Investigating the interplay of heat and mass transport in a three-layer liquid metal battery model

Thermal and solutal convection effects have been proven to have a significant impact in liquid metal batteries (LMBs) with potentially beneficial but eventually detrimental effects on their operation. LMBs are likely to be good candidates for solving the 21st century challenge of storing electrical energy on a large scale in order to ensure the stability of electrical grids in the future, which will consist of an increasing amount of renewable energies. With their fully liquid interior, they feature numerous phenomena of fluid dynamics, which are studied in order to adjust the battery’s design. Among them are convective phenomena, which play a role when density gradients form due to heating or compositional variations. The typical LMB consists of three segregated layers featuring different characteristics. Thermal convection typically occurs in the negative electrode and the electrolyte, while solutal convection is unique in the positive electrode, where it occurs during charge of the battery. Previous numerical studies observed that thermal convection is dominant either in the negative electrode or in the electrolyte, which depends strongly on the layers’ thicknesses. Coupling between the interfaces has been observed, but was not yet studied in-depth. Effects of solutal convection have been studied on the isolated positive electrode only and could be associated with substantial flow.
We performed numerical studies to examine the interfacial coupling of the two types of convection in a three-layer model. Therefore we made use of an OpenFOAM solver specifically developed for this problem. The solver was first validated by performing a grid independence study and comparing the results to previous solutions. A configuration was then studied, where significant flow evolves due to both thermal and solutal convection in all three regions. We observed chaotic flow patterns, which were strongly affected by the interfacial coupling. As a result, the flow phenomena in the electrolyte are highly irregular, as it is affected from the other layers both at its top and bottom interfaces. We suspect the behaviour to be highly dependent on the exact configuration of the battery and therefore suggest that these phenomena are studied more extensively in the future.