NICKEL-CADMIUM CELL (or) NICAD BATTERY

NICKEL-CADMIUM CELL (or) NICAD BATTERY
This is also a rechargeable battery. It consists of a cadmium anode and a metal grid containing a paste of NiO2 cathode and an alkaline KOH.

Cell representation:
Cd │ Cd(OH)2 ││ KOH (aq)│ NiO2 │ Ni

Working (discharging)
When the NiCAD battery operates, cadmium is oxidised to Cd2+ ions and insoluble Cd(OH)2 is formed .

At anode
Cd(S)+2OH¯ --> Cd(OH)2 (s) + 2e¯
(Oxidation of Cd to Cd2+ ions and formation of Cd(OH)2)

At cathode
NiO2(s) + 2H2O + 2e¯---> Ni(OH)2 (s) + 2OH¯
(Reduction of NiO2 to Ni2+ ions and formation of Ni (OH)2)

Overall reaction during use (discharging)

Cd(s)+ NiO2 + 2H2O --> Cd(OH)2(s) + Ni(OH)2 (s) + Energy
From the above cell reactions it is clear that, there is no formation of gaseous products, the products Cd(OH)2 and Ni(OH)2 adhere well to the surfaces. This can be reconverted by recharging the cell.

Recharging the Battery
The recharging process is similar to lead storage battery. When the current is passed in the opposite direction, the electrode reaction gets reversed. As a result, Cd gets deposited on anode and NiO2 on the cathode.

The net reaction during charging is
Cd(OH)2 (s) + Ni(OH)2 + Energy--> Cd (s) + NiO2(s) + 2H2O

Advantages

1. It gives a constant voltage of 1.4V.
2. It is smaller and lighter.
3. It has longer life than lead storage cell.
4. Like a dry cell, it can be packed in a sealed container.

Disadvantages
It is more expensive than lead storage battery.

Uses
It is used in calculators, electronic flash units, transistors and cordless appliances.