In this condition, the positive plates are brown in color, and the negative plates are gray. When the battery is discharging (i.e., supplying a current), atoms from the spongy lead on the negative plates combine with sulfate molecules to form lead sulfate and hydrogen.
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.
5.2.1 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.
The negative and positive lead battery plates conduct the energy during charging and discharging. This pasted plate design is the generally accepted benchmark for lead battery plates. Overall battery capacity is increased by adding additional pairs of plates. A pure lead grid structure would not be able to support the above framework vertically.
Such applications include automotive starting lighting and ignition (SLI) and battery-powered uninterruptable power supplies (UPS). Lead acid battery cell consists of spongy lead as the negative active material, lead dioxide as the positive active material, immersed in diluted sulfuric acid electrolyte, with lead as the current collector:
When the lead-acid cell is charged, the lead oxide on the positive plates changes to lead peroxide, and that on the negative plates becomes a spongy or porous lead. In this condition, the positive plates are brown in color, and the negative plates are gray.