Deg Modes don't make sense

General
1

Hi,

I have run some degradation sims and would like to plot the loss in capacity [Ah] for each degradation mode (LLI, LAM_NE, LAM_PE) as the cell ages.

Example_deg_mode
Example_deg_mode744×610 25.6 KB

I am aware that the deg. modes are available in [%] decrease (increase) but I would like to plot their absolute effect on the battery in Ah. The other available output channels are:

"Cyclable lithium capacity [A.h]",
"Negative electrode capacity [A.h]",
"Positive electrode capacity [A.h]",
"Capacity [A.h]",

But these do not add up correctly, i.e. the change in LAM and LLI combined does not equal change in capacity.

Could anyone help me on how I can extract information on how much capacity decrease (Ah), each degradation mode is responsible for?

2

Below is the change in each deg. mode as well as the change in capacity. The change in capacity is smaller than the cumulative change in capacity due to the deg. modes.

Delta_1
Delta_1640×480 22.6 KB

3

I am also confused as to why the cyclable lithium content does not constrain the capacity of the cell.

Deg_modes_1
Deg_modes_11000×600 23.7 KB

4

“Cell capacity” is a function of cyclable lithium inventory, electrode capacities, but it’s not just adding up the losses. See the Birkl et al to learn more about degradation modes.

In general the “theoretical capacity” can be calculated from cyclable lithium, electrode capacities, open-circuit potentials, and voltage limits by solving a system of algebraic equations given in the Birkl paper. The dynamic capacity (e.g. “1C capacity”) also depends on the internal resistance due to kinetics, diffusion, etc and can only be obtained by actually running the test (on a real cell or in simulation)

1 Like
5

Thank you @valentinsulzer for the response . I will have a look at the paper!

To conclude this discussion, is it safe to say that there is no way of extracting data from the simuation results to populate the first plot - Cap. loss vs Cycles (for LAM and LLI)?

6

Hi there, Are you extracting cell capacity from the output variable of “Discharge Capacity [A.h]” or following some other method of subtracting the losses from nominal cell capacity?