Lead acid

The lead acid battery has been in use for well over a century but practical batteries began as early as1860 invented by Raymond Gaston Plante. His fabrication method consisted of 2 long strips of lead foil sandwiched between layers of coarse cloth that were spirally wound and immersed in a bath of 10% sulfuric acid. These early batteries had very little capacity as the surface area and amount of lead was limited. Interestingly the capacity of these early cells increased as the batteries were cycled as corrosion of the substrate foils created more active material and increased surface area.

The major use of present day lead acid cells is as storage batteries for vehicles where they primarily act to provide starting power for the internal combustion engine. Most vehicles use a 12 volt battery with a typical capacity of 40 to 60 Ah. This type battery weighs about 14.5 kg and will deliver 450 to 800 amps which is easily sufficient to start a vehicle form a cold start. In a modern lead battery approximately 60% of the battery weight is lead. Its production continues to grow as new battery applications such as energy storage, emergency power and electric and hybrid vehicles emerge. A lead acid battery system is used almost extensively in telephone systems, power tools, emergency lighting and as power sources for the mining and material handling industries. It is almost always the least expensive battery solution for any application but not necessarily the best matched to the application requirements. Electric vehicle applications typically require batteries that can provide 100 to 300 volts to their systems. The lead acid battery has a high electrical turn around efficiency, 75 to 80% which makes it attractive for electrical vehicle use. The world’s largest energy storage battery system located in Chino California was brought online in 1988. The system consists of individual industrial off the shelf lead acid batteries wired in series and parallel providing 40 MWh’s of potential backup power capable of delivering 10 MW into the utility grid at 2000 volts and 8000 Amps. Listed among the batteries advantages is its low cost, easy availability, moderately good temperature range performance, high electrical efficiency, high cell voltage ( >2.0 v which is the highest of all aqueous-electrolyte cells.), and good charge retention. As for disadvantages it has a relatively low cycle life (50 to 500 cycles, limited energy density ( 30 to 40 Wh/kg) and it is difficult to manufacture in small sizes.


The overall balanced chemical reaction of this cell is :


              Pb + PbO2 + 2H2SO4 = 2PbSO4 + 2H20


From left to right the reaction is discharging electrons while right to left it is charging. As the cell discharges both the positive and negative electrodes are reduced to lead sulfate as shown below. The process reverses on charging.


     Negative electrode                     Pb = Pb2+ + 2e


                                                   Pb2+ + SO42-  = PbSO4  


In general the negative electrode is responsible for controlling the cold start characteristic of the cell.


     Positive electrode                 PbO2 + 4H+  + 2e   =   Pb2+  + 2H20  


                                                   Pb2+ + SO42-  = PbSO4

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