Newswise — ALBUQUERQUE (N.M.) — Researchers from Sandia National Laboratories developed a new class molten sodium batteries that can be used for grid-scale energy storage. The new battery design was published in Cell Reports Physical Science today. Commercially available molten sodium battery, also known as sodium-sulfur, operate at temperatures between 520 and 660 degrees Fahrenheit. Sandia’s new Molten sodium-iodide Battery operates at a much cooler temperature of 230 degrees Fahrenheit. Leo Small, the project’s lead researcher, said that they have been trying to lower the operating temperature for molten sodium batteries as much as possible. Lowering the temperature of the battery can lead to a series of cost savings. You can use less expensive materials. You can use less expensive materials. The insulation required for batteries is lower and the wiring connecting them can be thinner. He said that a battery chemistry that works at temperatures of 550 degrees won’t work at 230 degrees. He cites the invention of a catholyte as one of the key innovations that allowed for lower operating temperatures. A catholyte, which is a liquid mixture consisting of two salts, is the result of the development of what he calls a catholyte. This basic lead-acid battery is commonly used for car ignition. It has a lead plate and lead dioxide plates with a sulfuric acids electrolyte in its middle. The lead plate reacts with sulfuric acids to form lead sulfate, and electrons, as energy is released from the battery. These electrons turn on the car and return to the opposite side of the battery. The lead dioxide plate uses the electrons as well as sulfuric acid to make lead sulfate. The new molten salt battery uses a liquid sodium metal as the lead plate. A small amount of gallium chloride is added to the liquid mixture. Erik Spoerke, a materials scientist, explained that the sodium metal creates electrons and sodium ions when energy is discharged from it. The electrons convert iodine to iodide and vice versa. The sodium ions travel across a separator to reach the other side, where they react with the Iodide ions to create molten sodium-iodide salt. The middle of the battery has a special ceramic separator, which allows only sodium ions to move side to side. Spoerke stated that unlike a lithium-ion battery, our system is liquid on both sides. This means that we don’t have the need to deal with issues such as the material falling apart or changing its phase. It’s all liquid. These liquid-based batteries have a longer life span than other batteries. These liquid-based batteries don’t have as long a life span as other batteries. Martha Gross, a postdoctoral researcher, has been working on laboratory tests for the past 2 years. She performed experiments charging and discharging a battery 400 times over the eight months. Then, the experiment was halted for a month to let the molten salt and catholyte cool to room temperature, and then freeze. Gross was happy to see that the battery worked even after being heated up. This means that the sodium-iodide cells could still be used in the event of a large-scale disruption in energy supply, such as the one in Texas in February. Spoerke explained that sodium-iodide batteries are safer and can be warmed up, charged, and then returned to normal operation after the disruption has passed. Spoerke stated, “A lithium-ion battery can catch on fire if there is a failure within the battery. This leads to runaway overheating. Our battery chemistry has proven that this cannot happen. If you take out the ceramic separator and allow the sodium metal to mix in with the salts, the battery will not fail. The battery will stop working, but there is no chemical reaction or fire. Small explained that a sodium-iodide-based battery can be destroyed by an external fire. However, it should not cause any further damage to the fire. This voltage results in a higher energy density. Future batteries made with this chemistry will require fewer cells, fewer connections between them, and a lower unit cost to store the same amount. Gross said, “We were really excited by how much energy we could possibly cram into this system because of the new catholyte that we’re reporting here.” “Molten sodium battery have been around for decades and are all over the world, but nobody ever talks about them. It’s quite impressive to be able to lower the temperature, and then come back with numbers and say that this is a viable system. Small stated that the next step in the sodium-iodide project is to refine and tune the catholyte chemical to replace the gallium-chloride component. Spoerke said that gallium chloride is extremely expensive, more than 100x more expensive than table salt. The team is also working on engineering tweaks to make the battery charge and discharge more quickly. One modification that was previously identified to speed up battery charging was to cover the molten sodium side with a thin layer tin. The remaining challenges are commercialization challenges and not technical ones. Spoerke stated that this is the first demonstration of stable, long-term cycling of a low temperature molten-sodium battery. “The magic of what you’ve created is that we have identified salt chemistry as well as electrochemistry that allows us to operate at 230 degrees Fahrenheit. This low-temperature sodium iodide configuration is a new definition of what it means for a molten salt battery. The Department of Energy’s Office of Electricity Energy Storage Program Sandia National Laboratories supported the development of the new sodium batteries. National Technology and Engineering Solutions of Sandia LLC is a multimission laboratory that is owned by Honeywell International Inc. for the U.S. Department of Energy. Sandia Labs is responsible for major research and development in nuclear deterrence and global security. Its main facilities are located in Albuquerque (New Mexico) and Livermore (California).