Ni-CD can be rechargeable up to 1000s times and use nickel oxide in its positive electrode (cathode), a cadmium compound in its negative electrode (anode), and potassium hydroxide solution in its electrolyte. Ni-CD is best used in high-current demand applications like cordless phones, electric tools, Game Boys and toys.
Ni-CDs have some disadvantages, they are:
· They contain a heavy metal called Cadmium. Cadmium when discarded in the environment does not readily break down and is responsible for certain illnesses in humans.
· Ni-CDs must be fully discharged before recharging to protect against loss of capacity or memory effect.
Thus, Ni-CDs cannot be short charged for connivance to top up their capacity.
(i.e. once a Ni-CD is short charged it will only ever recharge up to that same reduced capacity level.) They will however provide good performance and last a long time if well cared for.
Nickel-Metal Hydride Batteries
Ni-MH has almost twice the power of Ni-CDs and uses hydrogen absorbing alloys in its negative electrode (anode) and nickel oxide in its positive electrode (cathode).
Since their release (the first in the world in October 1990) Nickel-Metal Hydride batteries have developed a strong reputation for high capacity, high performance and high quality and are now used in cellular phones and other applications were you would use a Ni-CD. Ni-MH batteries are becoming more widely accepted and appear to be the way of the future.
Their disadvantages are that they have a higher internal resistance and a higher leakage rate. I.e. they produce a lot more heat when discharging and recharging than Ni-CD batteries and they do not hold their charge for as long a period. Heat build up can restrict how fast they can be discharged & recharged for some applications like RC car racing etc. Additionally to prevent high leakage rates they need to be regularly exercised. (Cyclic charging & discharging)
Their big advantage is that they can be short charged without affecting their capacity and unlike Ni-CDs, they do not have a heavy metal (Cadmium) component, thus they are more environmentally friendly and less dangerous to humans.
last years project