The three primary constituents of the battery are aluminum (left), sulfur (center), and rock salt crystals (right). All are domestically available, Earth-abundant materials not requiring a global supply chain. (Image: Rebecca Miller via

In an increasingly solar world, the need is growing for economical, large-scale backup systems to provide power when the sun is down and the air is calm. Lithium-ion (Li-ion) batteries are too expensive, and other options — such as pumped hydro — require specific topography that’s not always available.

Now, researchers have developed a new kind of battery, made entirely from abundant, inexpensive materials — aluminum and sulfur are its two electrode materials, with a molten salt electrolyte in between.

“I wanted to invent something that was better, much better, than lithium-ion batteries for small-scale stationary storage, and ultimately for automotive [uses],” said MIT Professor Donald Sadoway, who is the John F. Elliott Professor Emeritus of Materials Chemistry.

Another flaw, Li-ion batteries contain a flammable electrolyte — not ideal for transportation. So, Sadoway studied the periodic table for cheap, Earth-abundant metals that might be able to sub for lithium. Iron, the commercially dominant metal, doesn’t have the right electrochemical properties for an efficient battery. However, the second-most-abundant metal in the marketplace — and the most abundant metal on Earth — fit the bill.

“So, I said, well, let’s just make that a bookend; it’s going to be aluminum,” said Sadoway.

Deciding what to pair the aluminum with for the other electrode was the next decision, followed by what kind of electrolyte to put in between to carry ions back and forth during charging and discharging. The cheapest of all the non-metals is sulfur, so that became the second electrode material. As for the electrolyte, “we were not going to use the volatile, flammable organic liquids,” Sadoway said.

The team 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, as opposed to nearly 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 anticorrosion measures, he said.

“The ingredients are cheap, and the thing is safe — it cannot burn,” said Sadoway.

Throughout its trials, the team proved that the battery cells could endure hundreds of cycles at exceptionally high charging rates, with a projected cost per cell of about one-sixth that of comparable Li-ion cells. It was also proved that the charging rate was highly dependent upon the working temperature, with 110 °C (230 °F) showing 25 times faster rates than 25 °C (77 °F).

The chosen molten salt turned out to have a fortuitous advantage, as one of the biggest problems in battery reliability is the formation of dendrites — narrow spikes of metal that build up on one electrode and eventually grow across to contact the other electrode. This causes a short-circuit and hampering efficiency.

The chloro-aluminate salt the team chose “essentially retired these runaway dendrites, while also allowing for very rapid charging,” Sadoway said. “We did experiments at very high charging rates, charging in less than a minute, and we never lost cells due to dendrite shorting.”

To boot, the battery requires no external heat source to maintain its operating temperature.

“As you charge, you generate heat, and that keeps the salt from freezing,” said Sadoway. “And then, when you discharge, it also generates heat. In a typical installation used for load-leveling at a solar generation facility, for example, you’d store electricity when the sun is shining, and then you’d draw electricity after dark, and you’d do this every day. And that charge-idle-discharge-idle is enough to generate enough heat to keep the thing at temperature.”

Sadoway noted that this new battery formulation would be ideal for installations of about the size needed to power a single home or small to medium business — the order of a few tens of kilowatt-hours of storage capacity. The smaller scale of the aluminum-sulfur batteries would also make them practical for electric vehicle charging stations.

Would a battery based on sulfur run the risk of producing the foul odors? No, according to Sadoway.

“The rotten-egg smell is in the gas, hydrogen sulfide,” he said. “This is elemental sulfur, and it’s going to be enclosed inside the cells.”

The research team included members from Peking University, Yunnan University, and the 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 work was supported by the MIT Energy Initiative, the MIT Deshpande Center for Technological Innovation, and ENN Group.

Here is a Q&A that Tech Briefs conducted with Professor Sadoway. (Edited for clarity)

Tech Briefs: What’s the next step in your research for this project?

Sadoway: I've moved from the lab at MIT to a startup company, Avanti Battery. And we’re now in the process of upscaling the technology to demonstrate that it can perform at scale. The goal of the research at MIT was to demonstrate the electrochemistry, and now that we’re convinced that the electrochemistry is sound we have to demonstrate that we can build batteries of some practical size.

Tech Briefs: When will this technology be commercialized?

Sadoway: Oh, you want me to predict the future? [laughs] The answer is some number of years. I wish I could tell you it's going to be some number of months, but I think the unit of time is years. Three years? Four years? Five years? I can't say.

To the extent that we can borrow from what we know about the manufacturing of lithium-ion batteries to the extent that any of that is transferable, then maybe that can shorten the development time. But this is not like writing code; this is tough tech, and it’s going to take some time.

Tech Briefs: Do you think there will be a large market for it? Will it catch on?

Sadoway: Oh, most definitely. The thing is cheaper than lithium-ion; with performance, certainly when it comes to charging speed, it’s far superior to lithium-ion and it cannot catch fire. The more lithium-ion-powered vehicles there are on the road, the more episodes we’re going to see with things catching fire and people are going to start saying, ‘When can we expect a safe battery?’

Then, of course, there are other applications for small-scale stationary storage where lithium-ion is just right off the bat a bad fit. And this can really fill that gap. So I'm confident that this thing will be not a solution looking for a problem but rather an answer to a question that people have been asking for a long time.