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
A battery is a chemical process. There are unwanted side reactions that reduce the amount of useful reactants, causing loss of capacity. This especially happens at the highest and lowest voltages.
The system should consume less energy (joules or watt hours) charging from 0% to 100%. The capacity is lowered, so the battery both charges and discharges faster. The coulombic efficiency should stay the same; it shouldn’t be leaking current uselessly and heating things up. It should cost the same money as usual to add the same amount of energy to the battery.
Atoms that are positively or negatively charged are called ions.
A battery stores energy be separating the positively and negatively charged ions. This is hard to do because these ions don’t want to be separated. Letting the electrons on the negatively charged ions go where they want to go is exact how the battery provides power.
During charge/discharge cycles, the barrier that keeps these ions separated will become damaged. A damaged barrier is less effective and keeping these ions separated which means fewer atoms are in a charged state and this results in lower capacity.
The capacity of the battery is lower. There is a physical change in the battery that reduces the amount of charge that can be stored.
You will not spend less money or electricity to charge the battery. Technically a full charge costs less and use less electricity but at the same time, the range it provides is reduced.
On a long trip, you might need to charge one extra time, the cost each time you change will be less but the total charge cost will be the same.
If you drive it to work each day and charge it at home at night the amount of energy you add to the battery will be the same even if the battery has segregated. The difference might be it drops from 100% to 56% instead of 100% to 60% during the drive there and back.
Compare it to it you would put some rocks in the fuel tank of a car with an internal combustion engine and the rocks did not disrupt the function of the car. The result would be you can fit less fuel in the tank. Filling the tank cost less but it provides a lower driving range. The total fuel cost if you drive for a long time will be the same you just need to fill it up a bit more often during long trips.
Looking at a battery percentage is confusing, look at the energy storage instead. A 100kWh battery that degrades by 10% only stores 90kWh of energy.
If the car use 20kWh/100km you range have dropped from 100/20*100 = 500 km to 90/20*100= 450 km
The cost of filling an empty battery is lower because you only add 90kWh instead of 100kWh but at the same time you can derive 50km shorter.
Think of the kWh as a volume of fuel in a car with an internal combustion engine. We do not look at a trip usein 50% of the full tank of a car we look at it as it use a specific volume of fuel. Do the same with electric car and a specific amount of energy
The capacity is lowered. To understand this you need to think about the shape of the battery. While it might look like a thin pouch or cylinder, that’s not the actual shape. The actual shape is two large sheets of thin metal with a soft chemical in between them. These are folded up or rolled up to get the familiar macro shape.
The thin metal, much thinner than aluminum foil, is easy to tear. When the foil tears, it makes a part of the sheet “disconnected” from the rest and the electrodes connecting it to your gadget. Any power stored in that part of the sheet is unavailable for use. The soft chemical can be squeezed out of position, any temperature above 95˚F/35˚C during charging makes this much more common. Without the chemical layer, the battery can short, which is another cause of rips. In the worst case scenario a short can start a fire, lithium battery fires can be spectacular and dangerous. That’s why you can’t ship these batteries in the cargo part of an airplane.
>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.
Super simplified explanation;
Lets say you have 100 containers. You fill each of these contains with water every morning, and they’re used up by the next morning.
Now lets say one of the containers breaks, and (just for the sake of this explanation) you can’t replace that container without having to replace all the containers.
Now you can only hold 99 containers of water.
As a battery charges and discharges, it loses efficiency, tiny parts inside of the battery break down over charging cycles.
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