Questions on Adjusting OCP Offset and Defining Stoichiometry at Extreme SOC in LFP

PyBaMM Q&A
1

Dear PyBaMM Team,

I am working with an LFP (Lithium Iron Phosphate) battery model and would like some guidance on the following aspects related to the Open Circuit Voltage (OCP) profiles and stoichiometry:

  1. Adjusting the OCP Offset Between Electrodes: When plotting the OCP profile of an LFP battery with respect to the stoichiometry of both the positive and negative electrodes, how can we account for or adjust any offset between the two electrodes? Specifically, I am looking for guidance on how to address potential differences in the electrode potentials relative to the lithium concentration during charge and discharge.
  2. Determining Stoichiometry at 0% SOC and 100% SOC: How should we determine the stoichiometry of the electrodes at the extreme states of charge, i.e., at 0% SOC (fully discharged) and 100% SOC (fully charged)? Are there specific approaches or assumptions typically used to define these stoichiometric values in the context of LFP batteries?
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  1. The offset between electrodes (if I understood you correctly) is set by the initial concentration parameters. By adjusting them you can change the electrode balancing.

  2. The SoC estimation in PyBaMM follows the method presented in section 3.2.1 of this article: Towards better estimability of electrode-specific state of health: Decoding the cell expansion - ScienceDirect