Formation of Positive Lead—Acid Battery Plates

Formation of Positive Lead—Acid Battery Plates 445... 

B.K. Mahato and W.C. Delaney, Formation efficiency of positive plates of a lead-acid battery, US Patent 4 656 706, assigned to Globe-Union, Inc. (Milwaukee, WI), April 14,1987. 

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. 

Glass fibres coated with Sn02 have been developed and used in lead-acid battery positive plates with the aim to improve the process of plate formation and the performance of the plate. 

Selection of a particular method for the production of 4BS pastes depends on the type of battery application, the time of plate formation and the planned service life of the battery. 4BS pastes are gaining an ever-increasing share in the production of positive plates for lead-acid batteries. 

One conductive additive which is relatively stable is barium plumbate (BaPbOs) [11]. This is a ceramic [12] with the perovskite structure and is easily made by standard ceramic-powder technology. Addition of this material to positive plates in a lead-acid battery significantly improves the formation efficiency. The formation mechanism is changed when the conductive particles are dispersed in the plate. Formation not only proceeds from the grid towards the centre of the pellet, but also takes place slowly around the conductive particles in the plate. The conductive paths of Pb02 grow and make connection with each other during formation to establish a network, which further facilitates the formation. 

Chemical and Electrochemical Reactions during Formation of Lead—Acid Battery Positive Plates... 

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. 

D. Pavlov, Mechanism of the Processes of Formation of Lead-Acid Batteries Positive and Negative Plates, in Proc. Symp. on Batteries for Traction and Propulsion, 1972, Columbus Section of the Electrochemical Society, 135. 

Unfortunately, the lead (II) compounds are not very conductive. Lead sulfate is an insulator and the lead oxides and basic lead sulfates are semiconductors. Before they are given the first charge, ealled formation , battery plates are composed of mixtures of these materials. Plate formation eannot proceed until a conductive pathway is formed. Pavlov and co-workers [10] have shown that in acid solutions, the materials next to the current-collector are first eonverted to conductive lead and lead dioxide. Formation then proeeeds inward towards the centre of the pellet (see Chapter 3). Lead sulfate is the last material to be eonverted in the formation process. The rate of formation is thus limited by the non-conductive nature of lead oxide, especially in the positive plate. 

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