Discrepancy in Discharge Capacity Between Chen2020 and Mohtat2020 Parameter Sets Despite Aligned Key Parameters

PyBaMM Q&A Parameters
1

Hello PyBaMM community,

I’ve been conducting simulations using both the Chen2020 and Mohtat2020 parameter sets. To ensure consistency, I’ve aligned several key parameters across both sets, including:

  • Maximum and initial concentrations in both negative and positive electrodes
  • Nominal cell capacity
  • Electrode dimensions (height, width, thickness)
  • Current collector thicknesses
  • Electrode and Separator porosity
  • Initial electrolyte concentration
  • Electrode densities

Additionally, I’ve assigned the same open-circuit voltage (OCV) interpolation plots to both the positive and negative electrodes.

Despite these efforts, I’m observing different discharge capacities between the two simulations. I’m seeking insights into potential reasons for this discrepancy. Specifically:

  1. Parameter Dependencies: Could there be underlying parameters or dependencies within the Chen2020 and Mohtat2020 sets that I’m overlooking, which might influence the discharge capacity?

  2. Model Initialization: Are there differences in how PyBaMM initializes models with these parameter sets that could lead to varying results?

  3. Best Practices: What are the recommended practices for ensuring consistency when comparing simulations across different parameter sets in PyBaMM?

Any guidance or suggestions would be greatly appreciated.

Thank you!

1 Like
2

Hi everyone,

Just wanted to follow up on my original question in case anyone else encounters a similar issue in the future.

After some investigation, I discovered that the discrepancy in discharge capacity between the Chen2020 and Mohtat2020 parameter sets—despite aligning several key parameters—was due to how porosity and active material volume fraction are handled in PyBaMM.

Specifically, both:

  • "Negative/Positive electrode porosity"
  • "Negative/Positive electrode active material volume fraction"

are independent parameters in PyBaMM and not derived from one another. This means that even if the porosity is the same across both parameter sets, differing active material volume fractions can significantly impact the effective capacity (since capacity is directly influenced by the amount of active material).

To ensure consistent comparisons between parameter sets, it’s important to:

  • Explicitly set both the porosity and the active material volume fraction to the same values across simulations.
  • Be mindful that PyBaMM does not automatically enforce physical consistency between these parameters, so this must be done manually.

Hope this helps others who are trying to compare different parameter sets!