Initial Cell Charge Distribution
Use the Initial Cell Charge Distribution global node to define the initial cell voltage or cell state-of-charge (SOC) of a battery cell. When used together with a Current Distribution Initialization study step, the node will solve for the intercalated concentrations in the Porous Electrode and the Additional Porous Electrode Material nodes in order to comply with the given initial conditions.
The node also offers the possibility to balance the electrodes by calculating the electrode phase volume fractions.
The node only has an effect on the actual equations solved for when used in a Current Distribution Initialization study step. SOC and porosity variables will however be defined for all study steps. For more information on the functionality of this feature, see Initial Charge Distribution in the Battery Cell.
Use the Negative Electrode Selection and Positive Electrode Selection subnodes to select what domains of the battery model that correspond to the negative and positive electrodes, respectively. The node is only available in the Lithium-Ion Battery and Battery with Binary Electrolyte interfaces.
Battery Cell Parameters
Select an Initial battery cell setting — Initial cell voltage (the default) or Initial cell state-of-charge.
The entered Initial cell voltage Ecell,0 (SI unit: V) needs to be a valid value that can be physically achieved for the combination of state-of-charge windows and equilibrium potentials of the active materials of the two electrodes (as defined in the Porous Electrode and Porous Electrode Reaction node). The default is 3 V.
The Initial cell state-of-charge SOCcell,0 (dimensionless) should range between 0 and 1; 0 representing a fully discharged and 1 a completely charged cell. The default is 0.5.
The Battery cell capacity Qcell,0 (SI unit: C) is physically limited by the maximum amount of cyclable species in the selected electrode materials (as defined in the Porous Electrode node), and the model geometry (as defined in the Geometry node). A too high value in combination with a too small electrodes may result in intercalation concentrations higher that the maximum concentrations, or electrode porosities higher than one when defining the cell balancing in the next section.
Battery Cell Electrode balancing
Electrode balancing optimizes the amount of electrode material in each electrode with regards to the total capacity of the battery cell, and to ensure that the concentration of intercalated species in electrode material is maintained within the specified state-of-charge window during cycling.
The feature computes the electrode volume fraction variable for each of the electrodes, which may be used when defining the electrode volume fractions in the Porous Electrode nodes. The electrode balancing does not support models using Additional Porous Electrode Material nodes.
A geometrically larger electrode domain results in a lower electrode volume fraction, and an electrode with an active material with a relatively narrow SOC window and a low maximum concentration results in a high electrode volume fraction, and vice versa.
The Fraction of cyclable species loss after cell assembly fcycl,loss (dimensionless) and Fraction of hosted capacity excess in the negative electrode fhost,neg,ex (dimensionless) are properties that strongly impact the charge distribution in many battery cell chemistries. The default values are 0.08 and 0.20, respectively, and represent a typical case of a fresh lithium-battery cell with a 20% excess of carbon-based negative electrode, and where 8% of the cyclable lithium is lost due to irreversible process at cell assembly and initial “formation” cycling.
To balance the electrodes, enter in the Porous Matrix properties section of the Positive Porous Electrode nodes either <physics interface name>.epss_neg or physics interface name>.epss_pos (for example, batbe.epss_neg or liion.epss_pos) in the Electrode Volume Fraction text field, depending on the porous electrode being a negative or a positive electrode.