The Lead-Acid Battery Interface

The interface (

), found under the branch (

) when adding a physics interface, is used to compute the potential and current distributions in a lead-acid battery.

Ohm’s law is used to describe the charge transport in the electrodes, whereas concentrated electrolyte theory is used to describe charge and mass transport in the electrolyte phase. Mass balances for the porosities in the porous electrode domains account for changes in state-of-charge.

Different combinations of four dependent variables are valid and solved in different domains. The four dependent variables are:

•

ε, porosity (volume fraction of liquid electrolyte) in the Negative Porous Electrode and Positive Porous Electrode nodes.

A lead-acid cell typically consists of five parts: a positive porous electrode (PbO2), a reservoir of electrolyte, a porous separator, a negative porous electrode (Pb), and two electrodes in contact with the positive porous electrode and negative porous electrode, respectively.

When this physics interface is added, these default nodes are also added to the — , , , and . Then, from the toolbar, add other nodes that implement, for example, and nonporous , and boundary conditions. You can also right-click to select physics features from the context menu

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 leadbat.

	Exclude domains that do not conduct current.

See Out-of-Plane Thickness.

See Cross-Sectional Area.

The settings for the and determine how the electrolyte velocity is calculated in the model. The default settings correspond to lead acid battery using sulphuric acid as electrolyte.

The Physics vs. Materials Reference Electrode Potential setting on the physics interface node can be used to combine material library data for current densities and equilibrium potentials with an arbitrary reference electrode scale in the physics. The setting affects the electrode potentials used for model input into the materials node, as well as all equilibrium potential values output from the materials node.

Note that the setting will only impact how potentials are interpreted in communication between the physics and the Materials node. If the From material option is not in use for equilibrium potentials or electrode kinetics, the setting has no impact.

This section is available when the is selected in the dialog box shown when the button (

) is clicked.

This physics interface defines the following dependent variables (fields): , , , and . The names can be changed but the names of fields and dependent variables must be unique within a model.