Molten Sodium Batteries Improve Grid-Scale Energy Storage

Researchers at Sandia National Laboratories have designed a new class of molten sodium batteries for grid-scale energy storage.

The development of the new sodium battery was supported by the Department of Energy’s Office of Electricity Energy Storage Program.

The findings have been published in the scientific journal Cell Reports Physical Science.

The researchers stated that Sandia’s new molten sodium-iodide battery operates at a much lower 230 degrees Fahrenheit than the commercially available molten sodium batteries, which typically operate at 520-660 degrees Fahrenheit.

“We’ve been working to bring the operating temperature of molten sodium batteries down as low as physically possible,” said Leo Small, the lead researcher on the project. “There’s a whole cascading cost saving 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,” Small added.

According to the researchers, the major innovation that allowed the new molten sodium-iodide battery to operate at a lower temperature was the development of a catholyte. A catholyte is a liquid mixture of two salts: sodium iodide and gallium chloride.

Sandia’s small, lab-scale sodium-iodide battery was rigorously tested for eight months inside an oven. It was charged and discharged more than 400 times.

Due to the Covid-19 pandemic, researchers had to pause the experiment for a month and let the molten sodium and the catholyte cool down to room temperature and freeze. The battery warmed up without much hassle to the researcher’s relief.

According to Erik Spoerke, a materials scientist, sodium-iodide batteries could be used if a large-scale energy disruption were to occur. The sodium-iodide batteries could be allowed to cool until frozen. Once the disruption is over, they could be warmed up, recharged, and returned to regular operation without a lengthy or costly start-up process and without degradation of the battery’s internal chemistry.

Commenting on the safety of sodium-iodide batteries, Spoerke said, “A lithium-ion battery catches on fire when there is a failure inside the battery. We’ve proven that cannot happen with our battery chemistry. Furthermore, at 3.6 volts, the new sodium-iodide battery has a 40% higher operating voltage than a commercial molten sodium battery. This voltage leads to higher energy density. As a result, potential future batteries made with this technology would need fewer cells, fewer connections between cells, and an overall lower unit cost to store the same amount of electricity, Small said.

Commercial molten sodium batteries have a lifespan of 10-15 years, significantly longer than standard lead-acid batteries or lithium-ion batteries.

According to Small, the next step for the sodium-iodide battery project is to refine the catholyte chemistry to replace the gallium chloride component, which is 100 times as expensive as table salt.

The experts are also working on getting the battery to charge and discharge faster.

Spoerke added that it would likely take five to ten years for sodium-iodide batteries to be commercially available.

As the demand for different sustainable energy sources continues to rise worldwide, efforts are underway globally to develop different kinds of batteries for energy storage.

Last year, U.K.-based Faradion Ltd, a manufacturer of sodium-ion batteries, had announced a partnership with Infraprime Logistics Technologies to provide batteries for commercial vehicles in the Indian electric vehicle market.

Earlier, researchers at the Washington State University and Pacific Northwest National Laboratory had created a sodium-ion battery that could be made with widely and cheaply available materials.