Aluminum-Sulphur Battery: A Low-Cost BackUp Storage for Renewable Energy Sources

Rapid growth in non-conventional power systems (solar and wind) has also raised the need for economical energy storage solutions to provide power during unsuitable weather conditions. The storage solutions based on Lithium-ion batteries do exist and are in use as well but these solutions aren’t economical for these applications. Additionally, the supply chain issues associated with Lithium, pose a challenge to the long-term use of Lithium based storage systems.

This problem could be solved soon, according to new research, published in Nature, by the collaboration of scientists at MIT and other institutes*. The researchers have developed a new concept battery made of abundant and cheap materials, aluminum, sulphur and rock salt crystals , as primary constituents. All of these are domestically available Earth-abundant materials which do away with the need for a global supply chain.

Professor Donald Sadoway, one of the researcher, had started browsing the periodic table looking for a cheap and Earth-abundant metals can substitute Lithium. Firstly, he rejected the commercially dominant metal, iron, as it doesn’t have the suitable electrochemical properties for an efficient battery. Then he zeroed in on Aluminum – the second-most-abundant metal in the marketplace and the most abundant metal on Earth, as one of the electrodes. In their quest for the other electrode to pair with Aluminum, the researchers decide on the cheapest of all the non-metals, i.e. sulphur.

As far as an electrolyte is considered, the group looked for the non-volatile and inflammable organic liquid to avoid dangerous fires frequently witnessed in Li-ion battery-based applications like cars etc. Firstly, they started with some polymers but later switched towards a variety of molten salts with relatively low melting points (close to the boiling point of water). “Once you get down to near body temperature, it becomes practical” to make batteries that don’t require special insulation and anticorrosion measures”, Prof. Sadoway says. The group finally ended up with three ingredients: aluminum, sulphur and rock salt. “The ingredients are cheap, and the thing is safe — it cannot burn,” Sadoway says.

Through the experiments, the researchers have shown that these battery cells could go through hundreds of cycles at exceptionally high charging rates, which depends on the working temperature. At 110 deg C the charging rate is 25 times faster than that at 25 deg C. Also, these cells cost one-sixth that of comparable lithium-ion cells.

Because of its low melting point, the salt has effectively prevented the formation of dendrites. It’s widely known that the formation of dendrites, narrow spikes of metal that build up on one electrode and eventually grow across to contact the other electrode, leads to short-circuit and hampers efficiency. “We did experiments at very high charging rates, charging in less than a minute, and we never lost cells due to dendrite shorting,” Sadoway says.

The group has also discovered that the battery naturally produces heat electrochemically by charging and discharging the battery, thus requiring no external heat source to maintain its operating temperature. As you charge, you generate heat, and that keeps the salt from freezing. And then, when you discharge, it also generates heat,” Sadoway says. Explaining its use in a typical load-levelling at a solar generation facility Sadoway continues, “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.”

For now, the researcher has suggested using the new battery formulation for installations needed to power a single home or small to medium business.

This new technology has already resulted in the start-up Avanti, co-founded by Prof. Sadoway. Avanti has also licensed the patents to the system. “The first order of business for the company is to demonstrate that it works at scale and then subject it to a series of stress tests, including running through hundreds of charging cycles,” Sadoway says.

*Peking University, Yunnan University and the Wuhan University of Technology, in China; the University of Louisville, in Kentucky; the University of Waterloo, in Canada and Argonne National Laboratory, in Illinois