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MIT Develops New Aluminum-Sulfur Battery Concept

As the world moves toward more sustainable power systems, such as wind and solar, there is a growing need for economical, large-scale battery backup systems that can provide power when sun and wind are blocked or unavailable. Lithium-ion batteries are the most common type of battery on the market. However, they are currently too expensive for most of these kinds of sustainable energy storage applications.

Researchers at the Massachusetts Institute of Technology (MIT) have developed a new battery concept, made entirely from abundant and inexpensive materials, that could help to meet this challenge. The development was achieved in cooperation with researchers from Oak Ridge National Laboratory and the University of Louisville in the U.S.; Peking University, Yunnan University, and the Wuhan University of Technology in China;  and the University of Waterloo in Canada. The work was supported by the MIT Energy Initiative, the MIT Deshpande Center for Technological Innovation, and ENN Group.

The new battery architecture uses aluminum and sulfur as 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 Donald Sadoway, who is the John F. Elliott Professor Emeritus of Materials Chemistry at MIT.  “The ingredients are cheap, and the thing is safe — it cannot burn.”

The three primary constituents of the new battery concept are all readily available materials that do not require a global supply chain (L-R): aluminum, sulfur, and rock salt crystals. (Photo: Rebecca Miller, MIT.)

When considering an alternative to lithium-ion batteries, Sadoway and his team had to consider whether the chemistry of the material would be suitable for batteries, as well as the material’s availability, cost, and flammability (since lithium-ion batteries contain a flammable electrolyte that can be hazardous for transportation applications). After exploring the periodic table of elements, the researchers found that aluminum (the most abundant metal on Earth) would be an ideal material for this purpose.

When considering what materials to pair the aluminum with (for the other electrode and electrolyte), the team needed to not only meet the previously mentioned requirements, but also ensure that they would work in conjunction with aluminum. Sulfur was selected as the other electrode material, since it is the cheapest of all the non-metal materials. Rock salt crystals (in the form of chloro-aluminate salt) were selected as the electrolyte, since they have the same boiling point as water and don’t require any special insulation and anticorrosion measures.

In addition, the battery concept requires no external heat source to maintain its operating temperature. The heat is naturally produced electrochemically by the charging and discharging of the battery. “As you charge, you generate heat, and that keeps the salt from freezing. And then, when you discharge, it also generates heat,” explained Sadoway. He noted for example that, in a typical installation used for load-leveling at a solar generation facility, “you’d store electricity when the sun is shining, and then you’d draw electricity after dark, and you’d do this every day. That charge-idle-discharge-idle is enough to generate enough heat to keep the thing at temperature.”

According to Sadoway, this new battery formulation, he says, would be ideal for solar and wind installations of about the size needed to power a single home or small-to-medium-sized business, producing on the order of a few tens of kilowatt-hours of storage capacity.

These smaller-scale aluminum-sulfur batteries would also be practical for uses such as electric vehicle charging stations. Sadoway pointed out that, when electric vehicles become common enough on the roads that several cars want to charge up at once, as happens today with gasoline fuel pumps, “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.” Therefore, having a battery system such as aluminum-sulfur batteries to store power and then quickly release it when needed could eliminate the need for installing expensive new power lines to serve these chargers.

Sadoway and Luis Ortiz have co-founded a new spinoff company called Avanti, which will further develop and market this new battery technology. “The first order of business for the company is to demonstrate that it works at scale,” said Sadoway. Following this, the company will subject the technology to a series of stress tests, including running it through hundreds of charging cycles.

The new battery architecture has been described in more detail within the paper, “Fast-charging aluminium–chalcogen batteries resistant to dendritic shorting,” written by Sadoway along with 15 other international colleagues. The paper was published in Nature.

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