In these batteries, the electrolyte is 21 % by weight aqueous solution of KOH. The cell can be represented as
Cd
KOH
NiO(OH)
anode ....... cathode
Cd + 2 NiO ( OH ) + 2H2O Cd ( OH )2+ 2 Ni ( OH )2
The voltage of single Ni-Cd cell is 1.3 to 1.4 V. Compared to a lead storage battery, this battery has a longer life. It is also available as a sealed unit for use in electronic flash units (photography) and in calculators.
The search is on for more efficient batteries for the following features:
(i) storing electric power generated during the hours of low consumption, for later use during the periods of peak consumption
(ii) storing electricity form solar and wind-powered generators, and
(iii) use in developing quietly-running, non-polluting electric automobiles and mopeds. Though the lead-acid and the Ni-Cd batteries have been used to replace the internal combustion engines of automobiles, their performance is not as good as the gasoline-powered vehicles. Lithium or sodium-sulphur batteries have been developed for this purpose.
Their drawbacks are:
(a) higher temperatures required for efficient operation,
(b) use of metals capable of violently reacting with water, and
(c) the necessity of using corrosion resistant materials.
KOH
NiO(OH) 
Cd ( OH )2+ 2 Ni ( OH )2
