Competing forces in liquid metal electrodes and batteries

Abstract

Liquid metal batteries are proposed for low-cost grid scale energy storage. During their operation, solid intermetallic phases often form in the cathode and are known to limit the capacity of the cell. Fluid flow in the liquid electrodes can enhance mass transfer and reduce the formation of localized intermetallics, and fluid flow can be promoted by careful choice of the locations and topology of a battery's electrical connections. In this context we study four phenomena that drive flow: Rayleigh-B\'enard convection, internally heated convection, electro-vortex flow, and swirl flow, in both experiment and simulation. In experiments, we use ultrasound Doppler velocimetry (UDV) to measure the flow in a eutectic PbBi electrode at 160{\deg}C and subject to all four phenomena. In numerical simulations, we isolate the phenomena and simulate each separately using OpenFOAM. Comparing simulated velocities to experiments via a UDV beam model, we find that all four phenomena can enhance mass transfer in LMBs. We explain the flow direction, describe how the phenomena interact, and propose dimensionless numbers for estimating their mutual relevance. A brief discussion of electrical connections summarizes the engineering implications of our work

Modeling discontinuous potential distributions using the finite volume method, and application to liquid metal batteries

“…Specifically, we would like to extend the model by convection [18,19], heat transfer [73,77] and electrode kinetics.…”

Thermally driven convection in Li||Bi liquid metal batteries

“…Several studies have shown that fluid motion can be triggered by magnetohydrodynamic effects, i.e., the interaction of a magnetic field (either a background field or the field caused by the battery current) with the cell current. This includes the Tayler instability [11][12][13][14][15][16], electro-vortex flows [17][18][19][20][21] as well as interface instabilities [22][23][24][25][26][27]. While the Tayler instability will get substantial only for large system (in the order of meters) [14], electro-vortex flow will appear already in small cells [19].…”

Electromagnetically driven convection suitable for mass transfer enhancement in liquid metal batteries

“…5b). The appearance of such azimuthal swirl flow is well known from experiments [43,85,103] and can be easily explained. Radial cell currents and a vertical magnetic background field lead to azimuthal Lorentz forces [87,92,103].…”

“…with t, u, p, ν, ρ, µ 0 , r and dV denoting the time, the velocity, the pressure, the kinematic viscosity, the density, the vacuum permeability, the coordinate and the differential volume, respectively. The fluid mesh has at least 200 cells on the diameter, which is fine enough according to [43].…”

“…The relevance of EVF for LMBs is outlined by Ashour et al [43]. It should also be mentioned that other flow phenomena like the Tayler instability [48][49][50][51][52][53][54][55][56], Rayleigh-Bénard convection [57,58] or interface instabilities [59][60][61][62][63] may enhance mass transfer in LMBs, as well.…”