The lead acid battery is a type of secondary battery or can also be known as the Storage battery. This kind of battery is rechargeable and is usually found to have its applications in the car batteries. Although the charge holding capacity to the weight of the battery is very low but due to its cost efficiency the lead acid batteries have a good hold in the auto mobile battery industry.
Materials required for a lead acid battery
The main active materials for making a lead acid battery are
- Anode-lead peroxide
- Cathode-sponge lead and
- Electrolyte-dilute sulphuric acid
At the positive end we have lead peroxide which is hard and brittle whereas the negative end is made of pure lead in soft sponge form. For the electrolyte the ratio of water to acid is 3:1. Please note that the battery container should be of a material which doesn’t react with the sulphuric acid.
What makes the current flow in this battery?
- Both the electrodes i.e. lead peroxide and sponge lead are dipped in the diluted sulphuric acid solution.
- Load is then connected externally.
- In the acid the molecule split into hydrogen ions and sulfate ions.
- The H+ ions reach lead peroxide plate receive electron and become hydrogen atom. This again attacks the lead peroxide and form lead oxide and water.
- This reacts with sulphuric acid and forms lead sulfate and water.
- Sulfate ion move freely and some reach pure lead and become radical sulfate.
- Due to this movement there would be inequality of electrons.
- To balance out this inequality in the electrons on both the sides of the electrodes there would be flow of current
This flow of current to balance out the electrons is known as the discharging process of a lead acid battery.
How does the battery charge again?
- Disconnect the load and connect with a DC source.
- During discharging the density of sulphuric acid falls but it still has the ions.
- Hydrogen being positively charged move to the negative ion of the DC source and become hydrogen atom.
- The hydrogen atom then attacks the lead sulfate and form lead and sulphuric acid.
- The negative ion moves to the positive end of the DC source and gives the extra electron and become radical sulfate.
- This reacts with lead sulfate and forms lead peroxide and sulphuric acid.
- As we can see that we get our electrode and electrolytes back by this process. Hence the battery is now ready for the discharge process.
Although we get back the electrode and electrolytes by this process of charging but the concentration of all the chemicals keeps decreasing with each charge cycle and hence after maximum use the battery dies out and we need to replace it.