Working Principle Of Lead Acid Battery

Working Principle Of Lead Acid Battery

Date:Mar 22, 2021

The principle equation of charge and discharge chemical reaction of lead-acid battery is as follows:


Discharge: when the battery outputs electric energy to the external circuit, it is called discharge. When the battery is connected to the external circuit for discharge, sulfuric acid will react with the active substances on the positive and negative plates to form the compound "lead sulfate". The longer the discharge time is, the thinner the sulfuric acid concentration is, the less the "liquid" in the battery, and the lower the voltage at both ends of the battery.

The chemical reaction process is as follows:


PbO2 + 2h2so4 + Pb → PbSO4 + 2H2O + PbSO4 (discharge reaction)


Charging: the battery obtains electric energy from other DC power sources, which is called charging. During charging, the lead sulfate on the positive and negative plates will be decomposed and reduced to sulfuric acid, lead and lead oxide. At the same time, hydrogen will be produced on the negative plate and oxygen will be produced on the positive plate. As the concentration of acid in the electrolyte increases, the voltage at both ends of the battery increases. When the lead sulfate on the positive and negative plates is reduced to the original active material, the charging is over.


During charging, the oxygen and hydrogen generated on the positive and negative plates will "oxygenate" into water inside the battery and return to the electrolyte.


The chemical reaction process is as follows:


PbSO4 + 2H2O + PbSO4 → PbO2 + 2h2so4 + Pb (charging reaction)


From the above chemical reaction equation, it can be seen that when the lead-acid battery is discharging, the active material lead dioxide of the positive electrode and the active material lead metal of the negative electrode react with the sulfuric acid electrolyte to form lead sulfate, which is called "bisulfate reaction" in electrochemistry. At the end of battery discharge, the lead sulfate formed by positive and negative active materials is a kind of crystal with loose structure and fine crystal, which has high activity. In the process of battery charging, the loose and fine lead sulfate in the positive and negative electrodes will be reduced to lead dioxide and metal lead under the action of external charging current, and the battery will be in a fully charged state. It is this reversible electrochemical reaction that makes the battery realize the function of storing and releasing electric energy. The repair process takes about 10 ~ 20 hours, and it is converted into charging for 3 hours.


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