Modeling Li-Ion Battery Cells

You can use the Li-Ion Battery Cell model to simulate the process of charging or discharging rechargeable Li-ion battery cells, or discharging disposable lithium battery cells.

The Li-Ion Battery Cell Model 3D-MSE approach models the 3D micro-structure of an electrode and predict its electrochemical reactions to determine the quality and performance of a cell design.

During the discharge process, lithium de-intercalates from the anode active material where it dissociates at the electrolyte into lithium cations (Li+) and an equal number of electrons.

Note	The double-precision version is required for modeling the transport of Lithium ions.

To model Li-Ion Battery Cells:

Start a double-precision version of Simcenter STAR-CCM+.
Create a new simulation.

When modeling Li-ion battery cells, it can be difficult to manipulate parts at the microscale level due to the precision of the CAD-based tools (1.0E-8m) in Simcenter STAR-CCM+. To avoid such issues, import parts or create 3D-CAD parts using the meter length scale initially, then you can scale the mesh at a later stage.

Import the geometry parts or create 3D-CAD parts that represent the microscale section of the Li-ion battery cell.

If you are importing parts, in the import dialog, make sure that you activate Create Part Contacts from Coincident Entities. Each Li-ion battery cell must contain at least the following parts:

an anode electrode
a cathode electrode
an electrolyte

If necessary, you can also include parts for anode and cathode collectors.

The anode and cathode electrodes can be represented in different ways, depending on the scenario that you are modeling. Choose one of the following options:

To obtain the most realistic results, you can import geometry that is created from a three-dimensional reconstruction of an electrode. You can use parts or meshes that are created from imaging technology such as x-ray, or focused ion-beam/scanning electron microscopy (FIB/SEM) imaging.
For a simplified representation of the irregular and complex structure of the active material, for each electrode you can create a simple solid structure of randomly distributed solid particles that form one part. The solid active material exists within the electrolyte. You can decrease the porosity by increasing the number of solid particles that are contained in the overall volume, or increase the porosity by decreasing the number of solid particles.
When you only want to model one electrode in detail, follow one of the previous options for this electrode, then use the lumped approach for the other electrode. Either electrode can be lumped, depending on what application you are interested in modeling. For example, if you are concerned with modeling discharge of graphite anodes, you can create a lumped cathode. However, if you want to model cathodic protection, you can create a lumped anode.
1. Approximate the lithium foil by a hexahedral block. The mesh for this block can be coarse.
2. For the Solid Electrolyte Interface (SEI), use an Electrode Equilibrium Potential that is linear and set the reference foil Electrode Equilibrium Potential $U_{eq} = 0$ as follows:
  - For Electrode Equilibrium Potential for y = 0, set the value to 0.
  - For Electrode Equilibrium Potential for y = 1, set the value to 0.
3. Deactivate Prevent Electrode Depletion.
4. Set the rate constant to a high value, for example 1.0E-3 kmol/m2 s.
  Typically, lumped electrodes are used when the behavior at that electrode is not of interest. Lumped electrodes are a crude approximation of the more detailed electrodes which contain active material dispersed through an electrolyte. The lumped electrode is only required to complete the circuit. Therefore, setting a high rate constant ensures that materials can easily pass across the interface at the lumped electrode and continue the flow of current.
5. To make sure that the resolved, non-foil electrode is capacity limiting, set Maximum Concentration in Electrode $c_{s, max}$ , to a high value, for example $c_{s, max}$ = 1E30.
If you want to model a disposable battery, create the cathode using the same process as in either of the first two options above. Then, for the anode, create a thin solid part to represent a foil of lithium metal.

Note

To obtain realistic results when you use simplified representations, it is important to make sure that the porosity of the active material in an electrode is represented accurately. You can determine the porosity from the ratio of the solid volume to the total volume. Li-Ion batteries with a high porosity (less solid volume and more electrolyte) have a high-power output since there is less resistivity in ionic conductive pathways which allows high currents to flow. However, Li-Ion batteries with a low porosity (more solid volume and less electrolyte) are better for storing a high energy density as energy is stored in the solid material.

If contacts do not exist between coincident parts, create part contacts or imprint parts.
See: Creating Part Contacts Manually or Imprinting Parts On Their Neighbors.
Assign parts to regions, make sure that Create Interfaces from Contacts is activated, and select the following options:
- Create a Region for Each Part
- Create a Boundary for Each Part Surface

Create physics continua to represent the regions.

The table below shows an example of how to allocate regions to physics continua:


Physics Continua	Regions
[Anode Electrode Continuum]	[Anode Electrode]
[Anode Collector Continuum]	[Anode Collector]
[Cathode Electrode Continuum]	[Cathode Electrode]
[Cathode Collector Continuum]	[Cathode Collector]
[Electrolyte Continuum]	[Anode Electrolyte]
	[Cathode Electrolyte]
	[Separator]

For each Physics Continuum, select the physics models.

The table below shows an example selection of physics models (in order) for each of the different continua:

Note	Auto-select recommended models is activated.


Group Box	Model
	[Anode Electrode Continuum]	[Anode Collector Continuum]	[Cathode Electrode Continuum]	[Cathode Collector Continuum]	[Electrolyte Continuum]
Time	Implicit Unsteady
Material	Solid				Liquid
Flow					Segregated Flow
Viscous Regime					Laminar
Equation of State	Constant Density
Space	Either, Three Dimensional or Two Dimensional
Optional Models	Electrochemistry				Electrochemistry
Electrochemistry	Li-Ion Battery Cell				Li-Ion Battery Cell
Optional Models	Li-Ion Concentration		Li-Ion Concentration		Li-Ion Concentration (selected automatically)
	Li-Ion Electric Potential				Li-Ion Electric Potential (selected automatically)
	Segregated Solid Energy
Energy					Segregated Fluid Temperature

Note	The Li-Ion Battery Cell Model is available only in implicit transient simulations. The Li-Ion Concentration model is not used for anode or cathode collectors as this model is designed to model the concentration of lithium in the active material and electrolytes only.

Set the required Material Properties for the Solid and Liquid models within each physics continuum.
Specific Liquid Material Properties:
- When using either the Li-Ion Electric Potential or Li-Ion Concentration model, you can specify liquid electrolyte material properties using predefined material property constants or tables which are stored in the materials database. Each table contains values for the material property at varying Li-ion/salt concentrations and temperatures of the electrolyte. Constant values are given for each material property at 30 °C and a molality of 1 mol/kg.
  1. Expand the Continua > Continuum > Models > Liquid > [Electrolyte] > Material Properties node.
  2. Depending on the case, select one of the following options:
    - When values of Temperature and Lithium/Salt Concentration do not vary much, use the predefined constant data:
      Multi-select the following nodes; Concentrated Solution Correction to Salt Diffusivity, Electrical Conductivity, Lithium/Salt Diffusivity, Non-Ideal Solution Correction to Salt Migration, and Density. Then in the Multiple Objects - Properties window, set Method to Constant.
    - For detailed setups in which the values of Temperature and Lithium/Salt Concentration vary significantly, use the predefined tabular data:
      Multi-select the following nodes; Concentrated Solution Correction to Salt Diffusivity, Electrical Conductivity, Lithium/Salt Diffusivity, and Non-Ideal Solution Correction to Salt Migration. Then in the Multiple Objects - Properties window, set Method to Table(T,c).
Set the boundary conditions. You cannot set independent boundary conditions for the liquid electrolyte phase. This phase has an interface with solid active electrodes. If the Li-Ion Electric Potential and Li-Ion Concentration models are activated in both regions, the SEI interfaces are created automatically. However, one region must be liquid and the other solid; SEI interfaces are not created for solid/solid and liquid/liquid interfaces.

If you set the Specific Electric Current or Electric Current Density boundary condition, you are explicitly specifying the electric current that is flowing across that boundary. For example, if you set a value of 1 A/m2, the normal component of the electric current density is set to a constant value of 1 A/m² along the entire boundary.

For the Electric Current boundary condition, you are specifying the total electric current that is flowing across the boundary. However, the profile of the specific electric current along the boundary is not necessarily constant. It is the integral value of the current across the boundary that is fixed at the specified value; the specific electric current can change as the solution develops.
1. Select the Regions > [Region] > Boundaries > [Boundary] > Physics Conditions > Electric Potential Specification node.
2. In the Properties window, set the Method property:
  - For a Neumann boundary condition:
    - If you know the total electric current, set Method to Electric Current.
      The electric current is defined in A. This boundary condition type specifies the total electric current through the boundary. Current entering the domain is a positive electric current. Current leaving the domain is a negative electric current.
    - If you know the electric current density, set Method to Specific Electric Current or Electric Current Density.
      The electric current density is defined in A/m². The total current through the boundary is the product of the electric current density with the area of the boundary. The Specific Electric Current is entered as a scalar profile, while the Electric Current Density is entered as a vector profile.
  - For a Dirichlet boundary condition:
    - If you know the electric potential, set Method to Electric Potential.
      The Electric Potential $φ$ is defined in V.
    - If you know the electric current density, set Method to Electric Current Density.
      The electric current density is defined in A/m².
3. Select the Regions > [Region] > Boundaries > [Boundary] > Physics Conditions > [Specific Electric Current, Electric Current, Electric Current Density, or Electric Potential] node and set the value.
To define the boundary conditions for the concentration:
1. Select the Regions > [Region] > Boundaries > [Boundary] > Physics Conditions > Lithium Wall Concentration Specification node.
  - To specify a Neumann boundary condition, set Method to Flux.
  - To specify a Dirichlet boundary condition, set Method to Concentration.
2. Select the Regions > [Region] > Boundaries > [Boundary] > Physics Conditions > [Lithium Concentration Flux or Lithium/Salt Concentration] node and set the value.
Define the properties of the Solid Electrolyte Interface. See Li-Ion Electric Potential Model Interface Settings.
Set the Initial Conditions. To determine the appropriate initial (or reinitialization) conditions for Lithium/Salt Concentration in both electrodes:
1. Create an initial setup with a constant Lithium/Salt Concentration of $c = c_{s, max} / 2$ as initial value in both electrode regions.
2. Optionally, select the Reports > [Li-Ion Cell 1] node, and set the SOC Step Increment expert property. For more information, see Li-Ion Cell.
  
  This expert property sets the resolution of the state table.
3. Run the Li-Ion cell Report.
  In the Output window, the state table gives the conditions for a cell at a given $S O C$ .
4. Use the value of Average Concentration+ at the required $S O C$ for the concentration at the cathode.
5. Use the value of Average Concentration- at the required $S O C$ for the concentration at the anode.
Set the Solver Parameters and Stopping Criteria.
See:
- Electric Potential Solver Reference
- Lithium/Salt Concentration Solver Properties
When modeling 3D-MSE battery cells, you are advised to set the Electric Potential model Solver Method to Hypre Linear Solver.
Prepare Scenes and Plots on which to visualize results.
For available field functions, see:
- Li-Ion Concentration Model Field Functions
- Li-Ion Electric Potential Model
Run the Simulation.
You can also create Li-ion cell reports after initializing the simulation.
1. Create a Li-Ion cell report.
2. Select the Reports > [Li Ion Cell 1] node and set the Li-Ion Cell Properties.
3. Optionally, set the Monitor Value to the quantity that is monitored when creating a monitor.

To practice setting up a Li-ion battery cell, try working through the Li-Ion Battery Cell Model: Cell Electrochemistry Analysis tutorial.