As the sales of electric vehicles skyrocketed in 2021, lithium, nickel, manganese and cobalt prices rose and we learned of the human and environmental costs of mining them. Now, a serendipitous discovery by scientists in Drexel’s College of Engineering promises to make sulfur batteries commercially viable and much longer lasting than lithium ion batteries.

These batteries would last more than 4,000 recharges – the equivalent of 10 years of use – and “improve the performance of batteries in electric vehicles and mobile devices in a commercially viable way,” said Vibha Kalra, PhD, of Drexel’s Department of Chemical and Biological Engineering, who led the research.

The battery industry has long dreamed of developing a commercially viable sulfur battery. Sulfur is naturally abundant and collecting it is safe and environmentally friendly – and its chemical structure allows it to store a lot of energy. But there have been obstacles.

So what does this serendipitous discovery mean? Freethink explains:

“these batteries will weigh a third of the equivalent lithium-ion batteries and have twice their lifespan! That means much faster, more efficient EVs with ranges of thousands miles will be commercially viable at a similar cost to today’s EVs. What’s more, they would actually still be useful in 10 years time, dramatically reducing waste and increasing the rate of EV adoption.

Furthermore, short-haul flights, cargo vessels, and passenger ferries will have a technology that will allow them to go fully electric. The weight-saving, long life, and competitive price will mean these sectors can finally achieve their low-carbon goals. 

In short, lithium-sulfur batteries could allow a huge range of activities to go electric, making net-zero emissions far more feasible.”

It also has implications for the environment. For one thing, we wouldn’t need to extract cobalt, nickel and manganese, which are limited and cause health and environmental hazards when they’re extracted. “Sulfur, on the other hand is found everywhere in the world, and exists in vast quanties in the United States because it is a waste product of petroleum production.”

Here’s Drexel’s explanation of the team’s serendipitous discovery:

“So, in hopes of eliminating polysulfide formation to avoid the adverse reactions, the team attempted to confine sulfur in the carbon nanofiber cathode substrate using a vapor deposition technique. While this process did not succeed in embedding the sulfur within the nanofiber mesh, it did something extraordinary, which revealed itself when the team began to test the cathode.

“As we began the test, it started running beautifully – something we did not expect. In fact, we tested it over and over again – more than 100 times — to ensure we were really seeing what we thought we were seeing,” Kalra said. “The sulfur cathode, which we suspected would cause the reaction to grind to a halt, actually performed amazingly well and it did so again and again without causing shuttling.”

Upon further investigation, the team found that during the process of depositing sulfur on the carbon nanofiber surface — changing it from a gas to a solid — it crystallized in an unexpected way, forming a slight variation of the element, called monoclinic gamma-phase sulfur. This chemical phase of sulfur, which is not reactive with the carbonate electrolyte, had previously only been created at high temperatures in labs and has only been observed in nature in the extreme environment of oil wells.

“At first, it was hard to believe that this is what we were detecting, because in all previous research monoclinic sulfur has been unstable under 95 degrees Celsius,” said Rahul Pai, a doctoral student in the Department of Chemical and Biological Engineering and coauthor of the research. “In the last century there have only been a handful of studies that produced monoclinic gamma sulfur and it has only been stable for 20-30 minutes at most. But we had created it in a cathode that was undergoing thousands of charge-discharge cycles without diminished performance — and a year later, our examination of it shows that the chemical phase has remained the same.”

After more than a year of testing, the sulfur cathode remains stable and, as the team reported, its performance has not degraded in 4,000 charge-discharge cycles, which is equivalent to 10 years of regular use. And, as predicted, the battery’s capacity is more than three-fold that of a Li-ion battery.

“While we are still working to understand the exact mechanism behind the creation of this stable monoclinic sulfur at room temperature, this remains an exciting discovery and one that could open a number of doors for developing more sustainable and affordable battery technology,” Kalra said.”

Freethink says that the team is already looking into using the breakthrough to make sodium-sulfur batteries which, by removing the need for lithium, would make batteries more eco-friendly and allow EV adoption to continue at breakneck speeds. “This accidental discovery at Drexel is set to revolutionise the world’s power usage and help humanity transition toward a cleaner, carbon-neutral society. Let’s just hope the team at Drexel can get this technology out of the lab and into our hands soon.”

Sources:

Breakthrough in cathode chemistry clears path for lithium-sulfur batteries’ commercial viability. Drexel News, Feb. 10, 2022.

An accidental discovery could change the world. Freethink, Apr. 15, 2022. 

Followups:

Natron to launch mass-production of long-life sodium-ion batteries. Inceptive Mind, May 10, 2022