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Nickel Cadmium (NiCd)

Characteristics of Nickel Cadmium

These cells use nickel hydroxide Ni(OH)2 for the positive electrode (cathode), cadmium Cd as the negative electrode (anode) and an alkaline potassium hydroxide KOH electrolyte.

The cells are sealed and use a recombinant system to prevent electrolyte loss and extend the useful life.

Memory effect is one of its biggest drawbacks, as is a fairly high rate of self-discharge at high temperature.  As cadmium is highly toxic, its use in batteries is now banned, with the exception of medical and some military applications.

Performance data

  • Voltage: 1.2V
  • Charge cycles: 1,000 to 1,500
  • Typical energy density: 50 - 70 Wh/kg
  • Typical power density: 150 W/kg
  • Spontaneous discharge: 20% per month

Applications

  • Cameras
  • Medical
  • Medical power tools

Advantages

  • Low internal resistance and can supply high surge currents
  • High rate charge and discharge rate possible (faster than lead acid).
  • Up to 10C discharge rates for short periods
  • Flat discharge characteristic (but falls off rapidly at the end of the cycle)
  • Tolerates deep discharges for long periods with no damage or loss of capacity
  • Charging process is strongly endothermic - the battery cools during charging. This makes it possible to charge very quickly, as the I2R heating and endothermic chemical reaction counteract each other.
  • Rapid charge typically 2 hours, but can be as low as 10 to 15 minutes.
  • The coulombic efficiency of nickel cadmium is over 50% for a fast charge but can drop to below 80% for slow charging.
  • The sealed nickel-cadmium cell can be stored in the charged or discharged state without damage. It can be restored for service by recharging several charge/discharge cycles.
  • Wide temperature range (up to 70°C)
  • Available in a large variety of sizes and capacities

Drawbacks

  • Relatively high susceptibility to memory effect; if the battery is consistently discharged to the same level, then fully recharged, the battery will eventually stop discharging on its own upon reaching this threshold.
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