NiMH battery is the shorthand used for Nickel-Metal-Hydride battery
. These batteries are similar to the nickel-cadmium batteries with the difference of using cadmium as an active element at the hydrogen absorbing negative electrode.
The main components of NiMH batteries include a Nickel-hydroxide cathode, the anode of hydrogen absorbing alloys and an electrolyte of Potassium-hydroxide. This electrode is composed of a metal hydride containing the alloys of Lanthanum which serves as a solid source of reduced hydrogen. This is oxidized to form protons. The electrolyte developed is of the alkaline potassium hydroxide.
The voltage of NiMH battery is 1.2 volts. The density of this battery is more than the double of the Lead acid and about 40% more than NiCd battery. These batteries are prone to memory effect although to a less extent. They are better for the environment because no mercury or lead is used. The costing of NiMH batteries is more than that of Lead-acid and NiCd batteries.
It has been demonstrated that there are up to 3000 cycles at 100% depth of discharge by using NiMH batteries. These batteries can tolerate over charge and discharge conditions. They have low impedance. Sometimes it may affect the batteries due to overcharging. So, it is advisable to keep timers while charging. These batteries can be operated within wide temperature ranges.
These batteries are mainly used in cameras, mobile phones, pagers, camcorders, medical instruments and many low cost appliances. With the advanced technology, these batteries have found their place in automotive applications where high voltage is required.