Raw materials in battery technology: Cadmium (Glossary)

Cadmium is a soft, malleable and rollable, silvery-white metal from the group of the so-called transition elements. It is very similar to zinc but nobler. It is stable in air. Cadmium is insoluble in lyes, it is hardly attacked by hydrochloric and sulphuric acid, but heavily attacked by oxidising acids

The world production of cadmium is around 18,000 tons per year, of which 60% is used to build accumulators. Cadmium is always manufactured as a side-product of zinc extraction. Important production countries include the USA, Canada, Australia and the CIS countries.

Cadmium, its compounds and vapours are toxic. Excessive cadmium absorption can lead to a chronic Itai-Itai disease, the metal is also carcinogenic.

Cadmium was used., for example, as an alloying metal for alloys with a low melting point (e.g. in soldering tin) or as a cadmium coat for the rustproof finishing of metals (cadmium-plating). Today, cadmium has been largely replaced by other materials on account of its toxicity.

In battery technology, cadmium is mainly used as a material for anodes in ni-cd batteries, where it accounts for 10 to 20% of the weight. Metallic cadmium is oxidised to cadmium hydroxide at the anode during accumulator discharging. Such anodes are not made of solid cadmium but are generally a steel sheet onto which a cadmium sponge has been applied. Since the equilibrium potential of the cadmium electrode is only slightly above that of hydrogen development, an oxygen cycle can be realised in nickel-cadmium cells and gassing thus largely prevented. Consequently, NiCd cells can be manufactured in a gasproof design. On account of the toxicity of cadmium, NiCd accumulators are being increasingly replaced by nickel-metal hydride accumulators despite their excellent ratings.

See also: Ban on cadmium and mercury

Some key technical data

Chemical symbol: Cd

Atomic number: 48

Relative atomic mass: 112.4

Oxidation numbers: +2, +1

Density: 8.65 g/cm³

Melting point: 321°C

Boiling point: 767°C

Specific electrical resistance: 7

	See also:
		Glossary overview Nickel-cadmium accumulators (Glossary) Ban on cadmium and mercury

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