The Lumped Battery (lb) interface () found under the Electrochemistry > Battery Interfaces branch () offers a simplified (compared to, for instance, the Lithium-Ion Battery interface) approach to battery modeling by allowing for defining battery models based on a small set of lumped cell parameters. The interface is suitable to use when only limited information is available about the internal structure or design of the battery electrodes, or choice of materials.

Two entries that adds the Lumped Battery interface to the model tree are available in the Model Wizard. The Lumped Battery Model Wizard entry uses the Lumped cell model option by default, which defines contributions to cell voltage losses in the battery, stemming from ohmic resistances and (optionally) charge transfer and/or diffusion processes, instead of differentiating between the various processes in the negative and positive electrodes, and the electrolyte. The Lumped cell model solves for the battery state of charge as a dependent variable, and the open circuit voltage of the battery is defined as a function of the state of charge. If a concentration overpotential is included in the model and calculated based on diffusion in an idealized particle, the state of charge variable is solved for in an extra dimension, representing a generalized electrode particle (or electrolyte diffusion layer) wherein concentration overpotentials occur due to limited mass transport of a reacting species to the electrode-electrolyte interface, where the charge transfer reaction takes place.

The Lumped Battery, Two Electrodes Model Wizard entry uses the Two electrodes model option by default. Here the parameter set is extended to use lumped parameters for charge transfer and diffusion defined individually for the positive and negative electrodes. A Lumped Battery model defined using the Two electrodes option is also commonly referred to as a single-particle model in literature. The Two electrodes model solves for individual degrees of conversion dependent variables for the positive and negative electrode, and the open circuit voltage of the battery model is defined by the half cell equilibrium potential curves of the positive and negative electrode materials, as functions of the degree of conversion variables. Similar to the Lumped cell model, if concentration overpotentials (defined separately for the positive and negative electrode) are included in the model and calculated based on diffusion in an idealized particle, the respective positive or negative degree of conversion variable is solved for in an extra dimension, representing respectively a generalized positive or negative electrode particle.

The Lumped Battery interface with the Lumped cell model can be solved in a Global version, where the state of charge dependent variable and diffusion extra dimension are defined globally, or in a Local version (available in all space dimensions except 0D), where the variables are solved for locally in the same space dimension as the physics interface. The local version, which renders a significantly higher computational load, is suitable for modeling inhomogeneous cells where local differences in the model parameters (such as temperature dependent resistances) induce localized differences in the battery cell current density. One example could be cold start of a battery pack, where local currents will cause local heating with a positive feedback when the increased temperature raises the local electrolyte conductivity. The local model contains both global and local variables. Conversion between local and global variables are done by integrating over the total cell volume. The Lumped Battery interface with the Two electrodes model is always solved using global variables.

The Label is the default physics interface name.

The Name is used primarily as a scope prefix for variables defined by the physics interface. Refer to such physics interface variables in expressions using the pattern <name>.<variable_name>. In order to distinguish between variables belonging to different physics interfaces, the name string must be unique. Only letters, numbers, and underscores (_) are permitted in the Name field. The first character must be a letter.

The default Name (for the first physics interface in the model) is lb

Use the Operation mode setting to specify the load of the battery.

Use the Model setting to choose between a Lumped cell or a Two electrodes model.

The option to switch between a Global or Local definition of the dependent variables of the model is available only for the Lumped cell model in all space dimensions except 0D. The difference between the global and local model is described above.

For the Lumped cell model, the Initial battery cell capacity (C) specifies the initial battery capacity.

For the Two electrodes model, the Initial negative host capacity (C) and Initial positive host capacity (C) specify the respective electrode initial host capacities.

For the Lumped cell model, the Initial cell state of charge (1) specifies the state of charge of the battery when the simulation starts.

For the Two electrodes model option, the initial charge distribution can be defined by specifying either the Initial cell state of charge (1) or the Initial cell voltage (V). Additionally, the total charge inventory of the cell needs to be set. This can be done either based on the Positive electrode host capacity, the Negative electrode host capacity, or an Explicit value. It is also possible to enable Add formation loss to reduce the initial charge inventory, assuming that some charge inventory has been irreversibly lost prior to the start of the simulation. The formation loss can be set either to Fraction of negative host capacity, Fraction of positive host capacity, or an explicit Charge value.

This section is applicable to the Two electrodes model option. In this section, the Cell voltages at 0% and 100% SOC are defined. These voltages are used to connect the SOC of the battery cell to the individual electrode charge levels.

The Cell voltages at 0% and 100% SOC can be defined either From operational potential limits or User defined. For the From operational potential limits case, the settings of the Operational Potential Limits section in the Negative Equilibrium Potential and Positive Equilibrium Potential nodes are used to define the 0% and 100% SOC cell voltages.

This section is applicable to the Lumped cell model and the Global option. In this section, select either the Reference equilibrium potential and temperature derivative option or the Equilibrium potential and thermoneutral potential option. The appropriate inputs are thereby enabled in the Cell Equilibrium Potential node.

To display this section, click the Show More Options button () and select Advanced Physics Options.

Use Perturbation amplitude (A) to specify the perturbation on the applied battery current. This section is applicable only for Frequency-Domain Perturbation studies using the Galvanostatic operation mode.

A battery volume variable is used in order to calculate a battery heat source variable (lb.Qh, SI-unit: W/m3) from the lumped model. The heat source can typically be used for thermal simulations in combination with a Heat Transfer interface.

A Battery Volume (m3) setting is available in 0D.

In 1D, the selected domain length, in combination with the Cross-Sectional Area is used for calculating the volume.

In 2D, the selected domain area, in combination with the Out-of-Plane Thickness is used for calculating the volume.

To display this section, click the Show More Options button () and select Advanced Physics Options.

In this section you can set the checkbox Exclude heat source variable from Jacobian. The checkbox is selected by default in 3D and is not selected by default in other space dimensions. Note that this checkbox is relevant only when coupling to heat transfer interfaces. Excluding the heat source from the Jacobian may decrease the computation time.