Silver oxide primary cells. Lead-acid battery. Nickel-iron battery

Silver oxide primary cells

Silver oxide positive electrode in the cell gives better voltage than mercury cells. They are also often made in the shape of a small disc.

Lead-acid battery

This is a secondary cell because it can be recharged. It generally con- sists of three or six cells connected in series.

The electrolyte used is a solution of sulfuric ac- id (H₂SO₄), the negative electrode consists of lead (Pb) and the positive electrode is made of lead dioxide (PbO₂). This type of battery is used mostly in cars, trucks, air planes and other vehi- cles. Its major advantage is that it can give a very large electric current for starting an engine.

A lead-acid storage cell goes flat when

sulfuric acid is gradually converted into water and the electrodes are con- verted into lead sulfate (PbO₄). When the lead-acid battery is recharged, these chemical reactions are reversed until the chemicals have been re-

 

stored to their original condition. A lead-acid battery has a useful life of about two to three years and they produce about 2V per cell.

Nickel-iron battery

A secondary cell widely used in heavy industry is nickel-iron battery. The principle of operation is the same as in the lead-acid cell. The only exception is that the negative electrode consists of iron and the positive electrode is made of nickel oxide (Ni₂O₃). The electrolyte is a solution of po- tassium hydroxide (KOH). The nickel-iron cell has the dis-

advantage of emitting hydrogen gas during charging.

Cadmium battery (nickel-cadmium cell)

This is also very similar to nickel-ion battery. Here negative iron electrode is replaced by cadmium electrode. The positive electrode is nickel oxide. Some nickel-cadmium batteries gradually lose their maximum energy capacity if they are repeatedly recharged after being only partially dis- charged – this phenomenon of losing energy capacity is called “memory effect”.