Molten salt batteries shape as a more cost-effective solution, which use electrodes kept in a molten state with the help of high temperatures. This is something that the Sandia scientists have been working to change. //

"We've been working to bring the operating temperature of molten sodium batteries down as low as physically possible," says Leo Small, the lead researcher on the project. "There's a whole cascading cost savings that comes along with lowering the battery temperature. You can use less expensive materials. The batteries need less insulation and the wiring that connects all the batteries can be a lot thinner."

In their commercial form, these batteries are known as sodium-sulfur batteries, and a few of these have been developed around the world but generally operate at 520 to 660 °F (270 to 350 °C). The Sandia team have set their sights much lower, although doing so required a rethink as the chemistries that work at high temperatures don't lend themselves well to lower temperatures.

The scientists' design consists of liquid sodium metal that sits on the opposite side of a ceramic separator material to a novel liquid mixture made of sodium iodide and gallium chloride, which the scientists call a catholyte. When the battery discharges energy, chemical reactions take place that produces sodium ions and electrons that pass through the highly-selective separator material and produce molten iodide salt on the other side. //

This sodium-sulfur battery proved capable of operating at just 230 °F (110 °C), and proved its worth across eight months of testing in the lab through which it was charged and discharged more than 400 times. Further, it runs at 3.6 volts, which the scientists say is around 40 percent higher than commercially available molten salt batteries. This could equate to versions with fewer cells and therefore a higher energy density.