铅酸电池化学

The lead-acid battery’s operation is based on a reversible double sulfate reaction. In a fully charged state, the negative electrode is pure, spongy lead (Pb), and the positive electrode is lead dioxide (PbO₂). Both are immersed in an electrolyte of approximately 37% sulfuric acid (H₂SO₄) in water.

During discharge, the following half-reactions occur. At the anode: [latex]Pb(s) + HSO_4^-(aq) \rightarrow PbSO_4(s) + H^+(aq) + 2e^-[/latex]. At the cathode: [latex]PbO_2(s) + HSO_4^-(aq) + 3H^+(aq) + 2e^- \rightarrow PbSO_4(s) + 2H_2O(l)[/latex]. In both reactions, the active material is converted to lead sulfate, and sulfuric acid is consumed while water is produced. This consumption of sulfuric acid causes the specific gravity (density) of the electrolyte to decrease, providing a simple and effective way to estimate the battery’s state of charge using a hydrometer.

To recharge the battery, an external voltage is applied, forcing the reactions to run in reverse. Lead sulfate on the negative plate is converted back to lead, and lead sulfate on the positive plate is converted back to lead dioxide. The water is consumed, and sulfuric acid is regenerated, increasing the electrolyte’s specific gravity. Despite its low energy-to-weight ratio and the environmental hazards of lead, the technology’s low cost, reliability, and ability to supply high surge currents have ensured its continued widespread use, especially in automotive applications.