SOC and Initial Charge Distribution
This global node is activated by enabling Define cell state of charge and initial charge inventory on the interface top node. The node is only available in the Lithium-Ion Battery and Battery with Binary Electrolyte interfaces.
The node can be used to define and compute various dynamic global cell variables such as the cell capacity, state of charge (SOC) and state of health (SOH), and it also allows for specifying the initial SOC of the battery in terms of either cell voltage, cell SOC, or the individual positive and negative electrode potentials, or charge inventories.
The following variables are defined and made available for global evaluation by the node (where xxx refers to the interface name, for instance liion, or batbe):
Table 3-1: Variables for SOC and Initial Charge Distribution.
Variable Name
Unit
Description
xxx.SOC_cell
dimensionless
Cell state of charge
xxx.SOH_cell
dimensionless
Cell state of health
xxx.I_1C_cell
A
1C cell current
xxx.Cap_cell
C (Ah)
Cell capacity
The node has two child nodes: Negative Electrode Domain Selection (or Negative Electrode Boundary Selection) and the Positive Electrode Domain Selection (or Positive Electrode Boundary Selection), depending on the Electrode Selection Type, which can be set to either Domain or Boundary. It is required that the Domain Selection (or Boundary Selection) of these child nodes coincide with the selection of one or several active Particle Intercalation nodes (child nodes either to Porous Electrode or Additional Porous Electrode Material for domain selection, or to Thin Porous Electrode for boundary selection) in the model.
The Cell Type can be set to either Full cell or Half cell. For Full cell, both the negative and positive child nodes are active. For Half cell, only the positive child node is active, and the (fixed) negative electrode potential is instead defined by the Reference (counter) electrode equilibrium potential setting.
In the State-of-Charge Definition 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 charge levels of the Particle Intercalation nodes.
The cell voltages at 0% and 100% SOC may be either defined From operational potential limits or User defined. For the From operational potential limits case, the settings of the Operational Potential Limits section in the Particle Intercalation nodes, in combination with the Negative Electrode Domain Selection (or Negative Electrode Boundary Selection) and Positive Electrode Domain Selection (or Positive Electrode Boundary Selection), are used to define the 0% and 100% SOC cell voltages.
The Initial Cell Charge Distribution section defines the initial concentration levels of all Particle Intercalation nodes included in the Negative Electrode Domain Selection (or Negative Electrode Boundary Selection) and Positive Electrode Domain Selection (or Positive Electrode Boundary Selection). The initial charge distribution may be defined be either Cell state of charge, a Cell Voltage, Electrode Potential, or Electrode Charge Inventory.
For a Full cell, when specifying a Cell state of charge or a Cell Voltage also the total charge inventory of the cell needs to be set. This may 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..
By default the initial charge inventory is based on the Positive electrode host capacity, with an added formation loss set to Fraction of negative host capacity. This corresponds to, for instance, the common case of a lithium-ion battery, where all cyclable lithium after manufacturing stems from the positive electrode material (such as LCO, NCA, NMC etc). A small fraction of inventory is irreversibly lost during initial cycling due to the formation of the solid-electrolyte interphase (SEI) at the surface of negative graphite electrode particles.
•
Cell Capacity and State of Charge
•
Defining Initial Cell Charge Distributions Based on Cell Voltage or Cell State of Charge