11: Memory effect of lithium-ion batteries Part 1

Although it is not necessary to think about the memory effect in lithium-ion batteries, it becomes a big problem with Ni-Cd batteries and Ni-MH batteries.

What is memory effect?
When discharging Ni-Cd batteries and Ni-MH batteries, when charge and discharge are performed before the battery voltage sufficiently drops, that is, with some capacity remaining, it refers to a phenomenon in which the voltage slightly lowers near the point where the discharge was stopped for the first time.

This tendency prominently appears when stopping in the midst of discharge each time.
If discharge continues thereafter, characteristic voltage behavior occurs near the point where discharge was stopped.
Because the battery memorizes (memory) the history that was received through discharge, it is called the memory effect.
The memory effect of Ni-MH batteries can be solved by performing temporary and deep discharge.

Lithium-ion batteries
Even if charge and discharge are performed in lithium-ion batteries, the memory effect does not occur.
Therefore, it means the replenishment charge on top of the data can be performed.
However, if the replenishment charge is being done in lithium-ion batteries, deterioration of the batteries will occur.

In addition, the degree of deterioration of lithium-ion batteries varies depending on the preservation state.
Deterioration of lithium-ion batteries becomes bigger as the storage temperature is higher and charging state is nearly 100%.

If the charge amount is 30% or less and the storage temperature is 15°C or less, the capacity deterioration will be around several% in one year,it may deteriorate to the capacity level of about 60% in 6 months at full charge with the storage temperature of 45°C.

People who charge mobile phones and so on every night will always be preserving the batteries in a fully charged state.
If they go out in such a state or leave it in a car, the battery will be in a high temperature state and deterioration of the lithium-ion cell will progress.

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