NiMH vs NiCd
Batteries are essential household necessities. Although most of the equipments are now directly working with the electricity, a lot of other small or portable devices need batteries. For example, alarm clocks, remote controllers, toys, torches, digital cameras, radios are working with the current supplied by a battery. Using batteries are safer than using main electricity directly. There are a lot of batteries under various brand names in the market today. Except the brand names, these batteries can be divided into various categories according to the mechanism of generating electricity, depending on the ability to recharge or not, etc. NiMH and NiCd batteries are two types of batteries, which are rechargeable.
Nickel-metal hydride cell is abbreviated as NiMH. It is a rechargeable battery which was appeared first in 1989. A battery is an electrochemical cell with an anode and a cathode which produces electricity through a chemical reaction. In NiMH also there is a cathode and an anode. The negative electrode of NiMH is hydrogen absorbing alloy, and the positive electrode is a nickel oxyhydroxide (NiOOH). Alloy is a metallic solid mixture composed of two or more elements. When NiMH first came into the market, the alloy used as the negative electrode was sintered Ti2Ni+TiNi+x alloys. Later, it was replaced with high energy hybrid alloys, which we can see today in the batteries of hybrid cars. NiMH has a higher capacity compared to NiCd batteries. A problem in earlier NiMH was that they tend to lose the charge more quickly. This may be due to the heat produced. And self discharged batteries require more frequent charging which in turn leads to low battery life. But later more sophisticated batteries were developed, which retains their charge longer. These batteries are known as batteries (LSD). When charging NiMH, a voltage range of 1.4–1.6 V/cell should be supplied. Normal AA NiMH battery will have a charge capacity of 1100 mA•h to 3100 mA•h at 1.2 V. Rechargeable NiMH is used in more environmentally friendly hybrid cars like Prius, Lexus (Toyota), Civic, Insight (Honda). Further, they are used in electronic devices, which are portable. NiMH is more environmental friendly and has less toxicity.
Nickel cadmium cells are abbreviated as NiCd. The negative electrode of this battery is cadmium, and the positive electrode is nickel oxyhydroxide (NiOOH). Due to the presence of cadmium, these batteries are more toxic. These batteries are often used in portable electronic devices and toys. Usually when using a battery pack consisting of more than one cell is used to get the required current. NiCd cells have a nominal cell potential of 1.2 volts. Compared to other acid batteries, NiCd batteries last longer without discharging.
What is the difference between NiMH and NiCd?
• The capacity of a NiMH is higher than (normally three times higher) the capacity of a nickel cadmium battery.
• The negative electrode in a NiMH is a hydrogen-absorbing alloy, whereas, in NiCd batteries, it is Cadmium. But the positive electrode in both the batteries is nickel oxyhydroxide.
• NiCd are toxic than the NiMH batteries because of the presence of cadmium. Hence, NiMH is more environmentally friendly than than NiCd batteries.
• NiMH batteries are cost effective than the NiCd batteries.
• NiCd batteries have a lower discharging rate.