Nickel-cadmium battery

Nickel-cadmium battery (Ni-Cd battery) is a type of rechargeable battery. It was once widely used in portable electronics such as power tools, flashlights, toys and model boats. Since it is considered reliable and robust, it is still used in demanding areas such as aviation safety, medical equipment and emergency lighting.

How do nickel-cadmium batteries work?

Ni-Cd batteries consist of a negative electrode (anode), a positive electrode (cathode), a separator between them and an electrolyte. When fully charged, the cathode consists mainly of nickel oxide hydroxide (NiO(OH)) and the anode of cadmium (Cd). The electrolyte is usually a potassium hydroxide (KOH) solution. The anodes and cathodes, isolated by the separator, can be rolled into a spiral inside the case to provide a high maximum current. When using the battery, nickel oxide hydroxide reacts with water, producing nickel hydroxide and hydroxide ions. On the anode, cadmium reacts with the hydroxide ions, releasing electrons that move from the anode to the cathode.

Total reaction during discharge:

2NiO(OH) + Cd + 2H₂O → 2Ni(OH)₂ + Cd(OH)₂

During charging, the reverse reaction takes place.

Advantages and disadvantages

Ni-Cd batteries are extremely reliable and robust. They are difficult to damage, perform well at low temperatures and can also withstand high temperatures. They also have a relatively good cycle life and high discharge rate. For these reasons, they are a good choice for use in harsh conditions and for demanding applications such as in the field of aviation safety.

The two main downsides of Ni-Cd batteries are their high cost and toxicity. Because of this, they have mostly been replaced by nickel–metal hydride and lithium-ion batteries which are cheaper, less toxic and have a higher energy density.

From an environmental standpoint, Ni-Cd batteries are a huge problem. Cadmium is a heavy metal that is highly toxic to organisms. Because of this, the use of Ni-Cd batteries has been restricted in the European Union. They can only be used in emergency systems and lighting and in medical equipment.