A lead acid battery consists of a negative electrode made of spongy or porous lead. The lead is porous to facilitate the formation and dissolution of lead. The positive electrode consists of lead oxide. Both electrodes are immersed in a electrolytic solution of sulfuric acid and water.
Battery Application & Technology All lead-acid batteries operate on the same fundamental reactions. As the battery discharges, the active materials in the electrodes (lead dioxide in the positive electrode and sponge lead in the negative electrode) react with sulfuric acid in the electrolyte to form lead sulfate and water.
Voltage of lead acid battery upon charging. The charging reaction converts the lead sulfate at the negative electrode to lead. At the positive terminal the reaction converts the lead to lead oxide. As a by-product of this reaction, hydrogen is evolved.
In the early days of lead acid batteries, the corrosion layers formed on the surface of lead sheet were used as active materials. But at present, the pasted type electrodes, which are made from lead-oxide paste and lead-alloy grid, are used generally.
Electrode potentials and cell voltage for a typical flooded lead–acid battery As charging proceeds, the potentials keep gradually increasing until end of charge is reached. At this point, all lead sulfate is converted to lead on the negative electrode and to lead dioxide on the positive; and the charge is complete.
Meanwhile, the lead-acid-batteries have disadvantages which are the heaviness of battery and the pollution due to toxicity of, since the main materials of lead acid battery are lead and lead alloy after all. Specific energy density of lead acid-batteries is 30–40 Wh/kg, which is only about one-third of Lithium ion batteries.