Unlike today’s rechargeable batteries, which sip up energy over several hours, supercapacitors are energy storage devices that can charge and discharge within seconds and have huge potential to transform the way future electronics are powered.
Now scientists have figured out how to make supercapacitors from certain hemp fibers — and they can hold as much energy as the current top contender: graphene. They’re presenting their research, which a Canadian start-up company is working on scaling up, at the 248thNational Meeting & Exposition of the American Chemical Society (ACS), the world’s largest scientific society.
“Our device’s electrochemical performance is on par with or better than graphene-based devices,” says David Mitlin, Ph.D., “The key advantage is that our electrodes are made from biowaste using a simple process, and therefore, are much cheaper than graphene.” The fibers his team uses comes from the inner bark of the plant and often are discarded from Canada’s fast-growing industries that use hemp for clothing, construction materials and other products. .
Scientists had long suspected there was more value to the hemp bast — it was just a matter of finding the right way to process the material: “We’ve pretty much figured out the secret sauce of it,” says Mitlin, who’s now with Clarkson University in New York. “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.”
His team found that if they heated the fibers for 24 hours at a little over 350 degrees Fahrenheit, and then blasted the resulting material with more intense heat, it would exfoliate into carbon nanosheets.
Mitlin’s team built their supercapacitors using the hemp-derived carbons as electrodes and an ionic liquid as the electrolyte. Fully assembled, the devices performed far better than commercial supercapacitors in both energy density and the range of temperatures over which they can work. The hemp-based devices yielded energy densities as high as 12 Watt-hours per kilogram, two to three times higher than commercial counterparts. They also operate over an impressive temperature range, from freezing to more than 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.”
Source: American Chemical Society