The nickel-cadmium secondary, i.e. rechargeable battery or cell incorporates cadmium as an active negative electrode material. This technology is based on the reversible electrochemical reactions of cadmium and nickel in a potassium hydroxide (alkaline) electrolyte. At the negative electrode (cathode), cadmium oxide further oxidizes to cadmium hydroxide on discharge whilst the hydrated nickel compounds at the positive electrode (anode) are reduced to nickel hydroxide, thus:
2Ni(OH)2+Cd(OH)2 <-- charge/discharge --> 2NiO OH + Cd + 2H20
The potassium hydroxide electrolyte takes no part in the charge-discharge reactions and acts only as a charge carrier. Lithium hydroxide may be added to the electrolyte to increase the life of the positive electrode. The reaction produces a nominal usable electromotive force of 1.2 volts per cell.
A number of types of cell constructions are possible. These variations in cell construction lie mostly in the nature of electrode support utilised.
For the positive electrode three principal types are recognised - pocket plate, sintered plate and fibre plates. An electrode support is necessary because the active material (nickel hydroxide) is usually in powder form and held in pocket plates or mixed with binders or paste and placed in sintered or fibre electrodes. it should be noted that nickel hydroxide swells appreciably during charge and discharge, strains the support and restricts the choice of support type at the positive electrode.
Negative electrode designs make use of a broader range of structures including pocket plates, nickel sintered , fibre, and plastic bonded supports. It is the physical stability of the active material (cadmium oxide) in the negative electrode that permits such a wide variety of support materials.
Furthermore, graphite or iron oxide needs to be added to improve the conductivity of both nickel and cadmium hydroxide. Furthermore, in all cell construction types, a separator is placed between the two electrodes to prevent short circuits.
Nickel-cadmium batteries are characterised by their resistance to mechanical and electrical abuse, long calendar and cycle life, their superior ability to operate with limited performance loss in both cold and hot temperatures as well as in settings with large temperature swings, limited maintenance requirements and superior reliability. Furthermore, they do not display the “sudden death” syndrome which is prevalent in the standard (industrial) battery technology.
Based on these features, they are used in applications where these features are absolutely essential, such as mission critical industrial settings as well as situations where human life is at stake.
Ni-Cd batteries are of two types: portable batteries and industrial batteries.
(a) Portable nickel-cadmium batteries
Ni-Cd batteries for portable use are of the sealed type and are generally of sintered plate construction and the cells are of the cylindrical format. These nickel-cadmium batteries are used in consumer electronic equipment such as cordless portable tools, toys and other domestic cordless appliances.
The placing on the market of Ni-Cd portable batteries has been restricted in the European Union since 2008 for most uses, with a limited number of exemptions. The largest exemption for use in cordless power tools has been discontinued on December 31st, 2016.
(b) Industrial nickel-cadmium batteries
Dues to their very unique advantages, industrial Ni-Cd batteries are the technology of reference for both civilian (Airbus, Boeing, Embraer and others) and military aircrafts where they are used to provide back-up power for avionic systems when the principal power source fails, and also to start engines on the ground.
Industrial Ni-Cd batterie are also widely used as back-up power in railways and underground metro systems for emergency braking, coach lighting, heating and air conditioning, driver to passenger communication, as well as locomotive starting and trackside back-up power for signaling and warning lights.
Other uses include back-up power for large industrial assets such as nuclear power plants, steel mills, sea-based oil exploration and extraction platforms, refineries, emergency lighting an alarm systems, as well as in navigation assets such as lighthouses and buoys, and other uses in which the same characteristics, in which unmatched reliability usually rates the highest, are required.
The International Cadmium Association (ICdA) is a non-profit association representing the interests of the world’s cadmium industry. Its Members include producers, processors, recyclers and consumers of cadmium metal, cadmium compounds, and products to which cadmium or its compounds have intentionally been added.
Read more ?