Large Amounts of Energy Storage
Researchers have created a new type of battery that is entirely made of abundant and inexpensive elements. If this battery is successful, it could provide low-cost backup storage for renewable energy sources such as wind and solar.
It is possible that an aluminum-sulfur battery made from inexpensive and easily obtained ingredients could provide backup storage for renewable energy sources at a reasonable cost.
As more extensive wind and solar power installations are built around the world, there is a growing demand for reasonably priced, large-scale backup power systems that can supply electricity even when the wind and sun are not blowing. Because of their high cost, today’s lithium-ion batteries are unsuitable for the vast majority of such applications. Other options, such as pumped hydro, necessitate highly specific topography, which is not always readily available.
Scientists at MIT and other institutions have developed a new type of battery that may help to bridge that gap. This battery is made entirely of readily available and low-cost components.
The new battery architecture, which uses aluminum and sulfur as electrode materials and a molten salt electrolyte in between, was published today in the journal Nature (August 24, 2022). The study was co-authored by Donald Sadoway, an MIT professor, and fifteen other researchers from MIT and other institutions in China, Canada, Kentucky, and Tennessee.
“I wanted to invent something better, much better, than lithium-ion batteries for small-scale stationary storage, and eventually for automotive [uses,” explains Sadoway, the John F. Elliott Professor Emeritus of Materials Chemistry. “I wanted to create something that was far superior to lithium-ion batteries for small-scale stationary storage.”
Because lithium-ion batteries contain an ignitable electrolyte and are expensive, transporting them is not the best way to use them. As a result, Sadoway began searching the periodic table for any inexpensive and naturally abundant metals that could serve as a suitable substitute for lithium. He claims that iron, the metal that dominates the commercial market, lacks the necessary electrochemical properties for an effective battery. Despite the fact that aluminum is the most abundant metal on Earth and the second most abundant metal in the market, copper is the most abundant metal in the market. “As a result, I proposed that we turn that into a bookend,” she explained. He believes the material will be aluminum.
Battery with Aluminum Sulfur
The next step was to decide what would be used as the second electrode alongside the aluminum, as well as the type of electrolyte that would be placed in the middle to facilitate ion movement during the charging and discharging processes. Sulfur was chosen as the second electrode material because it is the least expensive of all nonmetals. “We were not going to use the volatile, flammable organic liquids,” Sadoway says of the electrolyte.
These organic liquids are sometimes the source of dangerous fires in automobiles and other lithium-ion battery applications. They experimented with various polymers, but ultimately focused on molten salts with relatively low melting temperatures — close to the boiling point of water, as opposed to the melting point of typical salts, which is nearly 1,000 degrees Fahrenheit (538 degrees Celsius). “Once you get down to near body temperature,” he says, “it becomes practical” to design batteries that don’t require special insulation or anticorrosion techniques. Making such batteries becomes “practically impossible once you get down to near body temperature.”
In the end, they were able to get by with three inexpensive and easily accessible ingredients. The first is aluminum, which is the same as aluminum foil from the grocery store. The second element is sulfur, which is frequently produced as a byproduct of operations such as petroleum refining. Last but not least, easily accessible salts. “The materials are inexpensive, and the product is risk-free because it cannot catch fire,” says Sadoway.
Testing by the team revealed that the battery cells could withstand hundreds of cycles at extremely fast charging rates. Furthermore, the scientists estimated that the cost per cell would be about one-sixth of that of equivalent lithium-ion cells. They discovered that the working temperature had a significant impact on the charging rate, with rates 25 times faster at 110 degrees Celsius (230 degrees Fahrenheit) than at 25 degrees Celsius (77 degrees Fahrenheit).
Molten salt was the team’s electrolyte of choice due to its low melting point, which turned out to be an unexpected decision because it had a fortunate benefit. Dendrites are thin metal spikes that form on one electrode of a battery and eventually grow across to contact the other electrode, causing a short circuit and lowering the overall efficiency of the battery. Dendrite formation is one of the most significant issues affecting battery dependability. This particular salt happens to be particularly effective at avoiding the aforementioned issue.
Sadoway claims that the chloro-aluminate salt used “basically retired these runaway dendrites while also allowing for very quick charging.” We ran our experiments at extremely fast charging rates, finishing in under a minute, and we saw no cell loss as a result of dendritic shorting.
“It’s funny,” he says, “because the whole goal was to find a salt with the lowest melting point,” but the catenated chloro-aluminates they ended up with were resistant to shorting. “It’s funny,” he says, “because the whole thing revolved around finding the salt with the lowest melting point.” “I’m not sure I would have known how to pursue that if we had started by attempting to prevent dendritic shorting,” Sadoway adds. “I’m not sure how I would have pursued that.” I suppose it was a stroke of luck for us.
Furthermore, the battery does not require an additional source of heat to maintain a stable operating temperature. The heat is produced naturally and unavoidably by the electrochemical process of charging and discharging the battery. “When you charge, heat is produced, which keeps the salt from freezing. “When you discharge, you generate heat,” Sadoway says. “When you discharge it, it generates electricity.”
In a typical load-leveling arrangement at a solar production facility, “you would store electricity when the sun is shining, and then you would draw electricity after dark, and you would do this every day.” And that cycle of charging, idling, discharging, and idling generates enough heat to keep the object at a constant temperature.
According to him, this new battery composition would be ideal for installations of the size required to power a single home or a small to medium business, with storage capacity of a few tens of kilowatt-hours.
Other technologies, such as the liquid metal batteries developed by Sadoway and his students several years ago and used as the foundation for a spinoff company called Ambri, which hopes to deliver its first products within the next year, may be more effective for larger installations, ranging from tens to hundreds of megawatt hours. Sadoway and his students developed a battery as an example of such technology. Sadoway was recently awarded this year’s European Inventor Award for creating that product.
According to Sadoway, the smaller size of the aluminum-sulfur batteries would allow them to be used in applications such as electric vehicle charging stations. “If you try to do that with batteries and you want rapid charging, the amperages are just so high that we don’t have that amount of amperage in the line that feeds the facility,” he says, referring to when electric vehicles become common enough on the roads that several cars want to charge up at the same time, as happens today with gasoline fuel pumps.
He makes the point that when electric vehicles become common enough on the road that multiple cars want to charge at the same time, “If you try it with batteries, As a result, if a battery system like this one is used to store power and then make it readily available when needed, it may not be necessary to install costly new power lines to serve these chargers.
Avanti is a new spinoff firm co-founded by Sadoway and Luis Ortiz ’96 ScD ’00, who was also a co-founder of Ambri. It has leased the patents to the system and is based on the new technology. According to Sadoway, “the first order of business for the company is to demonstrate that it works at scale,” and then they will put it through a series of stress tests, including hundreds of charging cycles.
Is there a chance that a battery made of sulfur would emit the pungent scents that are typically associated with certain types of sulfur? According to Sadoway, not a chance. The odor of rotting eggs is caused by the gas hydrogen sulfide. This is sulfur in its elemental form, which will be encapsulated within the cells. As he explains (and please don’t try this at home! ), if you tried to open a lithium-ion cell in your kitchen, “the moisture in the air would react, and you’d start generating all sorts of unpleasant fumes as well.” These are valid concerns, but the battery is not an open container; it is hermetically sealed. As a result, you should not be concerned about it.
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