The team at the Department of Materials Science and Engineering at the Norwegian University of Science and Technology ( NTNU) in Trondheim have developed a battery system with three liquid layers: sodium at the top as the negative electrode, a sodium chloride based electrolyte in the middle, and zinc at the bottom as the positive electrode.
To prevent the zinc containing ions from reacting with the sodium electrode, a porous diaphragm or separator is placed between the electrodes. Avoiding a brittle, expensive β-alumina ion selective membrane and replacing it with a cheap durable diaphragm material significantly improves the performance and reduces the cost of liquid metal batteries.
The choice of immiscible electrolytes and electrodes will ensure a safe battery system, which in the unlikely event of mechanical failure will discharge without any undesired effects such as fire or explosion. This compares to sodium sulphur (NaS) molten salt batteries which have been demonstrated for grid storage. They require a sodium ion selective membrane which adds a great deal of expense and resistance to the cell and in the event of rupture or cracking of the membrane a vigorous reaction occurs, possibly resulting in fires.
The team at NTNU are working with local molten salt electrochemistry expert SINTEF on lab scale cell design and development as well as the testing of the battery performance and materials.
The project is funded by The Research Council of Norway and runs until 2018.