According to a new paper published in the journal Nature, MIT researchers describe new aluminum-sulfur batteries that are made entirely of abundant and inexpensive materials and can be charged in less than a minute. “A new battery architecture that uses aluminum and sulfur as the two electrode materials, with a molten salt electrolyte between them, is described today in the journal Nature in a paper by MIT professor Donald Sadoway, along with 15 other MIT collaborators and to China, Canada, Kentucky and Tennessee,” according to MIT News. The caveat with this new kind of battery is that it requires a lot of molten salts that have to be “close to the boiling point of water.” From the report: In their experiments, the team showed that the battery cells can withstand hundreds of cycles at exceptionally high charging rates, with a projected cost per cell of about one-sixth that of comparable lithium-ion cells. They showed that the charging rate is highly dependent on the operating temperature, with 110 degrees Celsius (230 degrees Fahrenheit) showing a rate 25 times faster than 25 C (77 F). Surprisingly, molten salt, which the team chose as an electrolyte simply because of its low melting point, turned out to be an accidental advantage. One of the biggest problems in battery reliability is the formation of dendrites, which are narrow metal spikes that accumulate on one electrode and eventually grow across to contact the other electrode, causing a short circuit and reducing efficiency. But it is this salt that happens to prevent this failure very well. The chloroaluminate salt they chose “essentially killed those runaway dendrites and allowed for very fast charging,” Sadoway says. “We ran experiments at very high charging rates, charging in less than a minute, and we never lost any cells due to dendrite shorting.”
Moreover, no external heat source is required to maintain the battery’s operating temperature. Heat is naturally produced electrochemically when charging and discharging a battery. “When you charge, you give off heat, and that keeps the salt from freezing. And then when you discharge, it also generates heat,” says Sadovey. For example, in a typical setup used for load balancing in a solar power plant, “you store electricity when the sun is shining, and then you withdraw electricity after dark, and you would do that every day. And this charge-idle-discharge-idle enough to generate enough heat to maintain the temperature.” This new battery lineup, he said, would be ideal for an installation the size needed to power a single home or small to medium-sized business, producing on the order of several tens of kilowatt-hours of capacity.
For larger plants, ranging from tens to hundreds of megawatt-hours, other technologies may be more efficient, including the liquid-metal batteries Sadovay and his students developed several years ago, which served as the basis for Ambri, a company that hopes to deliver its the first products within the next year. Sadovei was recently awarded this year’s European Inventors Award for this invention. The smaller size of aluminum-sulfur batteries will also make them practical for use in, for example, charging stations for electric vehicles, Sadoway says. He notes that when electric vehicles become so common on the road that several cars want to charge at once, as is the case today with gasoline fuel pumps, “if you try to do that with batteries and you want fast charging, the amperage is just so high that we don’t have that much amperage in the line powering the facility.” So having a battery system like this to store energy and release it quickly when needed could eliminate the need to install expensive new power lines to service these chargers. “The first it’s up to the company to demonstrate that it works at scale,” Sadoway says, and then put it through a series of stress tests, including hundreds of charge cycles.
If you’re looking for details on how this new battery works, we encourage you to check out Ars Technica’s article here.