon black, barium sulfate, and an organic additive, which is usually a wood extract. These additives are collectively called an “expander,” although this term is often used purely for the organic component of the mix. The presence of the expander helps to maintain a porous lead structure with a high surface-area during cycling. The three components are usually premixed by the supplier and the composition varies according to requirements. The effects of carbon addition to negative pastes reveals that carbon functions primarily as a conductor, and thereby enhances formation efficiency and reduces the level of residual sulfate. Barium sulfate functions as a nucleation centre for the precipitation of the discharge product and favourably restricts its crystal size. Under conditions where oxygen recombination operates efficiently, battery cycle-life may be reduced if the balance of the charge input and the self-discharge at the negative plate does not allow the potential of the negative plate to reach a sufficiently negative value during charge. The self-discharge rate can be reduced by improving purity standards.