## 4 Conclusions  
A model for predicting the electrochemical and thermal behaviour of _Na-MCl\({}_{2}\)_ cells based on a hybrid approach was presented. The model uses a resistor network consisting of Ohmic and electrochemical resistances. Based on Orchard and Weaving Orchard and Weaving (2015), the cathode compartment is divided into several segments, allowing the spatial resolution of the cell processes during charging and discharging. Compared to previously presented electrochemical modelling approaches, the developed model structure offers the advantages of a reduced complexity and consequently a lower computational effort, while representing the relevant cell parameters.  
First, the charge and discharge curves of the model were validated. A good prediction of the typical voltage plateaus were found, although certain discrepancies in the voltage values compared to the experimental data appear. Besides the impact of side reactions, which were not considered in the model, the unknown composition and simplified shape of the commercial validation cell has been identified as one of the reasons for these deviations. Secondly, the model was used to predict the discharge behaviour in a C-rate range of 1/2C to 1/24C as well as the hysteresis effect of the _Na-MCl\({}_{2}\)_ cell. Finally, the progress of the reaction front was monitored over a discharge cycle, in addition to the active material concentration distribution and the exchange current density distribution. Thus, the model represents a development tool for the target-orientated optimization of cell composition as well as the geometry that can be used to characterize cells in advance at reduced cost. It provides the necessary input parameters for module and system development as well as for transferring to future applications in large capacity storage. To cover the full application scenario, a further extension of the model will be necessary with regards to the relaxation processes. In this way, the cell response on current pulses and real load profiles could be determined. Nevertheless, besides model development, this requires additional experimen  
Figure 8: Results of the thermal model. (**a**) Overall heat generation of the reaction volume in one discharging cycle. (**b**) Contribution of the different heat generation terms. (**c**) Heat generation in a single segment (#50) over one discharging cycle with 1/8C.  
tal and analytical work to understand all the relevant electrochemical mechanisms in the cell [35]. Recent investigations have shown that high operation temperatures accelerate [PERSON] ripping of the cathode particles and therefore promote ageing of the cell [36]. Further study of particle properties and micro-scale processes representing such ageing phenomena would enable the presented model to cover the entire lifetime of _Na-MC12_ cells already in the development stage.  
Conceptualization, N.B., F.P., C.S.G., M.R., L.N. and S.Z.; methodology, N.B., C.S.G. and M.R.; software, N.B., F.P. and C.S.G.; validation, N.B.; formal analysis, N.B. and F.P.; investigation, N.B.; resources, S.Z. and A.M.; data curation, N.B.; writing--original draft preparation, N.B. and F.P.; writing--review and editing, N.B., F.P., M.R., L.N. and S.Z.; visualization, N.B. and F.P.; supervision, S.Z. and A.M.; project administration, S.Z. and A.M.; funding acquisition, S.Z. and A.M. All authors have read and agreed to the published version of the manuscript.  
This research was promoted by the Fraunhofer Project Center for Energy Storage and Systems ZESS and funded by the \"Niedersachsische Vorab\", support code 11-76251-99-2/17 (ZN3402).  
No new data were created or analyzed in this study. Data sharing is not applicable to this article.  
The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.