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Hemp beats out graphene for high-performance energy storage

14 August 2014, 12:14 pm EDT By Rebecca Kaplan Tech Times
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Scientists have discovered a new way to use hemp fibers to create electrodes that can more efficiently fuel supercapacitors than graphene, what was previously thought to be the top contender.  ( )

Hemp could be a better battery material than the traditional graphene, scientists show in a new research study. Hemp is coming back into fashion, being used for everything from recyclable, good-for-the-environment cloth to vegan protein powders and milk substitutes.

In addition to that, scientists have now discovered that hemp can store as much energy as graphene, the material that scientists have long thought would be the ideal material for a new kind of super-battery known as a supercapacitor.

The team is going to show their findings at the 248th National Meeting and Exposition of the American Chemical Society (ACS). The meeting is being held at the ACS in San Francisco, where it will be shown through Thursday. There are going to be almost 12,000 scientific presentations at the meeting.

Supercapacitors are a new technology that is something like super-powered rechargeable batteries. They can charge in a very short time, in seconds. However, scientists haven't figured out yet how to make supercapacitors that can store the same amount of energy that traditional rechargeable batteries can. They have less energy density. Researchers are trying to make supercapacitors that can store more energy by improving the design of electrodes. David Mitlin, Ph.D. and a team of scientists have learned how to make an electrode that may be more cost effective and just as powerful as graphene, using hemp fibers.

"Our device's electrochemical performance is on par with or better than graphene-based devices," Mitlin says. "The key advantage is that our electrodes are made from biowaste using a simple process, and therefore, are much cheaper than graphene."

Scientists have been trying to figure out how to make a better supercapacitor with graphene, a durable but light carbon-based material that is also very thin and can be used to make electrodes. Scientists have been trying to work graphene into all kinds of new technology, like better solar powered batteries, touch-screens, and batteries. However, graphene is very costly while hemp is much cheaper.

Mitlin's research team set out to see if they could use hemp bast fibers to make a material similar to graphene. Hemp bast fibers are often a waste product from Canadian factories that turn hemp into cloth and other construction materials. No one had thought of an ideal way to process the bast fibers yet.

"We've pretty much figured out the secret sauce of it," says Mitlin. "The trick is to really understand the structure of a starter material and to tune how it's processed to give you what would rightfully be called amazing properties."

Mitlin's group discovered that by heating the hemp fibers for 24 hours and then heating them at a very high temperature, it would shed carbon nanosheets very similar to graphene.

The researchers then made supercapacitors using these hemp-based nanosheets as electrodes. They found that these supercapacitors worked much better than supercapacitors made of graphene electrodes in energy density and durability to different temperatures. The hemp batteries produced energy densities at least twice as high as graphene batteries. They are functional at any temperature from freezing to 200 degrees Fahrenheit.

"We're past the proof-of-principle stage for the fully functional supercapacitor," he says. "Now we're gearing up for small-scale manufacturing."

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