Negative plate in VRLA batteries

The eoneern over the performance of negative plates in VRLA batteries has resulted in renewed interest in the influence and mechanisms of organic additives and extensive research programmes have been carried out under the auspices of the ALABC. This work has included an assessment of 34 materials, five of which were synthetie organie compounds that were identified to have the potential to act as effective expander components in lead-acid batteries [32]. Preliminary screening tests for stability in acid, impurities and thermal stability, followed by studies of potentiostatic transients, impedance plots, and cyclic voltammograms [33], have... 

Recent studies have provided a better understanding of the behaviour of negative plates in VRLA lead-acid batteries. The major conclusions of this work can be summarized as follows. 

In VRLA batteries, oxygen reaches the negative plates and is reduced to form water. It also oxidizes the expander and thereby produces carbon dioxide. Consequently, the morphology of the secondary Pb crystals is changed and they become dendrite-like, similar to those shown in Fig. 3.57(a). This results in capacity... 

The AGM materials used in VRLA batteries must sustain the required plate-group pressure, must hold the electrolyte in place, and must allow sufficient (but not excessive) transport of oxygen from the positive plate to the negative. Some of the properties of typical all-glass AGM separators are shown above in Table 6.2 [7]. The following important features are noted ... 

D. G. Vella, L.H. Vu, ALABC Project N1.2, Overcoming negative-plate capacity loss in VRLA batteries cycled under partial-state-of-charge duty. Final Report, July 2000 to June 2002, Advanced Lead-Acid Battery Consortium, Research Triangle Park, NC, USA, 2002. 

The total volume of H2SO4 solution in flooded batteries is distributed between the active block , comprising positive and negative plates and separators inbetween, and the electrolyte reservoir above the active block. In VRLA batteries, the whole electrolyte volume is contained in the active block, which is 96% saturated. Within the active block, the electrolyte fills the pores of the plates and separators, and the spaces between the positive and negative... 

For application in VRLA batteries, a special three-layer separator has been developed in this laboratory comprising one thin AGM sheet, which is in contact with the negative plate, one thick AGM sheet that contacts the positive plate and a modified AGM (MAGM) membrane between these two AGM sheets which separates the two electrode spaces [15]. This separator... 

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