Secondary Rechargeable Battery Chemistry

Nickel Cadmium Rechargeable Battery Chemistry

Anode : Cadmium

Cathode : Nickel oxyhydroxide Ni(OH)2

Electrolyte : Aqueous potassium hydroxide (KOH)



The cathode is nickel-plated, woven mesh, and the anode is a cadmium-plated net. Not to diminish any environmental issue, the cadmium is just a coating. The electrolyte, KOH, acts only as an ion conductor and does not contribute significantly to the cell's reaction. That's why not much electrolyte is needed, so this keeps the weight down. (NaOH is sometimes used as an electrolyte, which doesn't conduct as well, but also doesn't tend to leak out of the seal as much).

Ni-Cd rechargeable batteries perform well in high-discharge and low-temperature applications. They also have long shelf and use life. Disadvantages are lower power densities. The memory effect is a temporary loss of cell capacity, which occurs when a cell is recharged without being fully discharged. This can cause cadmium hydroxide to passivate the electrode, or the battery to wear out. A few cycles of discharging and charging the cell will help correct the problem, but may shorten the lifetime of the battery. The true memory effect comes from experience with a certain style of Ni-Cd in space use, which were cycled within a few percent of discharge each time.An important note about "conditioning " a Ni-Cd battery is that the deep discharge spoken of is not a discharge to zero volts, but to about 1 volt per cell.