Ni-MH batteries or the Nickel- hydroxide battery was first introduced in the market as a variation to Nickel Hydrogen battery. Ni-MH batteries is a secondary cell since it is rechargeable. Ni-MH batteries was first patented in 1986 by Stanford Ovshinsky and the first Ni-MH batteries for consumer market was introduced in the year 1989. By the late nineties, Ni-MH batteries replaced Ni-Cd cells in almost all the products all over the world as the preferred rechargeable battery.
- Constitution of Ni-MH cell:
The Ni-MH cell has positive electrode of Nickel oxide hydroxide, the same as in Ni-Cd cell. The negative electrode is made of hydrogen absorbing alloy and the electrolyte used is usually potassium hydroxide with a separator placed inside the cell to ensure that the positive and negative electrodes do not come in contact with each other which otherwise may lead to short circuit.
- Advantages of Ni-MH cell:
When compared to the Ni-Cd cell, the negative electrode substitution in the Ni-MH batteries results in higher electrical capacity for a given volume and weight. This means almost 50% more energy density than Ni-Cd cell. Now this energy density can be advantageous in two ways. You either increase the run time or reduce the space of the battery as per requirement.
It operates at a wide temperature range. It operates at extremely low temperatures, as low as -20 degree Celsius.
Rapid charge and discharge is possible. This works efficiently at higher rate discharges.
It can be charged/ recharged many number of times.
When compared to Ni-Cd battery, it is less prone to memory loss.
It is rugged and easy to store. Only thing is it needs to be recharged when used again after a long time and it charges fast.
The Cadmium present in Ni-Cd battery is toxic. That was one of the reasons why Ni-MH scored over Ni-Cd battery. So Ni-MH is more environment friendly than Ni-Cd battery.
Ni-MH has a longer life span when compared to Ni-Cd battery.
The only problem with the Ni-MH batteries was its high self discharge rate when compared to the Ni-Cd battery. But this has also been solved using an improved separator and an improved positive electrode with slight dip in the electrical capacity capability of the battery.
- Uses of Ni-MH batteries:
Ni-MH batteries are used in digital cameras with flashlights where they over perform over the primary alkaline cells. They are typically used in high drain devices where they give better results than primary cells. They are also used in some of the hybrid electric vehicles, but recent research has showed that they might be the new preferred choice due to their high energy density.
Finally, Ni-MH scores over some other batteries due to its long life and its good safety features and also because it is environment friendly.