The Lead-Acid Battery

The fundamental elements of the lead-acid battery were set in place over 100 years ago. Gaston Plante [2] was the first to report that a useful discharge current could be drawn from a pair of lead plates that had been immersed in sulfuric acid and subjected to a charging current. Later, Camille Faure [3] proposed the concept of 

The discharge reactions of the lead-acid cell are as follows  

Positive plate Pb02 -I- 3H+ - - HSO4 +2e PbS04 -I- 2H2O Negative plate Pb -I- FISO4 PbS04 -I- H -I- le  

Positive-plate expansion. This can occur both in the plane of the plate (if the grid is stretched by a growing corrosion layer) and in the direction normal to the plate (through expansion of the active material itself). Repetitive discharge and 

Acid stratification. On recharge, sulfuric acid is produced in and between the plates and there is a tendency for acid of higher concentration, which has a greater relative density, to collect at the bottom of the cell, see Fig. 1.3 [7]. 

Some Common Types of Secondary Batteries 20.3.3.1 The Lead-Acid Battery 

The best known and most widely used secondary battery is the lead-acid battery, which consists of a lead anode and a lead dioxide cathode in a 25% solution of sulfuric acid. The reaction at the anode during discharge is 

We note that sulfuric acid is being consumed during discharge, and an equivalent amount of water is formed. The resulting decrease in density of the electrolyte used to be the basis for the method used in many garages to test die state of charge of a car battery by measuring the density of the electrolyte. 

6) The real situation is invariably more complex. The screen is not made of pure Pb, but may contain some Ca or Sb. A binding material is used to increase adhesion of the lead particles to the screen. Each manufacturer has his own secret formulations but we do no need to know these to understand how such batteries operate. 

Another common mode of failure of batteries is loss of electrical contact between the active material and the current collector. There are many other ways in which batteries can fail, such as the aging of separators and accidental contact between anode and cathode. These problems are not discussed here. 

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The U.S. primary battery market is divided according to the chemical system used in the batteries, whereas the secondary battery market is usually divided according to usage. The 1989 estimate of the total battery market is given in Table 1. The lead—acid battery accounts for over 85% of the secondary battery market. 

Because the nickel—iron cell system has a low cell voltage and high cost compared to those of the lead—acid battery, lead—acid became the dorninant automotive and industrial battery system except for heavy-duty appHcations. Renewed interest in the nickel—iron and nickel—cadmium systems, for electric vehicles started in the mid-1980s using other cell geometries. 

The lead—acid battery is one of the most successful electrochemical systems and the most successful storage battery developed. In 1988 total battery sales, excluding Eastern European central economy countries, were more than 17 biUion (1). Lead—acid battery sales accounted for about 57% of that figure. About 80% of the lead [7439-92-1] (qv), Pb, consumption in the United States was for batteries in that year. 

The chemical reaction of the lead-acid battery was explained as early as 1882 (11). The double sulfate theory has been confirmed by a number of methods (12—14) as the only reaction consistent with the thermodynamics of the system. The thermodynamics of the lead —acid battery has been reviewed in great detail (15). 

To calculate the open circuit voltage of the lead—acid battery, an accurate value for the standard cell potential, which is consistent with the activity coefficients of sulfuric acid, must also be known. The standard cell potential for the double sulfate reaction is 2.048 V at 25 °C. This value is calculated from the standard electrode potentials for the (Pt)H2 H2S04(yw) PbS04 Pb02(Pt) electrode 1.690 V (14), for the Pb(Hg) PbS04 H2S04(yw) H2(Pt) electrode 0.3526 V (19), and for the Pb Pb2+ Pb(Hg) 0.0057 V (21). 

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. 

Self-Discharge Processes. The shelf life of the lead—acid battery is limited by self-discharge reactions, first reported in 1882 (46), which proceed slowly at room temperature. High temperatures reduce shelf life significantly. The reactions which can occur are well defined (47) and self-discharge rates in lead—acid batteries having immobilized electrolyte (48) and limited acid volumes (49) have been measured. 

The lead—acid battery is comprised of three primary components the element, the container, and the electrolyte. The element consists of positive and negative plates connected in parallel and electrically insulating separators between them. The container is the package which holds the electrochemically active ingredients and houses the external connections or terminals of the battery. The electrolyte, which is the Hquid active material and ionic conductor, is an aqueous solution of sulfuric acid. 

The proper selection of the lead alloy depends on the intended use and the economics of the lead—acid battery appHcation. The metallurgical and electrochemical aspects of the lead are discussed in the Hterature in a comprehensive manner (81,85—87) as are trends of lead alloy use for manufacture of battery grids (88). 

V. M. HalsaU and. R. Pierson, "Plate Processing—The Heart of the Lead—Acid Battery," BCI Proceedings, June 1972. 

Batteries, both primary and secondary, have become very big business indeed, which moreover is growing rapidly. Salkind (1998) in a concise overview of the entire domain of battery types and technologies, estimates that in 1996, the world market in the two types of battery combined totalled ss 33 billion dollars, and that the ratio of secondary to primary battery sales is steadily edging upwards. In spite of its poor charge density per unit mass, the lead-acid battery still accounts for more than a quarter of the total, because it costs so much less than its rivals and lasts well. 

Lead that is incorporated into a lead acid battery is processed to manufacture the battery, and therefore must be counted toward threshold and release determinations. However, the use of the lead acid battery elsewhere in the facility does not have to be counted. Disposal of the battery after its use does not constitute a "release" thus, the battery remains an article. 

Lead-acid batteries remain popular because of their capability to seiwice high and low current demand, produce high voltage, provide capacity up to 100 A-h, and recharge well. Moreover, the lead-acid battery has important material and construction advantages, such as simple fabrication of lead components, the low cost of materials (lead is abundant and much less expen-... 

The history of the lead-acid battery goes back to 1854 when Sinsteden published performance data on this battery system for the first time (cf. Ref., [1]). The practical... 

Lead forms two types of chemical compounds lead (II), and lead (IV) compounds based on Pb24 and Pb4 ions, where those based on Pb2 ions are the more stable. The metal is oxidized even at room temperature to lead oxide (PbO) and also by water that contains oxygen and forms lead hydroxide (Pb(OH),). In the lead-acid battery, the (less stable) lead (IV) oxide (lead dioxide, Pb02), is of greatest importance. Beside these two, a number of oxides are observed in the battery that are mostly mixtures. A brief survey will now be given of those compounds that are of interest for lead-acid batteries. 

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. 

In the lead-acid battery, the reactions at both electrodes include the dissolved state, which means that the reacting species are dissolved in the course of the reaction. The new chemical compounds formed during the reaction are precipitated again as solid matter. This explains the completely different appearance of the material in the charged and discharged states. 

The charge-discharge process can be repeated quite often, since the decisive parameters, solubility and dissolution rate of the various compounds, are well matched in the lead-acid battery system. The chemical conversions occur close to each other, and most of the material transport takes place in the micrometer range. Nevertheless, a gradual disintegration of the active material is observed. 

The lead-acid battery has a peculiarity the electrolyte sulfuric acid not only serves as ion conductor (as charge-transport medium), but it actively participates in the electrochemical reaction ... 

Until about 1880 the lead-acid battery was exclusively then subject of scientific study. Possible commercial utilization lacked suitable charging processes secondary cells had to be charged by means of the primary cells already known at that time. 

Finally, one development results from returning to a basic idea from the dawn of the lead-acid battery, wherein the functions of support for the positive active material and of the separator are combined into one component the gauntlet separator [84] consisting of a coarsely porous, flexible support structure coated with micropo-rous polyethylene material for separation. The future has to show whether this approach will be able to meet all demands. 

One version of the microporous, filled polyethylene separator ( PowerSep ) [113], which is so successful in the lead-acid battery, is also being tested in nickel-cadmium batteries. This separator is manu-... 

It is also useful here to compare the energy stored in the lead-acid battery. A standard 12 V battery may be able to deliver 10 A of current for 4 hr, for a total of 480 W-hr. This amounts to 1632 Btu, which is sufficient to raise 10 lb of catalysts by only 580°F, over the course of four hours. 

What is (a) the electrolyte and (b) the oxidizing agent during discharge in a lead-acid battery (c) Write the reaction that takes place at the cathode during the charging of the lead-acid battery. 

The electrolyte was a solution of ammonium chloride that bathed the electrodes. Like Plante s electrochemistry of the lead-acid battery, Leclanche s electrochemistry survives until now in the form of zinc-carbon dry cells and the use of gelled electrolyte.12 In their original wet form, the Leclanche electrochemistry was neither portable nor practicable to the extent that several modifications were needed to make it practicable. This was achieved by an innovation made by J. A. Thiebaut in 1881, who through encapsulating both zinc cathode and electrolyte in a sealed cup avoided the leakage of the liquid electrolyte. Modern plastics, however, have made Leclanche s chemistry not only usable but also invaluable in some applications. For example, Polaroid s Polar Pulse disposable batteries used in instant film packs use Leclanche chemistry, albeit in a plastic sandwich instead of soup bowls.1... 

Lead is also used in organ pipes, of course. Other uses include the lead-acid battery, radiation shielding, ceramic glazes, and in lead glass. It is a toxic element, and its organic derivatives are also toxic. Tetraethyllead was used for many years as an anti-knock agent in petrol. 

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