Difference Between NiMH and NiCd (With Table)

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The battery is used for electrical power devices like mobile phones, electric cars, flashlights etc., via external connections. It consists of an electrochemical cell. When the battery is powering the electrical devices, then it has a cathode and anode. Earlier, the term battery was meant to consist of multiple cells, but now it is usually referred to as consisting of a single cell. There are two types of batteries primary and secondary. Primary batteries are disposable, while the secondary batteries can be recharged again. Both NiMH and NiCd batteries are rechargeables.

NiMH vs NiCd

The difference between NiMH and NiCd is that the negative electrode used in NiMH is a hydrogen-absorbing alloy. While the negative electrode used in NiCd is cadmium. NiMH stands for Nickel-metal hydride battery, and NiCd stands for Nickel Cadmium battery. The discharging rate of NiMH is higher. While the discharging rate of NiCd is lower. NiCd batteries are more toxic than NiMH batteries. It releases chemicals like lead, mercury, cadmium into the environment.

NiMH or Nickel-metal hydride battery is a secondary battery that means that it can be recharged. The chemical reaction of NiMH in the positive electrode is very much the same as in NiCD, i.e. nickel oxide hydroxide (NiOOH). The negative electrode used in NiMH is a hydrogen-absorbing alloy. It has a higher capacity and higher energy density. But it is less than lithium-ion batteries. NiMH is resistive to explosion and leaking and is used as a substitute for the same shaped non-alkaline and non-rechargeable batteries.

NiCd stands for Nickel-cadmium battery. The abbreviation used for nickel-cadmium battery is derived from Nickel and Cadmium, and hence it becomes NiCd. It is rechargeable better using cadmium as the negative electrode and nickel oxide hydroxide as the positive electrode.NiCd battery has a discharge of around 1.2 volts, and it decreases at the end of a discharge. An electromotive force that is offered by the NiCd battery is 1.3 volt. This battery comes in various sizes and capacities, ranging from large ventilated cells to carbon-zinc dry cells.

Comparison Table Between NiMH and NiCd

Parameters of ComparisonNiMHNiCd
CapacityHighLow
Discharging rateHigherLower
CostExpensiveInexpensive
ToxicityLessMore
EffectEnvironment friendlyNot Environment friendly
ChargingResists over-discharging and overcharging.Simple and quick
Negative electrodeHydrogen-absorbing alloyCadmium

What is NiMH?

NiMH batteries were invented in the year 1967 when work and research began at the Battelle-Geneva Research Center. NiMH batteries were based on the sintering of the NiOOH electrodes and Ti2Ni+TiNi+x alloys. Developing NiMH batteries as we know it now was sponsored by two companies Volkswagen AG and Daimler-Benz. After developing the required and specific energy, patents were filed in various European countries, including Switzerland, Japan and the United States. A patent was then transferred to Daimler-Benz.

NiMH batteries became famous, and interest in it was aroused during the 1970s when it was being used in the satellites. Various companies like Philips, CNRS, Ovonic Battery Co. tried to make NiMH battery light-weighted so that it could store the hydrogen and also improvised the composition of Ti-Ni alloys. In the year 2008, more than 2 million cars consisting of NiMH batteries were manufactured. NiMH batteries are bi-polar which means that it avoids short circuits and has some advantage like storage of hydrogen in the electric vehicles.

NiMH batteries can be charged fast, but while charging, they should be charged with the smart battery charger to avoid overcharging. NiMH battery consists of safety called resettable fuse, which prevents current or temperature from being too high.NiMh is considered better than the other types of batteries. It is used in high-drain devices and digital cameras. It is advantageous because of its ability to draw high current and low internal resistance. NiMH batteries took the place of NiCd batteries because of their nominal charge capacity, operation on many devices etc. Lithium-ion batteries are considered better than NiMH batteries. It is used in hybrid and electric vehicles, but now it is superseded by Li-on batteries.

What is NiCd?

NiCd batteries were invented by Waldemar Jungner in 1899 in Sweden. When NiCd batteries were made, then its competition was the lead-acid batteries. In all the ways Nicd batteries were better than it, like higher energy density etc. Jungner substituted cadmium in place of the iron. His work was not known in the United States. After producing the flooded design in Sweden and using active materials. In 1946, the production of NiCd batteries was first started in the United States. The batteries were called pocket type because of nickel-plated steel pockets.

In the mid of the 20th century, sintered Ni-Cd battery became very popular because of its greater material surface area, lower internal resistance and plates becoming highly porous. Discharging rate of the NiCd batteries depend upon the different size like in a D-size battery the discharge rate is 3.5 amperes, and in AA batteries the discharge rate is 1.8 ampere. The cell potential of NiCd batteries is very nominal, i.e., 1.2 volts. The charging rate of the NiCd battery is very simple and quick and can be charged at different rates depending upon the cell.

Because of fast charging, the temperature of the batteries may rise, which can damage the cells. There is a risk of overcharging, and the life of the battery would be shortened. The safe temperature range to use NiCd battery is between -20°C and 45 °C. When the Ni-Cd batteries are not in use, then it will self-discharge itself, which is one of its drawbacks. Wet cell or Vented cell Ni-cd batteries were also invented in 1899. It is used for larger capacities because of its higher discharge rates. It has wide applications like backup power for telecoms, aviation, mass transit and rail, engine starting for backup turbines etc.

Main Differences Between NiMH and NiCd

  1. The capacity of NiMH batteries is comparatively higher than NiCd batteries.
  2. The discharging rate of the NiMH batteries is higher. The discharging rate of the NiCd battery is lower.
  3. The cost of NiMH is expensive. While NiCd is cost-effective.
  4. NiMH batteries are less toxic. NiCd is more toxic and releases chemicals like cadmium, mercury, nickel etc.
  5. NiMH batteries are more environmentally friendly than NiCd.
  6. NiCd batteries resist over-discharging and overcharging. While NiMH batteries charging is very simple and quick.
  7. The negative electrode used in NiMH is a hydrogen-absorbing alloy. The negative electrode used in NiCd is Cadmium.

Conclusion

Both NiMH and NiCd batteries are rechargeables. NiCd batteries were invented earlier than NiMH batteries. NiMH is a better version of batteries than NiCd. NiMH batteries became very popular in the 21st century, so much that at a time, they constitute three per cent of batteries globally. While Ni-Cd batteries were popular in the mid of the 20th century. NiCd batteries are cheaper than NiMH and are functional in low temperatures. It can take a high number of charges, are easy to store and ship. While NiMh has high capacity than other rechargeable batteries. It is very lightweight in construction and environment friendly.

References

  1. https://www.sciencedirect.com/science/article/pii/S0956053X05000176
  2. https://ieeexplore.ieee.org/abstract/document/4018094/
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