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Manufactured sulphur cathode allows up to 500 cycles

Posted: 09 Jun 2014 ?? ?Print Version ?Bookmark and Share

Keywords:lithium? sulphur cathode? battery?

Inverse vulcanisation

To create a more stable cathode, the research team heated sulphur to 185C, melting the element's eight-atom rings into long chains. They then mixed the sulphur chains with diisopropenylbenzene

(DIB), a carbon-based plastic precursor that links the sulphur chains together, creating what is known as a co-polymer. The team dubbed their manufacturing process "inverse vulcanisation" because it resembles the process used to make rubber tyres, with one crucial difference: In tyres, carbon-containing material makes up the bulk, and sulphur is just sprinkled in.

Adding DIB to the cathodes prevents them from cracking as easily and keeps lithium-sulphur compounds from crystallizing. The scientists tested different mixtures of sulphur and DIB and found that the optimum mix contained between 10 per cent and 20 per cent 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 energy density.

The researchers ran their optimised battery through 500 cycles and found that it retained more than half its initial capacity. Other experimental Li-S batteries have performed similarly, but their cathodes require more complex manufacturing processes that would be expensive to scale up, said 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 said. "If you were to come to our lab, we could do this in five minutes."

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

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