How Everything Works
How Everything Works How Everything Works

Question 680

What is the "memory effect" of a NiCad (nickel-cadmium) battery? Is it reversible or minimizable? - MF
NiCad batteries are more rechargeable than most batteries because the chemicals that power NiCad batteries remain solid throughout the discharge cycle. The chemicals in most other batteries, including alkaline batteries, go into solution or otherwise change shape during the discharge cycle so that it difficult to reconstruct the original battery electrodes during recharging.

Unfortunately, the two solid electrodes in a NiCad battery are damaged by repeated charging and discharging. These electrodes work best when they are both fine powders (the positive electrode is nickel hydroxide powder and the negative electrode is cadmium metal powder). With repeated use, the powder particles grow larger and larger and they stop contributing to the battery's power. "Memory" appears during the discharge cycle when all the useful small particles have been used up and only the undesirable large particles remain. Repeated charging and partial discharging tends to convert many of the small particles into large particles. You can improve the battery by fully discharging it before recharging it, presumably because this deep discharge breaks up the larger particles so that the battery contains mostly small particles once again.


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