The Lumped Battery Interface

The interface (

), found under the branch (

) offers a simplified (compared to, for instance, the Lithium-Ion Battery or the Single Particle Battery interface) approach to battery modeling.

Instead of differentiating between the various processes in the negative and positive electrodes, and the electrolyte, the Lumped Battery interface makes use of a small set of lumped parameters for adding contributions for the sum of all voltage losses in the battery, stemming from ohmic resistances and (optionally) charge transfer and/or diffusion processes. The applicability of the lumped approach depends on various internal battery parameters such as the combination of electrode and electrolyte materials, porosities and layer thicknesses, and the electrode-electrolyte chemistry, in relation to the current load.

Due to the limited set of parameters needed, the interface is suitable when only little information is available about the internal structure, or chemistry, of a battery. Heat sources are calculated automatically by the physics interface and can be used together with a Heat Transfer interface for thermal simulations.

The Lumped Battery interface is based on a similar set of equations as The Single Particle Battery Interface, with additional simplifications based on the assumption that the activation and concentration overpotentials can be attributed to one electrode only.

The interface solves for the battery state-of-charge as a dependent variable. If concentration overpotentials are 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 model is either solved in a global version, where the soc dependent variable and diffusion extra dimension are defined globally, or in a local version (available in 1D, 2D, and 3D), 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.

	Parameter Estimation of a Time-Dependent Lumped Battery Model: Application Library path Battery_Design_Module/Batteries,_Lithium-Ion/li_battery_1d

The is the default physics interface name.

The 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 field. The first character must be a letter.

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

This section is available in 1D, 2D and 3D. The domain selection of the interface is used to calculate the battery volume.

Use the setting to specify the load of the battery.

lets you specify the (A). This can be used to specify the battery current load. (The expression may be time-dependent using the character t for time.). mode lets you specify the settings that are required to apply a charge-discharge cycle, including constant current, constant voltage and rest periods. allows for specifying the (V) and allows for specifying the (W). lets you connect to the Electrical Circuits interface.

The (C) specifies the battery capacity.

The (1) specifies the state-of-charge of the battery when the simulation starts.

Use the setting (available in 1D, 2D and 3D) to switch between a or definition of the dependent variables of the model. The difference between the global and local model is described above.

To display this section, click the button (

) and select .

Use (A) to specify the perturbation on the applied battery current. This section is applicable only for frequency domain, perturbation studies using the 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 may typically be used for thermal simulations in combination with a Heat Transfer interface.

A (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.

In 3D, the battery volume equals the volume of the selected domain.

To display this section, click the button (

) and select .

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