Lead-acid battery active materials

This chapter reviews the effects of additives in the positive active-material of the lead acid battery. Common materials found in the oxide and the positive-plate paste, such as lead oxides, basie lead sulfates, and lead earbonate, are not included. Additives and impurities that derive from grid eorrosion or from the reaction of the plate with the electrolyte are also beyond the seope of this chapter. 

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 tubular positive plate uses rigid, porous fiber glass tubes covered with a perforated plastic foil as the active material retainer (Fig. 2). Dry lead oxide, PbO, and red lead, Pb O, are typically shaken into the tubes which are threaded over the grid spines. The open end is then sealed by a polyethylene bar. Patents describe a procedure for making a type of tube for the tubular positive plate (90) and a method for filling tubular plates of lead—acid batteries (91). Tubular positive plates are pickled by soaking in a sulfate solution and are then cured. Some proceed directiy to formation and do not requite the curing procedure. 

Sulfuric Acid. Sulfuric acid is a primary active material of the battery. It must be present to provide sufficient sulfate ions during discharge and to retain suitable conductivity. Lead—acid batteries generally use an aqueous solution of acid in either a free-flowing or in an immobilized state. 

Pb02 as Active Material in Lead-Acid Batteries... 

Table 5. Surface areas of the active materials in lead-acid batteries...

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 plate support in lead-acid batteries is usually called the "grid". In most batteries the grid has to provide both mechanical support for the active material and electronic conductivity for the collected current. 

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. 

Practically every battery system uses carbon in one form or another. The purity, morphology and physical form are very important factors in its effective use in all these applications. Its use in lithium-ion batteries (Li-Ion), fuel cells and other battery systems has been reviewed previously [1 -8]. Two recent applications in alkaline cells and Li-Ion cells will be discussed in more detail. Table 1 contains a partial listing of the use of carbon materials in batteries that stretch across a wide spectrum of battery technologies and materials. Materials stretch from bituminous materials used to seal carbon-zinc and lead acid batteries to synthetic graphites used as active materials in lithium ion cells. 

Fig. 5.4 Typical lead-acid battery grid this acts as a framework to hold the active material in place...

Most battery systems employ carbon materials in one form or another, as noted in Table 10.1. The use of carbon materials in batteries stretches across a wide spectrum of battery technologies. The variety of carbon runs the gamut from bituminous materials, used to seal carbon-zinc and carbon black powders in lead acid batteries, to high performance synthetic graphites, used as active materials in lithium-ion cells. The largest use is as a conductive diluent to enhance the performance of cathode materials. In many instances, it is used as a conductive diluent for poorly conducting cathode materials where carbon blacks, such as acetylene black, are preferred. It is essential that... 

Current collector for advanced lead acid batteries Graphite used as conductive diluent in the cathode Conductive diluent in the cathode Anode-active material component... 

Calculate the theoretical energy density of a lead-acid battery at 25 °C. Assume that 1 mol each of lead and lead dioxide is discharged from an initial H2S04 concentration to final acid concentration. The 54 A hr are produced at room temperature in this discharge at an average voltage of 2 V. Base your calculations only on moles of the three active materials, i.e., lead, lead dioxide, and sulfuric acid. (Bhardwaj)... 

Current collector — In the battery discipline, a good electron conductor support designed to transfer electrons from the external circuit to the active materials of the cell. Current collectors are usually metal foils or nets that are inert under the operational chemical and electrochemical conditions. In some cases carbon cloth is also used. In secondary - lead-acid batteries the chemical nature of the current collectors (plates, grids) is particularly imperative, as it influences the self-discharge and the performance under overcharge and discharge conditions. Frequently, current collectors have also the important role of imparting mechanical stability to the electrodes. 

Costs of the active materials and, in the case of D/A-systems, of the solvent/ electrolyte system, are for any practical case extremely important, for they are proportional to the charge to be stored. Cost aspects in batteries are comprehensively treated in [477]. The specific cost per Ah is reduced at high cycle numbers. Thus good cyclability is important, too. Graphite, H2SO4, or, with some restrictions, carbon blacks and carlmnaceous materials are inexpensive materials. PANI is an inexpensive ICP, but this does not generally apply for all other ICPs as erroneously stated in the literature [562, 563]. The pure material costs for a lead-acid battery are below 4 DM/ kWh. But it is nearly impossible to meet this cost level in the case of a polyacetylene battery, for the polymer should then be as cheap as < 0.3 DM/kg. 

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