Setting Boundary and Interface Conditions

Define the boundary conditions at the free surfaces of the two current collectors.

To simulate an approximate discharge current of 10 A/m2 across the cell segment, you define the current density at the anode collector, and a zero electric potential at the end of the cathode collector.



The discharge process is an electrochemical process: under an applied electric current, the lithium that is inserted in the anode active material is dissociated into a Li+ ion and an electron. The Li+ ion then migrates through the separator and is inserted into the cathode active material. Hence, the concentration of Li+ ion decreases on the anode side and increases on the cathode side over time.

You specify the current density, in A/m2, at the anode since both the current and the anode areas are known. To allow a null net flux, you set the electrical potential at the outlet to 0 V.

To set the boundary and interface conditions:

  1. Expand the Regions > Anode Collector > Boundaries > Free Surface node.
  2. Select the Physics Conditions > Electric Potential Specification node and set Method to Specific Electric Current.
  3. Select the Physics Values > Specific Electric Current node and set Value to 10 A/m^2.
  4. Expand the Regions > Cathode Collector > Boundaries > Free Surface node.
  5. Select the Physics Conditions > Electric Potential Specification node and set Method to Electric Potential.

    Leave the default 0.0 V for the corresponding value of electric potential.

At the SEI, the Butler-Volmer relationship is used to compute the normal component of the electric current density at the SEI. The equilibrium potential of the active material term varies with the relative concentration in the electrode. Two tables are provided for you to use in the positive and negative electrodes.

  1. Multi-select the Interfaces > Anode AM/Anode Electrolyte node and the Anode AM/Separator node.
  2. Right-click any selected node and select Edit....
    The Multiple Objects dialog appears.
  3. Expand the Physics Values > Butler-Volmer Relationship Parameters node and set Electrode Equilibrium Potential to Tabular.

    The Tabular Electrode Equilibrium Potential node appears.

  4. Expand the Tabular Electrode Equilibrium Potential node:

    • Set Table to UeqNeg.

    • Set Relative Concentration in Electrode (y) to y.

    • Set Electrode Equilibrium Potential to - Ueq.

  5. Click Close.
  6. Repeat the interface condition procedure for the Cathode AM/Cathode Electrolyte and Cathode AM/Separator interfaces, but set Table to UeqPos and Electrode Equilibrium Potential to Ueq.