Liquid metal batteries

Liquid metal batteries (LMBs) are fascinating electrochemical cells. Built as a stable density stratification of two liquid metals separated by a molten salt electrolyte, such cells offer cheap stationary energy storage and a long life time. Due to the totally liquid interior of these cells, fluid flow is of paramount importance for the safe operation of LMBs. As the highly resistive electrolyte needs to be as thin as possible, a strong fluid flow might easily wipe it away and short circuit the cell. Aside from that, a slight flow might be highly beneficial. When discharging a Li-Bi LMB, Li will cross the electrolyte layer and alloy into Bi. As this process is diffusion-controlled, a Li-rich layer will build up on top of the positive electrode. A mild flow might equalize the alloy, thus reducing concentration polarization and improving the cell's efficiency.

The talk will first explain the set-up and operation of liquid metal batteries. Afterwards, different possible flow mechanisms in LMBs will be presented and discussed. These will include thermally driven Rayleigh-Benard convection, solutal convection, pinch effects, interface instabilities, the Tayler instability and electro-vortex flow. Besides of the flow simulation, the modeling of the electric potential distribution, the current density and magnetic fields will be presented. Special attention will be paid to the implementation of the solvers in OpenFOAM, as well as the description of specialized discretisation schemes, which are necessary e.g. for computing the current density. Finally, it will be shown how different flows in the battery effect the cell voltage, and the integrity of the three layers.