Lithium sulfur: A battery revolution on the cheap?

Jun 04, 2014 by Michael Baum
Lithium sulfur battery revolution
Sulfur, often an industrial waste product, could be key to futre high-performance batteries. Credit: S_E-Fotolia_com

( —Whip together an industrial waste product and a bit of plastic and you might have the recipe for the next revolution in battery technology. Scientists from the National Institute of Standards and Technology (NIST), the University of Arizona in Tucson and Seoul National University in Korea have combined common ingredients to make an inexpensive, high-capacity lithium-sulfur battery that can be cycled hundreds of times without losing function.

The new battery's performance would be competitive in today's marketplace, says NIST materials scientist Christopher Soles. "Five hundred cycles with the capacity we've shown is definitely better than what's in your laptop today."

Batteries deliver power by shuttling positive ions between two electrodes—an anode and a cathode—while electrons travel around a circuit and do useful work. In the past decade, compact batteries using tiny lithium ions have achieved ever larger energy densities, packing more power in smaller volumes and helping to make smart phones and other mobile technologies ubiquitous. But lithium-ion batteries require bulky cathodes, typically made from ceramic oxides like cobalt oxide, to house the ions, which limits the battery's energy density. This means that for more power-intensive applications like long-range electric vehicles, even lithium-ion technology does not cut it.

Enter 's slimmer cousin, lithium-sulfur. These batteries' cathodes are made mainly of sulfur, a cheap waste product of petroleum processing. Sulfur weighs barely half as much as cobalt, atom for atom, and can pack more than twice as many lithium ions into a given volume as can cobalt oxide; thus, have several times the energy density of . But sulfur cathodes have two major weaknesses. Sulfur easily combines with lithium to form compounds that crystallize and gum up the battery's insides, and it tends to crack under the stress of repeated cycling. As a result, a typical lithium-sulfur battery becomes useless within a few dozen cycles—far too few for a laptop or car battery that may get cycled once a day for years.

To create a more stable cathode, the research team heated sulfur to 185 degrees Celsius, melting the element's eight-atom rings into long chains. They then mixed the sulfur chains with DIB, a carbon-based plastic precursor that links the sulfur chains together, creating what is known as a co-polymer. The team dubbed their manufacturing process "inverse vulcanization" because it resembles the process used to make rubber tires, with one crucial difference: In tires, carbon-containing material makes up the bulk, and sulfur is just sprinkled in.

Adding DIB to the cathodes prevents them from cracking as easily and keeps lithium-sulfur compounds from crystallizing. The scientists tested different mixtures of sulfur and DIB and found that the optimum mix contained between 10 and 20 percent DIB by mass: Less DIB did not provide the cathode-protecting properties while more of the electrochemically inactive DIB began to drag down the battery's .

The researchers ran their optimized battery through 500 cycles and found that it retained more than half its initial capacity. Other experimental lithium-sulfur batteries have performed similarly, but their cathodes require more complex manufacturing processes that would be expensive to scale up, says Jeffrey Pyun, a chemist at the University of Arizona and Seoul National University. By contrast, the team's polymer cathode requires only easily available materials and moderate heat. "We take it, we melt it in one step and pow, we get this plastic," Pyun says. "If you were to come to our lab, we could do this in five minutes."

Even so, we aren't likely to see lithium-sulfur batteries in stores right away. Soles notes that a commercial has to do more than just meet performance specs. For example, lithium can combust if exposed to air, so any commercial lithium- battery will need to undergo rigorous safety testing before it hits the market.

Explore further: Lithium-sulfur batteries last longer with nanomaterial-packed cathode

More information: A.G. Simmonds, J.J. Griebel, J. Park, K.R. Kim, W.J. Chung, V.P. Oleshko, J. Kim, E.T. Kim, R.S. Glass, C.L. Soles, Y-E. Sung, K. Char and J. Pyun. Inverse vulcanization of elemental sulfur to prepare polymeric electrode materials for Li−S batteries. ACS Macro Lett. 2014, 3, 229−232 DOI: 10.1021/mz400649w.

Related Stories

Battery development may extend range of electric cars

Jan 09, 2014

It's known that electric vehicles could travel longer distances before needing to charge and more renewable energy could be saved for a rainy day if lithium-sulfur batteries can just overcome a few technical ...

Recommended for you

Reliable systems for recharging electric vehicles

21 hours ago

The success of electric vehicle networks depends on economical vehicles – and efficient power grids. Existing power lines were not designed for the loads generated by electric vehicles. Fraunhofer researchers ...

Saving energy with smart facades

21 hours ago

Glass-fronted office buildings are some of the biggest energy consumers, and regulating their temperature is a big job. Now a façade element developed by Fraunhofer researchers and designers for glass fronts ...

Latin America divided between oil and green energy

Apr 01, 2015

Latin America spends billions of dollars subsidizing fossil fuels each year, but also has some of the world's largest renewable power programs, highlighting the energy-hungry region's divisions as it charts ...

User comments : 1

Adjust slider to filter visible comments by rank

Display comments: newest first

Jun 04, 2014
This comment has been removed by a moderator.
4.5 / 5 (8) Jun 04, 2014
Googling didn't help much with "DIB". Does anyone know what the compound is?

My google says: 1,3-diisopropenylbenzene (DIB)

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.