Original URL: http://www.theregister.co.uk/2013/06/06/ornl_boffins_suck_the_liquid_out_of_batteries/

Boffins develop 'practically free' sulphur-powered batteries

Scientists suck batteries dry

By Richard Chirgwin

Posted in Science, 6th June 2013 03:54 GMT

Scientists at Oak Ridge National Laboratory (ORNL) in the USA have demoed a battery technology that makes two radical departures from the past: the main material is the superabundant sulphur, and it's an all-solid battery without a liquid electrolyte.

Lithium-sulphur combinations have all the characteristics needed to create useful batteries – except longevity, and that's a major hurdle in materials science. Liquid electrolytes dissolve the lithium polysulphides, which helps carry ions around – but breaks down the anodes and cathodes in the battery.

That's because the sulphur needs to be dissolved when cycling a conventional lithium sulphide battery – it acts as a catholyte – and the dissolving of sulphur causes parasitic side reactions that destroy the battery.

What's needed, the researchers say, are materials that offer “high ionic conductivities and excellent electrochemical reversibility during battery cycling.”

To get rid of the liquid, the ORNL researchers worked on two materials. The first was a class of sulphur-rich materials whose ionic conductivity matches that of cathodes based on conventional lithium oxides.

The second is an all-solid electrolyte, using the sulphidophosphate compounds. The result is an ionically-conductive cathode that “enabled the ORNL battery to maintain a capacity of 1200 milliamp-hours (mAh) per gram after 300 charge-discharge cycles at 60 degrees Celsius. For comparison, a traditional lithium-ion battery cathode has an average capacity between 140-170 mAh/g.”

“This game-changing shift from liquid to solid electrolytes eliminates the polysulfide shuttle and enables stable cycling of metallic lithium anodes. With the emergence of solid electrolytes with ionic conductivities comparable to that of liquid electrolytes, all-solid-state Li-S batteries promise to be the next breakthrough for electric energy storage,” the researchers write.

And the best bit? "Sulphur is practically free," said lead researcher Chengdu Liang, lead author of the study published in Angewandte Chemie International Edition.

It's also safer than a liquid electrolyte – for example, with far less fire risk associated with a solid electrolyte. ®