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Graphene The Missing Link In Lithium-Air Battery Technology?

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The Graphene Carbon Lattice

The Graphene Carbon Lattice

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With so many different technologies vying to be the "next big thing" with electric car batteries, the law of averages dictates that at least one of those genuinely will be the next big thing.

The latest "next big thing" is graphene lithium-air batteries according to Talking Points Memo, and they're currently being tested by the Department of Energy's Pacific Northwest National Laboratory and Princeton University.

The science of graphene

Graphene was probably one of the most significant inventions of 2011. It's essentially a honeycomb sheet of linked carbon atoms, that's only a single atom thick.

If that's hard to picture, imagine using a graphite pencil to draw a solid shape on a piece of paper. That shape would be made of thousands of layers of carbon. Peel away those layers, one by one, and eventually you'd be left with a layer only one atom thick - that's basically what graphene is. It's a truly 2-dimensional material.

One of carbon's physical properties is good electrical conductivity, and this is what makes it attractive for use in batteries, specifically as a cathode.

Typical lithium-ion batteries, common in many electric cars as well as phones, laptops and all manner of other electrical devices, use a metal and oxygen cathode, a carbon anode and a lithium salt electrolyte.

A lithium air battery uses a pure lithium anode and carbon cathode. That cathode needs to be porous, and an atom-thick layer of carbon - as in graphene - is perfect for that brief.

The benefits

Graphene is porous, incredibly strong and very electrically conductive. It's already being considered as a high-strength material for structural use in cars.

Early tests have shown greater energy storage capacity than ever before, at 15,000 milliamp hours per gram (mAh/g). Lithium-ion manages only one hundredth of that storage capacity.

This means that theorectically, an absolutely tiny graphene lithium-air battery would be required to match current lithium-ion batteries, and larger batteries could offer far greater range than current electric cars muster. Of course, the technology would also be useful across the battery-powered spectrum.

Challenges

There are problems to overcome. Normal, 2D graphene struggles to let through a free flow of air molecules in the battery's cell, so the teams have developed a 3D, hole-filled sheet that works much more effectively.

Pure lithium is also extremely sensitive to water vapor, as found in large quantities in normal air. So sensitive, it can explode. An industrial membrane from DuPont is being tested to reduce humidity levels in the cell.

More work also needs to be done into rechargability, lifetime and power rate, but materials scientist Jie Xiao at the Pacific Northwest lab sees big things for the technology.

“Many groups are aggressively researching metal-air batteries and we believe this to be a promising technology for future use in fuel-efficient vehicles and also in stationary (power grid) applications".
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