NiCd vs NiMH, what are the differences

The main differences between the two types of batteries are capacity, memory effect and environmental friendliness. NiMH batteries have higher capacity, which means that they can generally power your device for longer, also don't suffer from the memory effect and much friendly to the environment.

Before the 1990s, the battery of portable devices was almost entirely nickel-cadmium (NiCd) batteries. Later, in order to solve the strong toxicity problem of NiCd, many features of NiCd were transferred to NiMH because the two systems are similar. Today, due to environmental regulations, NiCd batteries are only used in certain areas.

• Nickel cadmium (NiCd)

Lead acid was the only other rechargeable battery before Waldemar Jungner invented nickel-cadmium batteries in 1899. NiCd has several advantages over lead-acid batteries, but its material is expensive and leads to slow development. It was not until 1932 that the active material was deposited in a porous nickel-plated electrode and further improved by the gas generated during the absorption charging process in 1947 to form a modern sealed NiCd battery.

Since then, NiCd batteries have become the preferred choice for two-way radios, professional cameras, emergency medical equipment and power tools. In the late 1980s, more active material was filled into the battery, and an ultra-high-capacity NiCd battery with a capacity 60% higher than the standard NiCd appeared, which shocked the world. However, the gain is affected by higher internal resistance and fewer cycles.

The standard NiCd is still one of the strongest and most tolerant batteries, and the airline industry still insists on using it, but it requires proper care to achieve longevity. NiCd, and some NiMH, have a memory effect, which means that if a periodic full discharge cycle is not given, it will result in a loss of capacity. The battery seems to remember the energy that was passed before, and once the routine is established, it doesn't want to provide more. The following are the advantages and limitations of standard NiCd.

Advantages:

1. The battery can be super-fast charging and the pressure is small.
2. Rugged, high cycle count
3. Good load performance;
4. Long shelf life; can be stored in a discharge state, need to be activated before use
5. Simple storage and transportation;
6. Good low temperature performance
7. Affordable; NiCd is the lowest cost product per cycle
8. Available in a variety of sizes and performance options

Disadvantages:

1. Lower specific energy compared to newer systems
2. Memory effect; need to be fully discharged periodically to rejuvenate
3. Cadmium is a toxic metal. Cannot be disposed of in landfills
4. High self-discharge; need to be charged after storage
5. Low battery voltage (1.20V) requires many batteries to reach high voltage

• Nickel metal hydride (NiMH)

The study of nickel metal hydride began in the Battler-Geneva Research Center in 1967; however, the instability of metal hydride limits the development of nickel-hydrogen (NiH). The new hydride alloy discovered in the 1980s finally improved stability and was successfully completed in 1987. Today, the specific energy of NiMH is 40% higher than the standard NiCd.

The chemical composition of the standard nickel-hydrogen battery is as follows: an alkaline electrolyte such as a nickel hydroxide positive electrode plate, a hydrogen ion negative electrode plate, a separator, and potassium hydroxide.

Here are some of the advantages of using NIMH batteries:

1.Relatively high capacity compared to other rechargeable batteries, 30-40% higher than standard NiCd capacity

2.Resistance to overcharging and overdischarging

3. Very light structure
4. Environmentally friendly: no cadmium, mercury or lead and other harmful chemicals
5. Most have no memory effect.
6. Simple storage and transportation; unregulated control
7. Nickel content makes recycling profitable
8. Wide temperature range

However, nickel-metal hydride are not without disadvantage:

1. More expensive than NiCd
2. A complex charging algorithm is required. Sensitive to overcharge, does not absorb overcharge well; trickle charge must be kept low
3. Some are only used with the manufacturer's charger
4. The battery is finer than NiCd and it is more difficult to charge
5. Current generates heat during fast charging and high load discharge
6. Performance is not as good as NiCd battery at extreme temperatures
7. Limited service life; deep discharge reduces service life
8. NiMH has a self-discharge rate of 20% in the first 24 hours after charging, and then increases by 10% per month, which is the highest among its kind. Changing the hydride material reduces self-discharge and reduces alloy corrosion, but this reduces the specific energy. Batteries for electric powertrains utilize this improvement to achieve the required robustness and long life.

Application

NiMH has become one of the most accessible rechargeable batteries for consumers. Battery manufacturers want to attract buyers away from disposable alkaline and rechargeable batteries. Now used in car batteries, medical equipment, pagers, mobile phones, camcorders, digital cameras, electric toothbrushes and other low-cost consumer devices.

NiMH batteries for the consumer market are an alternative to reusable renewable alkaline batteries that emerged in the 1990s. Limited cycle life and poor load characteristics hinder its success.

Compare the specific energy, voltage, self-discharge and running time of several batteries. These batteries are available in AA, AAA and other sizes and can be used in portable devices designed for these specifications. Even if the battery voltage may vary, the discharge termination voltage is very common, usually 1V / battery. Portable devices have some flexibility in terms of voltage range. It is important not to mix the batteries and always use the same type of battery in the stand. Safety issues and voltage incompatibility prevent the sale of most lithium-ion batteries in the form of AA and AAA.

High self-discharge is a constant concern for consumers using rechargeable batteries, and flashlights or portable entertainment devices with NiMH batteries need to be recharged after a few weeks of placement. Therefore, it is not suitable for many consumers to charge the device before each use, especially for flashlights and emergency power supplies with very low frequency, while alkaline batteries can remain for 10 years.