Question

Why can a lead storage battery as a secondary cell be recharged?

Answer 1

A lead storage battery, also known as a lead-acid battery, can be recharged because it works on a reversible chemical reaction. Here's how it works in simple terms:

1. Discharging (When it's used): When the battery is being used to power something, the lead (Pb) plates inside the battery react with sulfuric acid (H₂SO₄) to create lead sulfate (PbSO₄) on both plates. This reaction releases electrical energy. The chemical reaction looks like this:
   

   - At the positive plate: PbO₂ + 4H⁺ + 2e⁻ → PbSO₄ + 2H₂O  
   - At the negative plate: Pb + SO₄²⁻ → PbSO₄ + 2e⁻

   This results in a build-up of lead sulfate on both plates, which reduces the battery's ability to store energy.

1. Recharging: When you recharge the battery, you apply an external electrical current, which reverses the chemical reactions. The lead sulfate on the plates breaks down, and the plates return to their original lead dioxide (PbO₂) and lead (Pb) forms. The sulfuric acid in the electrolyte is restored to its original concentration. The chemical reactions during recharging are:
   

   - At the positive plate: PbSO₄ + 2H₂O → PbO₂ + 4H⁺ + 2e⁻  
   - At the negative plate: PbSO₄ + 2e⁻ → Pb + SO₄²⁻

This reversibility of the chemical reactions is what allows the lead-acid battery to be recharged many times.

In summary, the ability to recharge a lead storage battery is due to the fact that the chemical processes involved in discharging and recharging are reversible. When you recharge, you essentially "undo" the discharging process, restoring the battery’s energy storage capacity.