Nickel-metal hydride Ni-MH batteries began to be developed in 1970 as a result of the invention of a method for storing hydrogen in nickel-hydrogen batteries. Nickel-hydrogen batteries are still used mainly in satellite equipment. They are bulky, have high pressure tanks for storing hydrogen, and each one costs thousands of dollars..
Nickel-metal hydride Ni-MH batteries, a brief description, application, main advantages and disadvantages.
In early experiments with nickel-metal hydride Ni-MH batteries, metal hydride alloys were unstable in their environment, and the required battery capacity could not be achieved. Therefore, their development was delayed until, in the 80s of the last century, new metal hydride alloys were developed that worked stably. Since then, the design of nickel-metal hydride batteries has been continuously improved towards increasing their energy density.
The success in the distribution of nickel-metal hydride Ni-MH batteries was ensured by the high energy density and non-toxicity of the materials used in their manufacture. Compared to nickel-cadmium, modern nickel-metal hydride batteries have a higher – almost 40% – energy density. There is an opportunity to further increase it, but not without some undesirable side effects..
Like nickel-cadmium, nickel-metal hydride Ni-MH batteries have a high self-discharge capacity. If nickel-cadmium batteries lose 10% of their capacity in the first 24 hours after charging, which then decreases by about 10% every month, then nickel-metal hydride batteries lose 1.5 times more capacity over the same time.
The selection of metal hydride materials that improve hydrogen bonds and reduce alloy corrosion can reduce the rate of self-discharge. However, this increases the price and decreases the energy density of the battery.
When charging nickel-metal hydride Ni-MH batteries, reactions occur in positive plates:
Ni (OH) 2 + OH – NiOOH + H2O + e.
For negative plates:
M + H2O + e – MHp + OH.
where M is an alloy that absorbs hydrogen. Npogl – hydrogen absorbed by the alloy.
When discharged, reverse reactions occur. Nickel-iron, manganese-zinc, manganese-nickel and lanthanum-nickel alloys are used as a hydrogen absorber.
At one time, nickel-metal hydride Ni-MH batteries gradually replaced nickel-cadmium batteries when used as a power source. When asked whether the quality and energy capacity of nickel-metal hydride batteries will improve in the near future, experts say that they will improve, but only slightly. Therefore, a gradual transition to more advanced lithium-ion batteries is considered the most promising..
Benefits of Ni-MH Ni-MH batteries:
The capacity is 30-40% higher than the capacity of nickel-cadmium batteries. There is potential for increasing their energy density.
Significantly less than that of nickel-cadmium batteries, exposure to the “memory effect”. But you can not say about his absence at all.
Easy storage and transportation. No regular monitoring required.
Environmentally friendly. Contain only very mild toxins, recyclable.
Disadvantages of nickel-metal hydride Ni-MH batteries:
Limited service life, especially at high load currents. Capacity decreases after 200-300 charge / discharge cycles. In operation, partial discharge is preferable to full discharge..
Limited discharge current. Although nickel-metal hydride Ni-MH batteries allow high discharge currents, repeated discharges at such currents significantly reduce battery life. The best results when using batteries are obtained if the discharge current is 0.2-0.5C. C – Capacity – battery capacity.
The need for a more complex charge algorithm, since a large amount of heat is released in its process.
High self-discharge. Almost 50% larger than nickel-cadmium batteries. New chemical additives reduce self-discharge, but the energy density of batteries also decreases..
When stored at elevated temperatures, the battery capacity decreases. Ni-MH Ni-MH batteries should be stored in a cool place with approximately 40% charge..
The need for care. Nickel-metal hydride batteries periodically require a control-training cycle (full discharge / charge) to prevent crystallization.
Relatively high prices. Nickel-metal hydride batteries prices are on average 20% higher than similar nickel-cadmium batteries.
Based on the book Battery.