The mechanism of expander action is reviewed, with special emphasis on the role of its organic constituent and the method by which this constituent is derived from lignin. An alternative material, SYNTAN BNF, is proposed for application as the organic constituent. BNF also increases the overvoltage for gas evolution, which could be of special interest for valve-regulatedlead/acid batteries. BNF is compatible with ~-oxi-naphtholic acid (AONA), an inhibitor of lead oxidation. | ELSEVIER Journal of Power Sources 59 1996 25-30 A view on chemically synthesized expanders for lead acid battery negative plates . Aidman Teledyne Continental Motors Battery Products Operation Redlands CA 92 375. USA Received 30 October 1995 accepted 13 November 1995 Abstract The mechanism of expander action is reviewed with special emphasis on the role of its organic constituent and the method by which this constituent is derived from lignin. An alternative material SYNTAN BNF is proposed for application as the organic constituent. BNF also increases the overvoltage for gas evolution which could be of special interest for valve-regulated lead acid batteries. BNF is compatible with cr-oxi-naphtholic acid AONA an inhibitor of lead oxidation. Keywords Lead acid batteries Negative plates Expanders SYNTAN BNF 1. Background to expander action The active mass of the spongy negative electrode can lose its operational ability relatively quickly particularly at low temperatures high-rate discharges and high acid concentrations. This decline in performance is attributed to passivation of the electrode and to recrystallization and shrinkage of the spongy lead. During anodic polarization discharge the surface of the negative electrode is covered uniformly by a layer of lead sulfate. The latter has a very limited solubility in dilute sulfuric acid . X 10 M PbSO4 1 . As a result a supersaturated solution is formed near the electrode surface. The lead sulfate passivates the spongy lead and hinders the anodic charging process of the electrode. Lead sulfate deposits as a tight and impenetrable film that results in sintering of the negative active-material and thereby causes a reduction in the volume of the mass. The change in capacity by sintering occurs faster than the change in the true surface area for example a tenfold decrease in the first parameter is accompanied by only a fivefold decrease in the second 2 . From measurements of double-layer capacitance it has been
