Cheap aluminum-sulfur battery to store solar and wind energy

As the presence of solar and wind power plants increases in the world, the need for cheap, efficient and large capacity surplus energy storage systems grows. Having batteries capable of doing this job, it will be possible to maintain the solar and wind power supply even at night and when the wind is not blowing.

Current lithium ion batteries are still too expensive for most of these cases. Other options, such as pumping water to an elevated site so that it is then slowly released to power a hydroelectric turbine, require specific topography that is not always available.

Now, the international team of Donald Sadoway, a professor at the Massachusetts Institute of Technology (MIT) in the United States, has developed a new type of battery, made entirely of abundant and cheap materials, that could help fill that gap.

The new battery uses aluminum for one of the electrodes and sulfur for the other. As electrolyte between both electrodes, it uses a molten salt.

Aluminum is the most abundant metal on Earth. As for sulfur, it is cheaper than many other candidates the research team thought of. For all these reasons, these chemical elements are not only compatible to work each one in an electrode of the same battery, but they also constitute the most economical option.

In addition to being expensive, lithium-ion batteries contain a flammable electrolyte.

For the electrolyte between the two electrodes, Sadoway and his colleagues were clear that they didn’t want to use flammable, volatile organic liquids like those that have sometimes caused dangerous fires in cars and other lithium-ion battery-powered devices.

They ended up choosing a molten salt, which melts at a relatively low temperature, close to the boiling point of water, a much better option than other salts that melt at temperatures of hundreds of degrees Celsius.

All three ingredients are ultimately cheap and easy to find on the market. Aluminum, the same as the paper we buy at the supermarket to wrap sandwiches; sulfur, which is often a waste product from processes such as oil refining; and abundant and easy to acquire salts. And in addition to being cheap, the set is safe; it cannot catch fire, unlike the components of other batteries, as Sadoway emphasizes.

The three main components of the cell are aluminum (left), sulfur (middle), and the salt to be melted (right). (Image: Rebecca Miller. CC BY-NC-ND 3.0)

In their experiments, the team showed that the battery cells could withstand hundreds of cycles at exceptionally high charging rates, with a projected cost per cell about one-sixth that of comparable lithium-ion cells. They showed that charging speed was highly dependent on working temperature, with 110 degrees Celsius showing speeds 25 times faster than a temperature of 25 degrees Celsius.

An added bonus of the molten salt the team chose as an electrolyte is that it solves one of the biggest problems in battery reliability: dendrite formation. These are narrow spikes of metal that build up on one electrode and eventually grow into contact with the other electrode, causing a short circuit and eventually causing the battery to stop working. This salt removes the dendrites and allows a very fast and smooth recharge. Sadoway and his colleagues experimented with very high reload speeds, allowing a full reload in less than 1 minute, and never ran into a failure.

Sadoway’s team exposes the technical details of their new class of batteries in the academic journal Nature, under the title “Fast-charging aluminum-chalcogen batteries resistant to dendritic shorting.” (Font: NCYT by Amazings)