Study on Corrosion Control and Low-Temperature Electrolytes for Low-Cost Na-based Liquid Metal Batteries

• Applicants: Dr. Thomas Bauer; Professor Dr. Georg Müller
• Subject Area: Chemical and Thermal Process Engineering ; Energy Process Engineering
• Term: from 2019 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 411450529

Liquid metal battery (LMB) is an intriguing energy storage technology with advantages of low-cost, large-capacity and long-lifespan. Recently, it has been gained great interest as a large scale electricity storage device able to integrate the intermittent renewable energy technologies like wind and solar into the grid.In general, a liquid metal battery consists of a low-density liquid metal A as negative electrode (e.g Li, Na, Mg), a medium-density molten salt electrolyte (a mixture of molten salts like NaCl, MgCl2, LiCl, NaF, NaI) and a high-density liquid metal B as positive electrode (Sb, Pb, Bi, ….). A seal (i.e. a ceramic insulator) is applied to isolate the negative current collector (NCC) from the positive current collector (PCC). Due to the density difference and the mutual immiscibility, the liquid metal electrodes and the molten salt electrolyte will be self-segregated into three layers when heated to the working temperature range of 300-700°C (depending on the electrode/electrolyte material systems). The molten salt electrolyte also serves as an isolation layer between the negative and positive electrodes to replace the battery separator existing in traditional batteries. The strong interaction between the two liquid metals A and B provides the thermodynamic driving force (cell voltage) for the liquid metal cell. Despite that Li-based LMBs possess excellent electrochemical performance], the excessive consumption of Li resource (e.g. Li-ion batteries for transport sector) will inevitably lead to a rapidly increasing price, which makes low cost Na-based LMBs more competitive in large scale energy storage for the future energy system.The major challenges that could affect commercial deployment of LMB are the corrosion of positive current collector, the sealing material aging and the solubility of negative electrode material into electrolyte are. The research proposal general objective is to develop an efficient (discharge voltage > 0.5 V), long-life (>20 years) and low-cost (< 250$/kWh) liquid metal battery system. It will be based on new combinations of liquid metal electrodes (Na//SbSn and Na//BiSb) and on a Na-based salts electrolyte with melting point <450°C, and the solubility of Na in electrolyte <0.5 mol%. To achieve this objective, the above identified major challenges will be addressed both theoretically and experimentally as follows: (i) evaluation of the corrosion mechanism and the development of corrosion resistant materials for the components in contact with the positive electrode, (ii) evaluation and selection of the best sealing materials/coatings required for a safe operation of the LMB, (iii) selection of the molten salt electrolyte composition with the best thermo-chemical properties and the lowest Na solubility.

• DFG Programme: Research Grants
• International Connection: China
• Partner Organisation: National Natural Science Foundation of China
• Cooperation Partner: Professorin Dr. Kangli Wang