Numerical Study of Species Distribution and Overpotentials in Liquid Metal Batteries

The liquid metal battery (LMB) technology is highly promising for grid scale stationary energy storage. Those batteries consist of two liquid electrodes and a liquid or solid state electrolyte. Due to the possible usage of earth-abundant and inexpensive materials, LMBs are sustainable and eco-friendly. The LMBs in the present study contain a molten salt liquid electrolyte. Since the batteries are fully liquid, fluid flow needs to be considered additionally to electrochemistry and electromagnetic fields. For numerical investigations, coupling of the corresponding fundamental equations as well as the different regions in the battery is needed, which is highly challenging. Besides multiple fluid flow phenomena that are affecting the battery performance positively as well as negatively, species transport in the electrolyte and the cathode has an influence on the cell potential as well.
In the presented talk, a quasi-one-dimensional method to calculate the ionic species distribution and the corresponding overpotentials in a LMB is presented. Since these phenomena are – to the best knowledge of the authors – rarely investigated, fluid flow is neglected for simplicity. The method is based on a simulation that solves current density and potential distribution in the whole battery. This requires modeling of the electrochemical double layer as well as multi-field coupling. Hereby, the finite volume method (FVM) is used and the simulations are performed using the open source tool OpenFOAM. Application cases are Li||Bi and Na||Zn cells (see Figure 1), having slightly differing working concepts. Li||Bi batteries are already investigated to a large extend and most material properties are readily available. Therefore, a validation study of the numerical solver is performed with these LMBs. On the other hand, Na||Zn batteries are even more sustainable and eco-friendly. The authors contribute, among others, to the development of the latter within the European Union’s Horizon 2020 project SOLSTICE.