Sandia National Laboratories Looks to Reinvent the Molten Sodium Battery for Grid Scale Energy Storage

August 13, 2021 by Ahmad Ezzeddine

Researchers at Sandia National Laboratories have designed an all-liquid sodium battery that could operate at a lower temperature than its predecessors.

A new molten sodium-iodide battery might be a better replacement for the sodium-sulfur batteries currently used on a commercial scale. The research from Sandia National Laboratories shows that Sodium-Iodide batteries could operate at 230°F. This temperature is so much lower than the operating temperature in commercial Sodium-Sulfur batteries at around  520-660°F.

Postdoctoral researcher Martha Gross works in an argon glove box with a test battery cell illustrating a lab-scale sodium iodide battery. Image courtesy of Sandia National Laboratories

The Cell Design

The cell is designed of a molten sodium anode. The cathode consists of a mixture of sodium iodide and gallium chloride. To separate the anode from the cathode the researchers used two polymeric O-rings and an electrolyte separator called NaSICON.

“In our system, unlike a lithium-ion battery, everything is liquid on the two sides,” said Erik Spoerke, a materials scientist who has been working on molten sodium batteries for more than a decade. “That means we don’t have to deal with issues like the material undergoing complex phase changes or falling apart; it’s all liquid. Basically, these liquid-based batteries don’t have as limited a lifetime as many other batteries.”

Sandia National Laboratories researchers Leo Small, back right, and Erik Spoerke, back left, observe as Martha Gross, front, works in an argon glove box on their lab-scale sodium iodide battery. Image courtesy of Sandia National Laboratories.

Battery Usage in Large Scale Energy Storage

In the case of large-scale energy disruptions, Sodium-Iodide batteries could be used. After using the batteries, they are cooled down. After the disruption ends, the batteries are warmed again and recharged without having a costly operation. The battery’s chemistry is special since through this operation the battery doesn’t have an internal chemical degradation.


Reduced Temperature 

Having the battery operate at 110 °C, major financial and technical problems are overcome. The less the operating temperature means less wiring thickness, and less heat insulation materials used. Moreover, in case of an error in the battery, the battery doesn’t burn as other batteries do. Even if the battery catches fire from the surroundings, it might fail or crack, but it won’t act as fuel to the fire.


Operating Voltage

The researchers were able to operate the battery at 3.65 volts, the commercial Sodium-Sulfur cells usually operate at 2.1 to 2.2 volts. With this increase in the operating voltage, the number of cells used is less therefore the number of cell connections is less, therefore a lower cost per charge capacity is assured.

“We were really excited about how much energy we could potentially cram into the system because of the new catholyte we’re reporting in this paper,” Gross said. “Molten sodium batteries have existed for decades, and they’re all over the globe, but no one ever talks about them. So, being able to lower the temperature and come back with some numbers and say, ‘this is a really, really viable system’ is pretty neat.”


Potential Future Research

The researchers are not yet done with developing the battery. Gallium Chloride is known as an expensive substance. Therefore, the researchers are looking for a replacement material or salt to use instead of Gallium Chloride.

The researchers are also cutting through some non-technical challenges which are the only remaining challenges to get the battery to market. 

 Enhancing the charging time and the charging capacity of the battery is another work the researchers are trying to accomplish.

This research was supported by the Department of Energy’s Office of Electricity Energy Storage Program.