Lead-acid batteries negative electrodes

Some battery designs have a one-way valve for pressure rehef and operate on an oxygen cycle. In these systems the oxygen gas formed at the positive electrode is transported to the negative electrode where it reacts to reform water. Hydrogen evolution at the negative electrode is normally suppressed by this reaction. The extent to which this process occurs in these valve regulated lead —acid batteries is called the recombination-efficiency. These processes are reviewed in the Hterature (50—52). 

In the lead-acid battery, sulfuric acid has to be considered as an additional component of the charge-discharge reactions. Its equilibrium constant influences the solubility of Pb2+ and so the potential of the positive and negative electrodes. Furthermore, basic sulfates exist as intermediate products in the pH range where Fig. 1 shows only PbO (cf. corresponding Pour-baix diagrams in Ref. [5], p. 37, or in Ref. [11] the latter is cited in Ref. [8]). Table 2 shows the various compounds. 

Although the rate of these reactions is slow, according to its thermodynamic situation the lead dioxide electrode is not stable. Since a similar situation applies to the negative electrode, the lead-acid battery system as a whole is unstable and a certain rate of water decomposition cannot be avoided. 

Micka K., Rousar I. Theory of Porous Electrodes. XII. The Negative Plate of the Lead-Acid Battery. Electrochim. Acta. 1974 19 499-502. 

The characteristic of the lead-acid battery is that both electrodes are based on the chemistry of lead. The discharge-charge process is known as the double sulfate reaction, with the positive and negative electrodes being the seats of a dissolving-precipitating (and not some kind of solid-state ion transport or film formation) mechanism of the lead sulfate. The cell, the electrode reactions and the cell reaction are ... 

The anode, cathode, and overall cell reactions during discharge of a lead-acid battery are Anode (negative electrode) Pb + SO/ -> PbS04 + 2e (26.170)... 

Whilst the influence of impurities and additives on charge or float conditions is common to all types of lead-acid batteries, with VRLA batteries there is the additional concern of self-discharge of the negative by reduction of the oxygen generated at the positive electrode, i.e.,... 

The lead-acid battery has high-surface area Pb as a negative electrode and Pb02 as a positive. In the concentrated (37%) H2SO4 electrolyte solution, the reactions occurring at the electrodes lead to the overall process ... 

The chemistry of these batteries is that of conventional lead-acid batteries. However, they have a unique characteristics. The oxygen generated on overcharge is recombined in the cell and there is no water loss. Indeed, oxygen reacts at the negative electrode ... 

Figure 9 0 Components of a lead acid battery, (a) Cast lead alloy grid, (b) separator, (c) positive electrode, (d) negative plate, (e) negative plate group, (f) positive plate group, (g) plate block with separator, and (h) the complete battery. (Reproduced with permission from Ref. [25], 1985, Wiley-VCH.)...

In floating mode, it is better to use VRLA (Valve Regulated Lead Acid) batteries where the reactions are water oxidation at the positive electrode and dioxygen reduction at the negative electrode. When a steady state is reached in an ideal VRLA battery, there is no mass consumption, which is not the case fora vented battery for which the floating mode leads to a continuous loss of water. 

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