If several active materials are used in an electrode, an additional check controls that the value ranges of the open-circuit potential (OCV) curves of all materials overlap. Otherwise, there is no well-defined equilibrium state of the battery cell, which is the starting point for the simulation.

OCVs are the driving force in a battery that make lithium ions flow from materials with low OCV to materials with high OCV. If a battery is used in an electrical device and the two electrodes are conductively connected, ions flow from the negative electrode (low OCV) to the positive electrode (high OCV). The charging process requires an additional external driving force (the charging device) to cause ions to flow in the opposite direction.

If one of the electrodes is composed of several active materials, the OCV-curves of the active materials differ (at least a bit). Since the active materials in an electrode are conductively connected, there will be a driving force that will move ions from particles with low OCV to particles with high OCV. This process continues until all active materials within the electrode have the same OCV value and the electrode is in equilibrium.

In BatteryDict, the Cell-SOC or the electrode-SOC determine the initial amount of charge (i.e. lithium ions) stored in the electrode. Before starting the simulation, the solver will try to distribute this initial amount of charge between the different active materials of an electrode. This is done in such a way that the electrode is in equilibrium, i.e., that the OCVs are equal. This can only be achieved if the OCV curves of the active materials share common values.