From the pull-down menu Experiment Type, select the appropriate entry to simulate the charging or discharging of the battery cell or to set a charging profile. Here, a charging simulation is chosen. For the experiment types Charge Battery Cell and Discharge Battery Cell select the Boundary Conditions in Through Direction and the Start and End Condition. How to Set a Charging Profile is explained here.

The Boundary Conditions in Through Direction can be specified by a Charge Rate, a Current Density, by defining the Current in Ampere (A), or by defining the Cell Potential.

• With a Charge Rate defined, the applied current is related to the cell’s maximum capacity from 0% state of charge to 100% state of charge and is a measure of the duration of the battery charging. For example, a charge rate of 1 for a battery with capacity of 1 Ah means that the battery is charged completely in 1 hour with a constant current of 1 Ampere (A). This time is unrelated to the simulation time, but instead to the time that the charging process itself requires. A charge rate of 2 means that charging the same battery with a current of 2 Ampere takes ½ hour.

• Defining the Current Density instead means that the applied the applied current density (in A/m²) is defined directly.

• Defining the Current instead means that the applied current (in A) is defined directly.

• For the Charge Rate, Current, or Current Density Boundary Conditions, you can check Use Upper / Lower Cut-Off Voltage to set a first end condition to the simulation by limiting the voltage in a simulation. The voltage will not exceed this limit. I.e., if the cut-off voltage is reached, the charging will end.

• If Cell Potential is selected, the voltage is kept at a constant value during the simulation, and the current is a time-dependent value; the Cell Potential / (V) is the boundary condition. Select the Cut-Off Current as a first end condition to the simulation to be Charge Rate, Current Density or Current. For example, consider charging a battery at constant Cell Potential, and selecting a Cut-Off Charge Rate. The simulation starts with the entered SOC value and charges the battery at the provided constant cell potential, for example at 3.5 V. During the charging, the charge rate decreases with the increasing SOC. As soon as the charge rate is lower than the entered Cut-Off Charge Rate, the simulation stops.

The second Start and End Condition for the charging simulation can be defined in several ways:

• as minimum and maximum percentage of the state of charge (see State Of Charge (SOC)) of the whole cell (Minimum and Maximum Cell SOC)

• for the anode SOC and cathode SOC individually (Anode and Cathode SOCs),

• or, by selecting an initial .cap file from a previous BatteryDict simulation and defining a final SOC (Initial *.cap File and Final Cell SOC). This option is especially useful for simulating a charging or discharging process, starting from a non-equilibrium condition after a previous discharging or charging simulation.

Charging Profiles are a series of charging, discharging, and relaxation simulations that are performed sequentially for the same structure.

If Set a Charging Profile is selected as Experiment Type, the starting point for the first simulation can be defined

• as an equilibrium state of charge,

• or, by selecting a .cap file of a previous simulation.

The starting point for the following simulations, defined in the charging profile table, is always the final state of the previous one.

To define a charging profile, choose as many rows for the table as simulation steps desired. Select for each step, if the battery is charged, discharged, or if relaxation is simulated.

For charging or discharging, define the Type of Boundary Condition and the corresponding value, in the same way as for simple charging simulations. The same options for the boundary condition (Charge Rate, Current Density, Current, and Cell Potential) are available.

For charging or discharging, next, the first stopping criterion for the selected boundary condition (Stopping Criterion at Boundary) is chosen for each simulation step. The available options depend on the Type of Boundary Condition (BC).

• If Charge Rate, Current Density, or Current is selected as BC, only a cut-off Cell Potential is possible as stopping criterion.
• For Cell Potential as BC, the first Stopping Criterion can be chosen between a cut-off Charge Rate, Current Density, and Current.

Enter the Stopping BC Value for the first Stopping Criterion, for the second stopping criterion a stopping state-of-charge for the whole cell (Stopping Cell SOC / %) and for the (optional) thirst stopping criterion a Stopping Time. The computation ends for each simulation step, if the first one of the stopping criteria is reached. The next simulation step will continue from this state.

For relaxation, no boundary conditions need to be defined, only the stopping time as the only possible stopping criterion of the relaxation step. In a relaxation step, the return of the battery cell to an equilibrium state after charging or discharging is simulated. The solver settings, including the time step, are set by BatteryDict to optimize the simulation time required for the relaxation step.

Periodic or Symmetric boundary conditions can be selected for the Boundary Conditions in Tangential Directions.

For periodic boundary conditions, the structure is assumed to repeat periodically in Y- and Z-direction and for symmetric boundary conditions, the structure is mirrored in Y- and Z-direction and the Li+ ions and electrons are reflected at the boundary in Y- and Z-direction. The connected and unconnected parts of the active materials and electrolyte depend on the boundary conditions, so they are determined when the simulation begins.

You can set a third end condition to the charging simulation by checking Max. Simulated Time. The simulation ends if the charging process exceeds the Max. Simulated Time. Note that the Max. Simulated Time is not the time that the solver is given for its computation, but it is the time, the simulated battery is given for charging or discharging.

Max. Simulated Time Let us consider a battery that is charged from 20% state-of-charge to 70% state-of-charge at a charge rate of 1C. The battery takes 30 min to charge. If the Max. Simulated Time is set to 600 seconds (10 min), then in this example, the battery will only be charged from 20% to 36.67% state-of-charge.