Lead-acid batteries positive electrodes

In fabricating a lead-acid battery positive electrode, using more sulfuric acid in the positive paste can improve the battery capacity. This is because more sulfuric acid can increase the quantity of lead sulfate in the positive paste, leading to more production of P-Pb02 due to the oxidation of lead sulfate in the formation process. The additional benefit is that the plate porosity can be increased with increasing lead sulfate in the paste. The increased lead sulfate can go into the internal active materials, improving the use ratio of lead dioxide. 

The mercurous sulfate [7783-36-OJ, Hg2S04, mercury reference electrode, (Pt)H2 H2S04(y ) Hg2S04(Hg), is used to accurately measure the half-ceU potentials of the lead—acid battery. The standard potential of the mercury reference electrode is 0.6125 V (14). The potentials of the lead dioxide, lead sulfate, and mercurous sulfate, mercury electrodes versus a hydrogen electrode have been measured (24,25). These data may be used to calculate accurate half-ceU potentials for the lead dioxide, lead sulfate positive electrode from temperatures of 0 to 55°C and acid concentrations of from 0.1 to Sm. 

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. 

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 ... 

All equilibrium potentials are referred to a standard hydrogen electrode. The Hg Hg2S04 electrode is widely used in lead-acid battery investigations. This electrode has a potential which is 0.620 V more positive than that of the standard hydrogen electrode at pH = 0 [18]. 

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 ... 

It has been found that H3PO4 prevents capacity decay of the positive electrode during cycling of gelled lead—acid batteries for electric vehicle applications [21]. Addition of phosphoric acid to VRLAB electrolyte yields stable capacity performance of these batteries in different solar power systems [37]. 

The electrode system Pb Pb02 PbS04 HH2OIO2 forms on the positive plates of lead—acid batteries on open circuit stay and this electrode system has a stationary potential close in value... 

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 a nearly fully recharged lead acid battery, two half-reactions are In competition at the positive electrode... 

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. 

The lead-acid battery, which is used mainly in cars, was invented by Gaston Plante in 1859. It contains a liquid electrolyte which is a aqueous sulfuric acid solution with density 1.290 g/cm (about 4.5M H2SO4 in concentration). The electrodes are two lead rods or plates that have each rmdergone a special treatment. The negative electrode consists of a lead plate covered with spongy lead. The positive electrode consists of lead(II) oxide deposited on the lead rod or plate. Each cell provides a 2 V output, so six cells in series give a 12 V battery. 

In some cases, the electrode reaches some potential value at which an electrochemical dissolution of its components into the electrolyte occurs for example, the positive grid of lead-acid batteries contains antimony at the high potential of the grid, Sb can be oxidized to soluble SbO which can be reduced at the negative lead electrode. An antimony deposit then occurs leading to an acceleration of the self-discharge corrosion reaction. 

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