Liquid Metal Batteries
Research Group Liquid Metal Batteries
Source: Dr. Nimtz, Michael
With the growing role of solar and wind power in the German energy landscape, large scale storage becomes a key enabler for a functional power grid. In this setting, cost per unit stored energy and high number of charge and discharge cycles (low capacity fading) are the main criteria for a successful technology.
Liquid metal batteries, i.e. batteries in which both electrodes as well as the electrolyte are in the liquid state, are a very promising concept for economic storage. If abundant and cheap active materials can be used in large cells, the predicted total costs per unit stored energy are low and quite competitive.
A battery with fully liquid active interior has a number of advantages: when densities are chosen properly, the battery is self-assembling due to stable stratification. Liquid-liquid interfaces possess fast kinetics, thereby allowing for rapid charging and discharging, i.e., high rate capacity. Structureless (liquid) electrodes are insusceptible to aging providing nearly unlimited cyclability.
High current densities together with the large electrode areas of big cells imply a large total cell current and here electromagnetics together with fluid mechanics – i.e. magnetohydrodynamics – comes into play. In very large cells, the Lorentz force produced by the interaction of the cell current with it's own magnetic field may excite the Tayler instability (TI) that was demonstrated in our group by Seilmayer et al. (2012). Even in smaller cells, electromagnetic forces can drive so-called electro-vortex flows and excite interfacial waves. These waves typically arise at both interfaces of the three-layer system. Their interaction is determined by the ratio of the density jumps at the interfaces and, like the two cases mentioned above, can lead to a short circuit under extreme conditions. For safe operation of the batteries, such a situation must of course be ruled out. On the flip side, mild flows, particularly in the cathode and in the electrolyte, are beneficial to improve mass transport and thus to increase the efficiency of the cells.
We study flow phenomena and instabilities experimentally and numerically in connection with electrochemical processes in order to optimize the operating characteristics of LMBs.
At our battery laboratory we are able to perform electrochemical testing of electrodes, molten salt electrolytes and operation of small scale cells. For scale-up and efficiency improvement, testing of different container and isolator materials is essential to enable long term operation of cells.
2017, the first international workshop on liquid metal battery fluid dynamics (LMBFD 2017) was organized by our group and took place on May 16th and 17th 2017 in Dresden. The focus was on fluid dynamics and other aspects of liquid metal batteries and related devices (e.g., aluminum reduction cells). A second workshop on the fluid dynamics of liquid metal batteries was organized in November 2022 together with the Isaac Newton Institute (INI) in Cambridge frame of SOLSTICE. The talks are vailable on Youtube.
Research Topics and Exeriments
Battery Laboratory
For experiments, small cells are build and tested under argon atmosphere in the glove box.