## 1 Introduction
Another advantage of the _Na-MCl\({}_{2}\)_ technology is the high cycle life capability ([PERSON] et al., 2018), which makes it even more suitable for  
Figure 1: Reaction scheme during _NiCl\({}_{2}\)_ and _FeCl\({}_{2}\)_ reduction inside the cathode space, RF (reaction front). long-term use cases. Despite these advantages, major gaps between the ongoing research and the industrial relevance and applications still need to be overcome. Here, modelling can be a powerful tool for resource-efficient development. Within the field of _Ni-MCl\({}_{2}\)_ cells, models can help to improve cell performance by optimizing the cathode formulation or dimensioning. Electrochemical models of _Na-MCl\({}_{2}\)_ cells documented in the literature date back to the 1990s. Table 1 shows a detailed literature overview of mathematical/chemical model approaches. These models were analysed by their operational scenario, used cell chemistry and considered physical processes, e.g., heat formation. [PERSON] and [PERSON] [11] developed a mathematical model focusing on the porous cathode using the theory of transport processes inside binary molten salts by [PERSON] and [PERSON] [12]. The cell model implemented iron chloride as a single active material and no experimental work was performed to validate the numerical outcome. Further developments of this work, such as the one by [PERSON] and [PERSON] [13], take the solubility of \(FeCl_{2}\) into consideration, which was assumed to be constant by [PERSON] and [PERSON]. Another approach based on the work of [PERSON] and [PERSON] was performed by [PERSON] [14]. By extending the work to a 2D simulation, [PERSON] also investigated the thermal behaviour of the cell, considering both the active materials \(NiCl_{2}\) and \(FeCl_{2}\). Additionally, he was able to reduce the complexity of [PERSON] et al. 's assumptions, while retaining comparability to the experimental data. An even more straightforward approach was presented by [PERSON] and [PERSON] [15]. Their equivalent circuit model (EC model) divides the cathode compartment into segments of equal size. By using a combination of Ohm's law and electrochemical kinetics, the electrical behaviour and material balances for each segment is calculated. The simple procedure and cell division ensures a small number of equations resulting in a short calculation time, while a good agreement with the experimental data was achieved. However, [PERSON] and [PERSON]'s work is not intended for modern _Na-MCl\({}_{2}\)_ cells. Besides the consideration of a single active species (_Na-FeCl\({}_{2}\)_), the model represents the discharging process but not the entire cycle, including charging. Furthermore, heat generation is not included, which needs to be taken into account for battery system designs. Moreover, a planar cell design is considered. In summary, the work of [PERSON] and [PERSON] shows that the combination of EC models and electrochemical mathematical laws can be a powerful tool for the straightforward, model-based development of battery cells. In recent studies, this approach has already been applied successfully in the field of lithium-ion batteries, albeit in a more complex structure [16; 17; 18].