Simulation of Liquid Metal Batteries by Continuum Mechanics

Liquid metal batteries (LMB) are built as a stable density stratification of two liquid metals, separated by a likewise liquid salt. If the materials are correctly chosen, all three phases self-assemble (figure 1). During discharge, the anode metal will donate electrons, the ion will diffuse through the electrolyte layer and alloy there with the cathode metal.
The main advantage of LMBs is the very low price: low-cost raw materials together with a simple set-up and scalability make such cells an ideal stationary storage, which is highly needed for buffering fluctuating renewable energies. The liquid-liquid interfaces allow for optimal kinetics, i.e. for a fast response time and current densities up to 10 A/cm2. Furthermore, they avoid micro-degradation - as known from solid cells - and allow for potentially very high life-times.
Safety will play a major role in the construction of such cells – especially due to the high amount of liquid and reactive metals. In that context, a short circuit of the thin electrolyte layer should be avoided. In large liquid metal batteries with diameters in the order of several decimetres, even the discharging current itself may lead to a fluid flow, able to short-circuit the battery.

We will present numerical simulations of the fluid flow in LMBs and estimate their relevance for real cells. The numerical solvers combining heat transfer, fluid- and electrodynamics with the volume of fluid method are implemented in the open source library OpenFOAM. Reviewed phenomena include thermal convection, electro-vortex flow, the Tayler-instability as well as metal pad rolling, which is well known from aluminium reduction cells.