- Titel
- Modeling electrochemical processes in liquid metal batteries with a focus on mass transfer in molten salt electrolytes
- Zitierfähige Url:
- https://nbn-resolving.org/urn:nbn:de:bsz:14-qucosa2-1000615
- Übersetzter Titel (DE)
- Modellierung von elektrochemischen Vorgängen in Flüssigmetallbatterien mit Fokus auf Stofftransport in Salzschmelz-Elektrolyten
- Erstveröffentlichung
- 2025
- Datum der Einreichung
- 20.02.2025
- Datum der Verteidigung
- 16.09.2025
- Abstract (EN)
- Electrical energy storage devices are necessary to meet the world’s increasing energy demand, while transitioning to intermittently available renewable energies. Liquid metal batteries are a promising technology in that field. They can be classified into two different cell types and multiple material pairings for their electrodes are possible. First, there are concentration cells, where batteries based on lithium and bismuth are a maturely developed representative. Second, there are displacement cells, which are currently developed with sodium and zinc as electrode materials. Despite having different working principles, they both consist of molten metal electrodes with a molten salt electrolyte in between, stably layered and self-segregating due to their density differences. Na-Zn displacement cells can employ a porous separator within the electrolyte layer. Furthermore, they are a favorable storage option due to their high theoretical cell potential, readily abundant materials and cost-advantages. Hence, investigations are here targeted at this type of liquid metal battery. Multi-physical and multi-dimensional considerations are necessary to investigate liquid metal batteries, making this a highly complex matter and numerical modeling as well as experimental research are nontrivial. Even though, concentration cells have widely been investigated in recent years, the findings from these studies are not entirely transferable to Na-Zn cells. Moreover, they face the problem of mass transfer-induced self-discharge, which makes it necessary to understand fluid dynamics in the whole cell, and especially in the electrolyte. A diaphragm has often been proposed to reduce self-discharge – which is caused by transport of electroactive species – without demonstrating its efficacy and exact influence. Unfortunately, this conflicts with concentration gradients that largely influence cell efficiency, which are only reduced if the respective cell areas are set into motion. Focusing on the liquid metal batteries’ electrolyte, species transport in the stagnant electrolytes of Li-Bi cells is investigated first. At the same time, a cell voltage model for Li-Bi liquid metal batteries is developed. This is followed by an assessment on flow phenomena likely to occur in Na-Zn batteries, where solutal convection, swirling flow, electrocapillary Marangoni convection and droplet formation are shown to be of most significance. Detailed investigations on solutal convection are conducted. In so doing, the diaphragm’s influence on solutal based self-discharge is studied. Using the finite-volume method within the OpenFOAM framework, a numerical solver is established. Besides including the cell voltage model, which considers interface reactions in the electrochemical double layer, the solver is able to account for species transfer due to migration, diffusion and advection in the electrolyte as well as in the cathode. Furthermore, it is possible ito address the influence of porous media. Besides having revealed that mass transport and concentration gradients have a significant effect on cell performance, it is confirmed that there must be flow in the electrolyte. In terms of solutal convection, resulting from unstable density gradients, a charge-discharge asymmetry during cycling is identified: convective flow is always present in one electrolyte compartment while the other compartment is stably stratified. However, phenomena during cell cycling depend largely on the previous cycles. Despite experiencing flow, minor areas of the electrolyte are still stably layered and cannot be disrupted by the gentle solutal flow. Furthermore, the importance of a flow barrier to reduce self-discharge is demonstrated. Nevertheless, such a barrier is not able to fully mitigate self-discharge, as species transport via migration and diffusion are still possible. Consequently, an optimization of operational current density, charging time and diaphragm properties are necessary to limit self-discharge and improve the performance of Na-Zn liquid metal batteries.
- Freie Schlagwörter (EN)
- Liquid Metal Batteries, Molten Salt Electrolytes, Solutal Convection, OpenFOAM
- Klassifikation (DDC)
- 620
- Klassifikation (RVK)
- ZP 4130
- GutachterIn
- Prof. Dr. Kerstin Eckert
- Prof. PhD Douglas H. Kelley
- Prof. PhD Kristian Etienne Einarsrud
- BetreuerIn Hochschule / Universität
- Prof. Dr. Kerstin Eckert
- Dr. Norbert Weber
- BetreuerIn - externe Einrichtung
- Dr. Tom Weier
- Den akademischen Grad verleihende / prüfende Institution
- Technische Universität Dresden, Dresden
- Förder- / Projektangaben
- European Union Horizon2020
Sodium-Zinc molten salt batteries for low-cost stationary storage
(SOLSTICE) - Sonstige beteiligte Institution
- Helmholtz-Zentrum Dresden-Rossendorf e.V., Dresden
- Version / Begutachtungsstatus
- publizierte Version / Verlagsversion
- URN Qucosa
- urn:nbn:de:bsz:14-qucosa2-1000615
- Veröffentlichungsdatum Qucosa
- 30.10.2025
- Dokumenttyp
- Dissertation
- Sprache des Dokumentes
- Englisch
- Lizenz / Rechtehinweis
CC BY-NC 4.0