How does battery degradation work?

Question

Let’s say I have a smartphone or an electric car, it loses 10% of the capacity.

Does it mean that the system consumes 10% more power, or the capacity just lowered, making me spend less electricity/money to charge?

In: Chemistry

Answer 1

>the capacity just lowered, making me spend less electricity/money to charge?

This one.

As for how, it’s to do with the degradation of the materials in the battery. That degradation can take several forms.

The main thing to know is that in a lithium battery, the lithium ions needs to move freely. Anything that prevents that will cause loss of capacity and other unwanted effects.

The simplest one is that the lithium reacts with other molecules in the battery to form some undesired compound and is functionally lost, it cannot move freely as an ion.

Another is the degradation of the electrodes. This can also work in two ways.

One is preventing the lithium from leaving, again locking it away and making it functionally lost.

But even if it isn’t completely prevented from leaving, it can be harder to get out. You need to apply higher voltage while charging.

And the thing is, battery charging in devices is voltage limited. A battery, and the device it powers, doesn’t actually know how “full” the battery is.

Batteries never charge and discharge from 0 to 100%. More often it’s something like 10-90, or even 20-80.

There’s set voltages defined by a manufacturer where the battery is “almost full” and “yeah, full now”.

So if degradation causes the battery to require that voltage at a lower state of charge, the device just goes “huh, I guess it’s charged now”. Because it doesn’t know better.