The elementary physicochemical processes during the first stage of formation of the negative lead-acid battery plate

Abstract

During the first formation stage of the negative plate in H 2SO 4 solution lead monoxide and tribasic sulphate transform into Pb and PbSO 4 giving rise to a Pb−PbSO 4 zone. It was established that these processes take place within a thin layer (the δ-layer) situated between the Pb−PbSO 4 zone and the paste. The rate determining step is the transport (by diffusion and migration) of H + and SO 4 2− ions from the bulk of the electrolyte towards the δ-layer. An equation is derived for the dependence of the concentration of the H 2SO 4 in the Pb−PbSO 4 zone on the thickness of this zone. It was found that during formation until a limiting thickness of the Pb−PbSO 4 zone, PbSO 4 originates mainly at the expense of the H 2SO 4 present in the bulk of the electrolyte. When the formation rate of PbSO 4 becomes very small the reaction of PbSO 4 reduction to Pb takes place. This reaction proceeds in a second reaction layer (the α-layer) which is located in the Pb−PbSO 4 zone at the plate surface. Subsequently, the formation of PbSO 4 in the δ-layer takes place at the expense of H 2SO 4 generated in the α-layer. The model is confirmed by the experimentally determined distribution of PbSO 4 across the cross-section of the plate during formation.