Researchers at Sandia National Laboratories have designed a brand new class of molten sodium batteries for grid-scale vitality storage. The new battery design was shared in a paper printed in the present day within the scientific journal Cell Reports Physical Science.
Molten sodium batteries have been used for a few years to retailer vitality from renewable sources, corresponding to photo voltaic panels and wind generators. However, commercially obtainable molten sodium batteries, known as sodium-sulfur batteries, sometimes function at 520-660 levels Fahrenheit. Sandia’s new molten sodium-iodide battery operates at a a lot cooler 230 levels Fahrenheit as a substitute.
“We’ve been working to convey the working temperature of molten sodium batteries down as little as bodily attainable,” stated Leo Small, the lead researcher on the venture. “There’s an entire cascading value financial savings that comes together with decreasing the battery temperature. You can use cheaper supplies. The batteries want much less insulation and the wiring that connects all of the batteries is usually a lot thinner.”
However, the battery chemistry that works at 550 levels does not work at 230 levels, he added. Among the key improvements that allowed this decrease working temperature was the event of what he calls a catholyte. A catholyte is a liquid combination of two salts, on this case, sodium iodide and gallium chloride.
Basics of constructing higher batteries
A fundamental lead-acid battery, generally used as a automotive ignition battery, has a lead plate and a lead dioxide plate with a sulfuric acid electrolyte within the center. As vitality is discharged from the battery, the lead plate reacts with sulfuric acid to kind lead sulfate and electrons. These electrons begin the automotive and return to the opposite facet of the battery, the place the lead dioxide plate makes use of the electrons and sulfuric acid to kind lead sulfate and water. For the brand new molten sodium battery, the lead plate is changed by liquid sodium steel, and the lead dioxide plate is changed by a liquid combination of sodium iodide and a small quantity of gallium chloride, stated Erik Spoerke, a supplies scientist who has been engaged on molten sodium batteries for greater than a decade.
When vitality is discharged from the brand new battery, the sodium steel produces sodium ions and electrons. On the opposite facet, the electrons flip iodine into iodide ions. The sodium ions transfer throughout a separator to the opposite facet the place they react with the iodide ions to kind molten sodium iodide salt. Instead of a sulfuric acid electrolyte, the center of the battery is a particular ceramic separator that permits solely sodium ions to maneuver back and forth, nothing else.
“In our system, not like a lithium ion battery, the whole lot is liquid on the 2 sides,” Spoerke stated. “That means we do not have to take care of points like the fabric present process advanced part modifications or falling aside; it is all liquid. Basically, these liquid-based batteries haven’t got as restricted a lifetime as many different batteries.”
In truth, industrial molten sodium batteries have lifetimes of 10-15 years, considerably longer than customary lead-acid batteries or lithium ion batteries.
Long-lasting batteries which are safer
Sandia’s small, lab-scale sodium-iodide battery was examined for eight months inside an oven. Martha Gross, a postdoctoral researcher who has labored on the laboratory assessments for the previous two years, performed experiments charging and discharging the battery greater than 400 occasions over these eight months.
Because of the COVID-19 pandemic, they needed to pause the experiment for a month and let the molten sodium and the catholyte cool all the way down to room temperature and freeze, she stated. Gross was happy that after warming the battery up, it nonetheless labored.
This signifies that if a large-scale vitality disruption had been to happen, like what occurred in Texas in February, the sodium-iodide batteries might be used, after which allowed to chill till frozen. Once the disruption was over, they might be warmed up, recharged and returned to regular operation and not using a prolonged or expensive start-up course of, and with out degradation of the battery’s inside chemistry, Spoerke added.
Sodium-iodide batteries are additionally safer. Spoerke stated, “A lithium ion battery catches on hearth when there’s a failure contained in the battery, resulting in runaway overheating of the battery. We’ve confirmed that can’t occur with our battery chemistry. Our battery, in case you had been to take the ceramic separator out, and permit the sodium steel to combine with the salts, nothing occurs. Certainly, the battery stops working, however there is not any violent chemical response or hearth.”
If an outdoor hearth engulfs a sodium-iodide battery, it’s possible the battery will crack and fail, however it should not add gas to the fireplace or trigger a sodium hearth, Small added.
Additionally, at 3.6 volts, the brand new sodium-iodide battery has a 40% greater working voltage than a industrial molten sodium battery. This voltage results in greater vitality density, and that signifies that potential future batteries made with this chemistry would want fewer cells, fewer connections between cells and an general decrease unit value to retailer the identical quantity of electrical energy, Small stated.
“We had been actually enthusiastic about how a lot vitality we might probably cram into the system due to the brand new catholyte we’re reporting on this paper,” Gross added. “Molten sodium batteries have existed for many years, and so they’re everywhere in the globe, however nobody ever talks about them. So, with the ability to decrease the temperature and are available again with some numbers and say, ‘it is a actually, actually viable system’ is fairly neat.”
The way forward for sodium-iodide batteries
The subsequent step for the sodium-iodide battery venture is to proceed to tune and refine the catholyte chemistry to exchange the gallium chloride element, Small stated. Gallium chloride may be very costly, greater than 100 occasions as costly as desk salt.
The staff can be engaged on varied engineering tweaks to get the battery to cost and discharge sooner and extra absolutely, Spoerke added. One beforehand recognized modification to hurry up the battery charging was to coat the molten sodium facet of the ceramic separator with a skinny layer of tin.
Spoerke added that it will possible take 5 to 10 years to get sodium-iodide batteries to market, with many of the remaining challenges being commercialization challenges, reasonably than technical challenges.
“This is the primary demonstration of long-term, secure biking of a low-temperature molten-sodium battery,” Spoerke stated. “The magic of what we have put collectively is that we have recognized salt chemistry and electrochemistry that permit us to function successfully at 230 levels Fahrenheit. This low-temperature sodium-iodide configuration is type of a reinvention of what it means to have a molten sodium battery.”
The growth of the brand new sodium battery was supported by the Department of Energy’s Office of Electricity Energy Storage Program.