What is the formal definition of capacity fade?

Question

https://www.ipaceforums.co.uk/threads/capacity-fade-vs-power-fade.6794/

According to this post capacity fade is defined as the percentage of total capacity left. So I'm assuming it would be calculated like:

(current capacity/original capacity)*100

with the current capacity reducing with use of the battery.

However when comparing it with a capacity fade over time graph:

https://www.researchgate.net/publication/284655052_Degradation_Behaviour_of_Lithium-Ion_Batteries_based_on_Field_Measured_Frequency_Regulation_Mission_Profile

The % capacity fade is actually increasing over time? Shouldn't we expect this value to decrease over time as the current capacity in the formula decreases?

So I'm thinking that the definition used in the first post is different to the definition of what researchers consider capacity fade. What is the actual formula for capacity fade?

Answer 1

Different people would give these things different names most likely.

Looking at the graph the blue curves they are the percentage amount of capacity that's been lost with time, so the loss of capacity has to increase (more lost) the only way to make it decrease is to charge the battery.

Using different terminology you could write:

percentage capacity lost = 100 - (100 x capacity now/capacity originally) so the blue curve is the percentage capacity lost against time.

so I think percentage capacity fade = 100 - (100 x capacity now/capacity originally).

As for their definition "According to this post capacity fade is defined as the percentage of total capacity left" that's wrong.

Perhaps they should have written "capacity fade is defined as the percentage of total capacity lost" this statement agrees with the blue curves.

I don't know what the percentage capacity fade correction factor is.