Molten-salt batteries

Molten-salt batteries, including sodium-nickel-chloride and sodium-sulfur batteries, are based on abundant raw materials. The former consist of a sodium-metal anode and a nickel-chloride cathode separated by a ceramic sodium-b’’-alumina electrolyte and is commercialized by our industry partner FZSonick. Upon discharge, sodium is transported to the cathode compartment and reacts to form sodium-chloride (table salt) and nickel. Sodium-nickel-chloride batteries are a very safe battery technology with no risk of thermal runaway or toxic gas evolution. In addition, these batteries unlike lithium-ion batteries tolerate environmental temperatures of -40°C to 60°C. This property makes these batteries a prime choice for delivering backup power for outdoor mobile telecom antennas. Our research aims at improving the power capability of these batteries to maintain competitiveness with lithium-ion battery technology for electromobility (delivery vehicles, shuttle buses. larger public buses, etc.) and stationary storage application (grid stabilization, etc.). Sodium-nickel-chloride batteries are also integrated and studied at the Empa Energy Hub.
Fig. 1: a) Photograph of sodium nickel chloride cell with superimposed schematics. b) and c) Scanning electron microscopy images of sodium-beta’’-alumina electrolyte sintered at different conditions resulting in very different microstructure.


Our lab focuses on understanding the impact of microstructure and phase composition on the mechanical strength and on the ionic conductivity of the sodium-b’’-alumina electrolyte. These two properties are directly correlated with the power capability of the battery, but also with production cost, as thinner electrolytes results in improved power capability, but lower yield in production. Although known since the 1970s, processing of sodium-β’’-alumina into a dense material with high ion conductivity is challenging, in particular due to significant sodium loss during sintering. Reports in literature relating microstructure to ionic transport properties are lacking and reported values for the ionic conductivity vary significantly. We developed a detailed understanding, how microstructure and phase composition affect ionic conductivity and mechanical strength. Our results are also relevant for related ceramic electrolytes for all-solid-state lithium-ion batteries.


Swiss Federal Office of Energy, InnoSuisse, Horizon 2020

Selected publications


[1]  M. V. F.Heinz, L. Sieuw, T. Lan, A. Turconi, D. Basso, F. Vagliani, A. Pozzi, C. Battaglia, Cell design strategies for sodium-zinc chloride (Na-ZnCl2) batteries, and first demonstration of tubular cells with 38 Ah capacity, Electrochimica Acta, 2023, 142881.

[2] T. Lan, G. Graeber, L. Sieuw, E. Svaluto-Ferro, F. Vagliani, D. Basso, A. Turconi, C. Battaglia, M. V. F. Heinz, Planar sodium-nickel chloride batteries with high areal capacity for sustainable energy storage, Adv. Funct. Materials 2023, 230240.

[3] D. Landmann, E. Svaluto-Ferro, M.V.F. Heinz, P. Schmutz, C. Battaglia, Elucidating the rate-limiting processes in high-temperature sodium-metal chloride batteries Adv. Science 2022, 2201019.

[4]  D. Landmann, G. Graeber, M.V.F. Heinz, S. Haussener, C. Battaglia, Sodium plating and stripping from Na-β''-alumina ceramics beyond 100 mA/cm2, Materials Today Energy, 2020, 18, 100515.

[5] G. Graeber, D. Landmann, E. Svaluto-Ferro, F. Vagliani, A. Turconi, M.V.F. Heinz, C. Battaglia, Rational cathode design for high-power sodium-nickel chloride batteries, Adv. Funct. Materials 2021, 210667.

[6] M. V. F. Heinz, G. Graeber, L. Landmann, C. Battaglia, Pressure management and cell design in solid-elecrolyte batteries, at the example of sodium nickel-chloride batteries, J. Power Sources, 2020, 465, 228268.

[7] M.-C- Bay, M. Wang, R. Grissa, M. Heinz, J. Sakamoto, C. Battaglia, Sodium plating from Na-b''-alumina ceramics at room temperature, paving the way for fast-charging all-solid-state batteries, Adv. Energy Materials 2019, 1902899.

[8] M.-C. Bay, M. V. F. Heinz, R. Figi, C. Schreiner, D. Basso, N. Zanon, U. Vogt, C. Battaglia, ACS Appl. Energy Materials 2018, 2, 687.



Press releases
Falling Walls - Empa Scientists among the winners, Empa press release, 10.11.2020 (English)
Die Batterie neu erfinden, BFE Fachartikel published in Swiss Engineering, 15.8.2022 (Deutsch)