Competing forces in liquid metal electrodes and batteries

TL;DR

This study investigates four fluid flow phenomena in liquid metal batteries, demonstrating through experiments and simulations that they can enhance mass transfer and potentially improve battery performance by reducing intermetallic formation.

Contribution

The paper identifies and analyzes four flow phenomena in liquid metal batteries, providing experimental measurements and simulation insights into their effects on mass transfer and battery efficiency.

Findings

All four phenomena can enhance mass transfer in liquid metal batteries.

Experimental velocities agree with simulations when modeled with a UDV beam model.

Flow directions and interactions are explained, with dimensionless numbers proposed for relevance estimation.

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.