May 19, 2009

Sulfur promises super batteries

Melt sulfur into nanoscale holes in porous carbon and you can dramatically increase lithium-ion battery capacity.

Lithium-ion battery electrodes made of carbon and sulfur have a theoretical capacity five times greater than the theoretical limit for today's lithium-ion electrode materials, but sulfur tends to leak from the electrodes.

An electrode made by melting sulfur into porous carbon holds onto its sulfur. The porous carbon consists of carbon nanorods separated by 3-nanometer channels containing carbon fibers that help hold the structure together. The fibers keep most of the sulfur from leaking out and also provide electrical contact to more of the sulfur. A polymer coating on the outside surface of the carbon also helps hold in the sulfur.

The plastic-coated carbon-sulfur electrode has a stable discharge capacity of 1,100 milliamp hours per gram, which is about six times that of today's best commercial lithium-ion batteries.

Recent research with crystalline silicon electrodes shows the potential for even higher storage capacities. Crystalline silicon is more expensive than porous carbon and sulfur.

Carbon-sulfur electrodes could be used in electric vehicles with extended ranges and storage systems for renewable energy sources like solar cells and wind turbines.

Research paper:
A highly ordered nanostructured carbon–sulphur cathode for lithium–sulphur batteries
Nature Materials, published online May 17, 2009

Researchers' contact:
Linda F. Nazar

Related stories and briefs:
Porous silicon boosts lithium batteries -- related research
Silicon nanowires boost batteries -- related research
Nested nanotubes promise better battery electrodes -- related research
Nano tin electrodes beat graphite -- related research

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