Positive plate changes

The changes in PbO and PbS04 content in the paste (determined by wet analysis) during soaking of the positive plates are presented in Fig. 3.5. Similar changes in chemical composition have also been observed with the negative plates. After 8 h, the amount of PbS04 in the positive paste increases by 22,47, and 60% for acid solutions of 1.05, 1.15, and 1.25 rel. dens., respectively. 

Fig. 3.5. Changes in chemical composition of cured positive plates during soaking in 1.05, 1.15, or 1.25 rel. dens. H2SO4 [6].

Fig. 3.33. (a), (b) Phase composition of pastes prepared with different amounts of acid at 30 and 80°C (c), (d) Changes in C20 capacity of 12-V/42-Ah automotive batteries with positive plates produced from 3BS, 4BS, and IBS pastes (depending on acid strength and preparation temperature) on cycling at 50% DoD. The battery capacity is limited by the positive plates [34]. 

One conductive additive which is relatively stable is barium plumbate (BaPbOs) [11]. This is a ceramic [12] with the perovskite structure and is easily made by standard ceramic-powder technology. Addition of this material to positive plates in a lead-acid battery significantly improves the formation efficiency. The formation mechanism is changed when the conductive particles are dispersed in the plate. Formation not only proceeds from the grid towards the centre of the pellet, but also takes place slowly around the conductive particles in the plate. The conductive paths of Pb02 grow and make connection with each other during formation to establish a network, which further facilitates the formation. 

Once a cell is described, we can measure its potential and decide once and for aU which electrode is the positive electrode (positive plate) and which is the negative electrode (negative plate). Nothing that happens later will change that. 

The reactions that proceed during positive-plate formation have been identified by the accompanying changes in phase and chemical composition of die plates, as well as by the changes in bofli open-circuit and charge potentials of the plates. The phase composition is determined by X-ray diffraction analysis (XRD) and the chemical composition through conventional analytical methods the potentials are measured vs. a Hg Hg2S04 reference electrode. 

For vertically arranged surfaces (see Fig. VII.3 a), as the angle a varies from 0 to 90 (i.e., as the position of the plate changes from perpendicular to parallel relative to the flow axis), the proportion of particles of diameter 5 and 10 /x remaining increases, while that of particles 30, 40, and 50 /x in diameter falls. 

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