Donald Sadoway has been a faculty member at MIT since 1978, where he has taught a solid-state chemistry course for 16 years. In addition to his teaching duties, he has also been directly involved in research into making batteries less expensive than lithium-ion batteries. Recently, MIT announced that Sadoway and his research partners have created an aluminum sulfur battery that could do just that. The research was conducted by scientists from Peking University, Yunnan University and Wuhan University of Technology in China; the University of Louisville in Kentucky; the University of Waterloo in Canada; Oak Ridge National Laboratory in Tennessee; and MIT.
The new battery architecture uses aluminum and sulfur as two electrode materials, with a molten salt electrolyte in between. As the price of lithium skyrockets due to growing demand, the world needs inexpensive alternatives. Aluminum and sulfur are plentiful and cheap. Sadoway says aluminum-sulfur battery cells will cost around $9 per kWh, which is far less than currently available lithium-ion battery cells. The new cells are not suitable for use in electric vehicles, but could reduce the cost of small-scale storage batteries for individuals and small businesses, which could make more lithium cells available for the transport sector. The research was published recently in the journal Nature.
Sadoway began by studying the periodic table, looking for cheap and abundant metals that could replace lithium. Iron, which is becoming an increasingly popular choice, doesn’t have the right electrochemical properties for an efficient battery, he says. But aluminum – the most abundant metal on Earth – does. “So, I said, well, let’s just make this a bookend. It will be aluminum,” he says.
Then we had to decide what to combine the aluminum with for the other electrode, and what type of electrolyte to put in between to transport the ions back and forth during charging and discharging. The cheapest of all nonmetals is sulfur, which therefore became the second electrode material. As for the electrolyte, “we weren’t going to use the volatile, flammable organic liquids” that have sometimes caused dangerous fires in cars and other lithium-ion battery applications, Sadoway says.
The researchers tried some polymers, but ended up looking at a variety of molten salts that have relatively low melting points — close to the boiling point of water instead of near 1,000°F for many salts. “Once you get down to near body temperature, it becomes practical” to make batteries that don’t require special insulation and anti-corrosion measures, he says.
The three ingredients they ended up with are cheap and readily available – aluminum, no different from aluminum foil at the supermarket; sulfur, which is often a waste product from processes such as petroleum refining; and widely available salts. “The ingredients are cheap and the thing is sure – it can’t burn,” Sadoway said. MIT News.
In their experiments, the team showed that the battery cells could sustain hundreds of cycles at exceptionally high charge rates. The rate of charge was closely related to the temperature of the electrolyte. At 110°C (230°F), the experimental batteries charged 25 times faster than at 25°C (77°F).
Serendipity is coming
The researchers chose the electrolyte simply because of its low melting point, but it turned out to have a significant advantage. One of the biggest issues with battery reliability is the formation of dendrites – narrow spikes of metal that collect on one electrode and eventually grow to come into contact with the other electrode. When this happens, it causes a short circuit, which not only hinders efficiency, but can also lead to “thermal runaway” – a polite way of saying a battery fire. But the electrolyte they started with proved to be very effective in preventing the formation of dendrites.
The chloro-aluminate salt they chose “essentially removed these runaway dendrites, while allowing for very fast charging,” says Sadoway. “We experimented at very high charging rates, charging in less than a minute, and we never lost any cells due to dendrite shorting.”
“It’s funny,” he says, because the focus was on finding a salt with the lowest melting point, but the catenated chloroaluminates they ended up with proved resistant. short circuit problem. “If we had started by trying to prevent dendritic shorting, I’m not sure I would have known how to pursue that,” Sadoway says. “I guess it was a fluke for us.”
The aluminum-sulfur battery does not need an external heat source
The researchers found that the aluminum-sulfur battery they were working on required no external heat source to maintain its operating temperature. Heat is naturally produced electrochemically by charging and discharging the battery. “As you charge, you generate heat, which prevents the salt from freezing. And then, when you unload, it also generates heat,” says Sadoway.
In a typical setup used for load leveling in a solar generation facility, for example, “you store electricity when the sun is shining, then you draw electricity after dark, and you every day. And that charge-idle-discharge-idle is enough to generate enough heat to keep the thing warm.
The smaller size of aluminium-sulfur batteries would also make them practical for uses such as electric vehicle charging stations. Sadoway says that when multiple electric cars want to charge at the same time, “if you want fast charging, the amperages are so high that we don’t have that amount of amperage in the line that feeds the facility.” Having an aluminum sulfur battery to store power and quickly release it when needed could eliminate the need to run expensive new power lines to service these chargers. Adding batteries to charging stations is already starting to happen in many places. The new batteries would significantly reduce the cost of adding battery storage to electric vehicle charging locations.
The new technology is already the basis of a spin-off company called Avanti, co-founded by Sadoway and Luis Ortiz, which licensed the patents for the system. “The first order of business for the company is to demonstrate that it works at scale,” Sadoway says, and then put it through a series of stress tests, including going through hundreds of charge cycles.
Would a sulfur-based battery cause the foul odors associated with some forms of sulfur? Not a chance, said Sadoway. “The rotten egg smell is in the gas, the hydrogen sulfide. It’s elemental sulfur, and it’s going to be locked inside the cells. If you were to try to crack open a lithium-ion cell in your kitchen, he says, “the moisture in the air would react and you would also start generating all kinds of noxious gases. These are legit questions, but the battery is sealed, it’s not an open container. So I wouldn’t worry about that.
New battery technologies are popping up all over the world, but anything named after Donald Sadoway is worth considering. Hands are wrung about the invasiveness of mining and the environmental consequences of finding battery materials. (Strangely, tearing up mountain tops and throwing them into the valleys below to reach the coal never seems to raise the same kind of concerns.) Creating new battery technologies that use some of the most abundant minerals on Earth seems like a evidence. , if the resulting performance is close to being acceptable for commercial uses.
This research also illustrates how the demonization of people who happen to be Chinese could delay essential research needed to effectively combat global warming. We’re all in this together, and it’s going to take all of us working together to keep the Earth habitable for future generations of humans. The need is great and the time has come. Let’s stop bickering and solve the problems we all face. It means electing representatives who will support clean energy for all of humanity.
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