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Battery and working principle

Short answer

A battery converts chemical to electrical energy via redox reactions. In a lead-acid battery, discharging reacts lead and lead dioxide with sulfuric acid to form lead sulfate and water, producing 2 V per cell; charging reverses the reaction, restoring acid density.

Write about battery along with the working principle of any one type.

A battery is an electrochemical device that stores chemical energy and converts it into electrical energy through redox reactions. It consists of one or more cells; each cell has a positive electrode (cathode), a negative electrode (anode), and an electrolyte, with a separator between the electrodes. Primary batteries cannot be recharged (alkaline), while secondary batteries can (lead-acid, Li-ion).

Working principle (lead-acid battery as example)

Electrodes: lead dioxide (PbO₂) positive plate, spongy lead (Pb) negative plate, electrolyte of dilute sulphuric acid (H₂SO₄). Each cell gives about 2 V.

Discharging (supplying current to the load)

  • Negative plate: Pb + SO₄²⁻ → PbSO₄ + 2e⁻
  • Positive plate: PbO₂ + 4H⁺ + SO₄²⁻ + 2e⁻ → PbSO₄ + 2H₂O
  • Overall: Pb + PbO₂ + 2H₂SO₄ → 2PbSO₄ + 2H₂O Both plates become lead sulphate and the acid becomes weaker (the density falls).

Charging (reverse reaction with an external source)

  • 2PbSO₄ + 2H₂O → Pb + PbO₂ + 2H₂SO₄ The acid density rises again (about 1.28 g/cm³ when full).
   (-) Pb plate | H2SO4 | PbO2 plate (+)
        e- --> load --> e-

Uses: vehicles, UPS and inverters, solar home systems in Nepal. Advantages: cheap, reliable, high surge current. Drawbacks: heavy, low energy density (30–50 Wh/kg), limited cycles, and lead toxicity.

✓ Answer checked by Claude Opus 5.5 (high effort)

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