Modelling the effects of areal capacity on mass transport in liquid metal batteries

Abstract

Liquid metal batteries (LMBs) are formed from three molten layers, and the interaction of thermal, compositional and electromagnetic forces influences their performance and stability. The coupled behaviour of these forces in LMBs remains uncharacterised, so in this study, a three-layer numerical model was developed to investigate this interaction in lab-scale to grid-scale batteries; areal capacities 0.9–7.5 Ah/cm2. Thermal convection was modelled first, and Rayleigh-Bénard convection, a flow observed in the anode, only developed in batteries larger than current grid-scale batteries. Electro-vortex flow was introduced and found to suppress thermal convection in the anode and electrolyte layers. Thermally stratifying temperature gradients in the cathode had some effect on electro-vortex flow, but compositional effects from mass transport were dominant. Finally, a background magnetic field was used to induce swirl flow, and the coupled effects of this flow with thermal gradients was studied. Swirl flow also suppressed thermal convection, and stratifying temperature gradients had little effect on the flow; however, compositional gradients in the cathode decelerated the poloidal velocity of swirl flow during discharge. These results show that electromagnetic flows are dominant in LMBs, and mixing compositional gradients in the cathodes of large areal capacity batteries remains a challenge in the field.