Electrochemical Modelling of Na-MCl2 Battery Cells Based on an Expanded Approximation Method

Battery models are mathematical systems that aim to simulate real battery cell sufficiently accurately. Finding a comprise between complexity, computational effort and accuracy is thereby key. In particular, modelling sodium-nickel-chloride/iron-chloride cells (Na-NiCl2/FeCl2), as a promising alternative for stationary energy storage, bears some challenges. The literature shows a few interesting approaches, but in most of them the second active material (NiCl2 or FeCl2) or the entire discharging/charging cycle is not considered. In this work, an electrochemical and thermal model of Na-NiCl2/FeCl2 battery cells is presented. Based on an equivalent circuit approach combined with electrochemical calculations, the hybrid model provides information on the performance of the cell for charging and discharging with a constant current. By dividing the cathode space into segments, internal material and charge flows are predicted, allowing important insights into the internal cell processes. Besides a low calculation effort, the model also allows a flexible adaption of cathode composition and cell design, which makes it a promising tool for the development of single battery cells as well as battery modules and battery systems.