The lead-acid batteries are one of the oldest types of rechargeable battery which were invented in 1859 by French French physicist Gaston Plante. Despite having a small energy-to-volume ratio and very low energy-to-weight ratio, its ability to supply high surge contents reveals that the cells have a relatively large power-to-weight ratio.
Lead acid batteries come under the secondary battery. The chemical reactions that occur in secondary cells are reversible. The reaction uses an ingredient known as reactant when the battery delivers current that can be reproduced by passing current through the cell in opposite direction.
The chemical process of extracting current from a secondary battery which is forward reaction is called discharge. The method of regenerating active material is called charging.
Sealed Lead Acid Battery
The sealed lead acid battery consists of six cells mounted side by side in a single case. The cells are coupled together, and each 2.0V cell adds up to the 12.0V overall capacity of the battery. Lead-acid batteries are too heavy, but still better than the lightweight options because lead acid batteries can deliver large surges of electricity required to start a cold automobile engine.
A completely charged lead-acid battery is made up of a stack of alternating lead oxide, isolated from each other by layers of porous separators. All these parts exist in a concentrated solution of sulfuric acid. Intercell connectors connect the positive end of one cell to the negative end of the next cell hence the six cells are in series.
When the battery is discharged, it acts as a galvanic cell, and the following reaction occurs.
Pb(s) + HSO4– + H2O(l) –> 2e– + PbSO4(s) + H3O+(aq)
PbO2(s) + HSO4–(aq) + 3H3O+(aq) + 2e– –> PbSO4(s) + 5H2O(l)
Lead sulfate is formed at both the electrodes. Two electrons are also transferred in the complete reaction. The lead acid battery is packed in a thick rubber or plastic case to prevent leakage of the corrosive sulfuric acid.
Lead Acid Battery Charging
The sulfuric acid existing in the lead discharge battery decomposes and needs to be replaced. Sometimes, the plates change their structure by themselves. Eventually, the battery becomes less efficient and should be charged or changed.
The worst thing that can happen to a car battery is to spend its maximum time in discharged state. This forms a lot of lead sulfate to build up that it is next to impossible to remove. That’s the reason the lead acid batteries must be charged as soon as possible to prevent building up of lead sulfate. Charging of the lead batteries is usually done by providing an external current source.
A plug is inserted which is linked to the lead acid battery and an entirely opposite reaction occurs. Sometimes, charging cannot be performed efficiently if the sulfuric acid or one of the other substance have already decomposed. That’s the reason you need to check them time to time to assure the efficiency of the battery
The reaction that takes place while recharging is as follows;
2e– + PbSO4(s) + H3O+(aq) –> Pb(s) + HSO4– + H2O(l)
PbSO4(s) + 5H2O(l) –> PbO2(s) + HSO4–(aq) + 3H3O+(aq) + 2e–
While recharging, the automobile battery functions like an electrolytic cell. The energy required to drive the recharging comes from an external source, such as an engine of a car. It is also important to note that overcharging of the battery should not take place. If it does, the byproducts like oxygen and hydrogen gas formed will escape, and that will be a loss to the battery.