Rechargeable Ni-Cd and NiMH batteries provide power for cordless phones, cordless power tools rechargeable batteries for consumer electronics and for hybrid cars.
Nickel, specifically nickel oxyhydroxide (NiOOH) serves as the positive terminal for not one, but two, different types of batteries that fill important roles in our society’s need for portable and plentiful electricity.
Nickel-cadmium batteries, known as Ni-Cd or “Ni-Cad” as trademarked by SAFT Corporation, use cadmium for the negative battery terminal, also known as the cathode.
In Nickel Metal Hydride (NiMH) batteries the cathode may be comprised of up to six different metals to create a system that is electrically reversible to form metal hydride compounds.
Although Ni-Cd batteries are being replaced for some uses, they are ideal for applications that require a high rate of discharge as with remote-controlled electric model airplanes, cordless power tools, and camera flash units. Ni-Cd batteries lose relatively little of their charge over time, so if batteries are stored fully charged, they remain charged for a much longer timespan.
NiMH batteries offer other advantages. They eliminate the toxicity of the cadmium in Ni-Cd batteries and have two to three times the charging capacity of the Ni-Cds, but they have a relatively high self-discharge rate and must be charged immediately prior to use. NiMH battery technology is widely employed in hybrid cars, in which hundreds of individual cells are assembled into a battery pack. These batteries are extremely promising for electric, plug-in cars that operate only on batteries and don’t have the dual, internal combustion engine/battery technology of hybrids.
Both Ni-Cd and NiMH batteries produce 1.2 V, which is lower than the 1.5 rating for alkaline batteries. Under most circumstances, this lower voltage is not a problem. Anyone who has watched a flashlight gradually dim as the batteries wear down is familiar with the diminishing output of alkaline batteries. Since that power may go as low as 1.0 to 0.9 V before the battery is replaced, many applications run equally well on the nickel batteries, which, although they put out a lower voltage, produce a far more consistent energy output over time.