- The reaction in a secondary battery occurs many times.
- Once it exhausts it can be recharged and used again.
- They are recharged by passing electric current through it in opposite direction.
- Example of secondary cell is lead and nickel cadmium cell.
Fig. Lead storage battery
Fig. Nickel-Cadmium cell
- It is used extensively in automobiles and invertors.
- The lead cell contains a lead anode and a lead dioxide (PbO2) cathode and sulphuric acid is used as an electrolyte.
Anode: Pb(s) + SO42–(aq) --> PbSO4(s) + 2e–
Cathode: PbO2(s) + SO42–(aq) + 4H+(aq) + 2e– --> PbSO4 (s) + 2H2O (l)
- The net cell reaction is:
Pb(s)+PbO2(s)+2H2SO4(aq) --> 2PbSO4(s) + 2H2O(l)
- While charging, the reaction within the battery is reversed and PbSO4(s) on anode and cathode is converted into Pb and PbO2, respectively.
- It has a longer life thanlead storage cell and it requires more expenses to
- The net reaction is:
Cd (s)+2Ni(OH)3 (s) --> CdO (s) +2Ni(OH)2 (s) +H2O(l)