Question

What happens when lead storage battery is discharged?

Answer 1

When a lead storage battery (commonly known as a lead-acid battery) is discharged, the chemical reactions inside the battery change, causing a loss of stored energy. Here's a simplified explanation of the process:

1. Chemical Reaction During Discharge:
   

   - Inside the lead-acid battery, there are two main parts: the positive plate made of lead dioxide (PbO₂) and the negative plate made of lead (Pb).
   - When the battery is discharging (i.e., providing power), a chemical reaction occurs where the lead dioxide (PbO₂) at the positive plate reacts with sulfuric acid (H₂SO₄) in the electrolyte. This produces lead sulfate (PbSO₄) and water (H₂O).
   - At the negative plate, the lead (Pb) reacts with sulfuric acid, also forming lead sulfate (PbSO₄) and water.

1. Results of the Discharge:
   

   - As the battery discharges, lead sulfate (PbSO₄) forms on both the positive and negative plates.
   - The sulfuric acid in the electrolyte becomes diluted as water is formed in the process, reducing the concentration of the acid.

1. Voltage Decreases:
   

   - As the battery discharges, the chemical reactions reduce the amount of energy stored in the battery. The voltage output drops, and eventually, the battery cannot supply power efficiently.

1. End of Discharge:
   

   - When the battery is fully discharged, the plates are coated with lead sulfate, and the electrolyte becomes mostly water with a very low concentration of sulfuric acid. At this point, the battery can no longer supply power until it is recharged.

1. Recharging:
   

   - When recharged, the battery undergoes a reverse reaction where lead sulfate is converted back into lead and lead dioxide, and the sulfuric acid concentration is restored in the electrolyte.

In short, when a lead storage battery is discharged, the lead plates become coated with lead sulfate, and the electrolyte’s acid concentration decreases, reducing the battery's ability to generate electricity.