Metal pad roll instability in liquid metal batteries

TL;DR

This paper investigates the metal pad roll instability in liquid metal batteries, developing a numerical model to understand its mechanism and potential impact on large-scale energy storage systems.

Contribution

It introduces a combined fluid-electrodynamics numerical model to simulate and analyze the metal pad roll instability in cylindrical liquid metal batteries.

Findings

Identified the instability mechanism similar to aluminium reduction cells.

Provided initial results on growth rates and oscillation periods.

Highlighted the potential risk of short-circuiting in large LMBs.

Abstract

The increasing deployment of renewable energies requires three fundamental changes to the electric grid: more transmission lines, a flexibilisation of the demand and grid scale energy storage. Liquid metal batteries (LMBs) are considered these days as a promising means of stationary energy storage. Built as a stable density stratification of two liquid metals separated by a liquid salt, LMBs have three main advantages: a low price, a long life-time and extremely high current densities. In order to be cheap, LMBs have to be built large. However, battery currents in the order of kilo-amperes may lead to magnetohydrodynamic (MHD) instabilities, which - in the worst case - may short-circuit the thin electrolyte layer. The metal pad roll instability, as known from aluminium reduction cells, is considered as one of the most dangerous phenomena for LMBs. We develop a numerical model, combining fluid- and electrodynamics with the volume-of-fluid method, to simulate this instability in cylindrical LMBs. We explain the instability mechanism similar to that in aluminium reduction cells and give some first results, including growth rates and oscillation periods of the instability.