[GeoDict 2023] How can I simulate charge rate dependent capacities?

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In an experiment, I observe capacities that depend on the charge rate, i.e. larger charge rates result in reduced capacity. How can I represent this observation in a BatteryDict simulation?


Roman Buchheit

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Let me pleaseanswer to this issue to show you how you can easily reflect the effect of different charging rates on the cell capacity in BatteryDict in GeoDict 2023.

The reached capacity during cell cycling is often defined by upper/lower cell voltages  in real experiments. These upper/lower cell voltages are reached during the discharge/charge of a cell. The limitation of cell voltages prevents damage of a cell, e.g. by lithium plating at very low cell voltages or electrolyte decomposition at very high cell voltages.
In GeoDict 2023, the cut-off voltages can be provided as a boundary condition to stop a constant current charging simulation.

As an example, let us consider the delithiation of a NMC622 cathode vs a lithium reservoir using the "Charge Half Cell" functionality of BatteryDict. The cell potential of the half cell will increase during delithiation of the NMC622, i.e. we want to provide an upper cut-off voltage to stop the simulation. This can be done in the "Experiment" tab in the Edit parameters window of charge half cell. Please toggle the checkbox at "Use Upper Cut-Off Voltage" and enter the desired cut-off voltage. With the settings provided below the simulation will stop either when the upper cut-off voltage of 4.3 V is reached or when the final Electrode SOC of 5% is reached.

You will see the effect when performing charging simulations with different C-rates: if you use higher C-rates/currents, the cut-off voltage might be reached at less transferred capacities. In the example, the cut-off potential of 4.3V was reached after a transferred charge of 0.423 µAh with the lowest current (2C), while larger currents reached the cut-off potential already after a transferred charge of 0.417 µAh (3C) and 0.402 µAh (4C).

For further details regarding the cut-off voltage settings, please refer to the current BatteryDict User Guide.
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