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Nickel-cadmium battery

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Nickel-cadmium batteries (commonly abbreviated NiCd) are a type of rechargeable battery first developed in 1961. They are commonly used in many portable electronic devices.

Nickel-cadmium cells have a nominal cell voltage of 1.2V and can supply high surge currents. This makes them a favourable choice for remote controlled electric toy aeroplanes, boats and cars.

NiCd batteries contain a nickel oxide positive electrode plate, a cadmium negative electrode plate, a separator, and an alkaline electrolyte. NiCd batteries usually have a metal case with a sealing plate equipped with a self-sealing safety valve. The positive and negative electrode plates, isolated from each other by the separator, are rolled in a spiral shape inside the case.

The chemical reaction which occurs in a NiCd battery is:

<math>2{\rm NiOOH}+{\rm Cd}+2{\rm H}_2O\longrightarrow2{\rm Ni}({\rm OH})_2+{\rm Cd}({\rm OH})_2</math>

With the reaction going to the left when the battery is being discharged and to the right when it is being recharged. The alkaline electrolyte (commonly KOH) does not participate directly in this reaction.

NiCd batteries suffer from a "memory effect" if they are recharged before they have been fully discharged; subsequent discharging will not be able to get as much power out of the battery. NiCd rechargers will sometimes include the ability to fully discharge batteries before beginning recharging as a result. Never, however, discharge rechargeable batteries to zero voltage.

Lazy battery effect is caused by crystalization within the electrolyte reducing the available capacity. Much of the lost capacity can be recovered by a few deep discharge cycles. If treated well, NiCd batteries can last for 1000 cycles or more before capacity drops below 50% of original.

The self discharge rate for nickel-cadmium rechargeables ranges around 20% per month and is considerably less than that of Nickel metal hydride batteries which is around 30% per month. The self discharge rate is highest for full charge state and drops of somewhat for lower charge states. Batteries should be long time stored at around 40% charge.

NiCd batteries contain cadmium, which is a toxic heavy metal and therefore requires special care when the batteries are disposed of. Nickel metal hydride batteries are similar to NiCd, but less toxic.

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