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Wearable supercapacitor chalks up high energy density

Posted: 14 May 2014 ?? ?Print Version ?Bookmark and Share

Keywords:supercapacitor? wearable? grapheme? battery?

A collaboration between researchers in Singapore, China, and the U.S. has yielded what is claimed as a fibre supercapacitor that can be stitched into garments and power wearable medical monitors and communication tools.

The device loads an interconnected network of graphene and carbon nanotubes so tightly that it stores energy comparable to some thin-film lithium batteries. The researchers believe the device's volumetric energy density is the highest reported for carbon-based microscale supercapacitors to date6.3microwatt-hours per cubic millimetre.

The device also maintains the advantage of charging and releasing energy much faster than a battery. The fibre-structured hybrid materials offer accessible surface areas and are highly conductive.

The researchers have developed a way to continuously produce the flexible fibre, enabling them to scale up production for a variety of uses. To date, they've made 50m-long fibres, and see no limits on length.

The fibre supercapacitor is envisioned as something that could be woven into clothing to power medical devices for people at home, or communications devices for soldiers in the field. The fibre could also be used as a space-saving power source and serve as 'energy-carrying wires' in medical implants.

Yuan Chen, a professor of chemical engineering at NTU led the new study, working with Dingshan Yu, Kunli Goh, Hong Wang, Li Wei and Wenchao Jiang at NTU; Qiang Zhang at Tsinghua; and Liming Dai at Case Western Reserve. The scientists report their research in Nature Nanotechnology.

Dai, a professor of macromolecular science and engineering at Case Western Reserve and a co-author of the paper, explained that most supercapacitors have high power density but low energy density, which means they can charge quickly and give a boost of power, but don't last long. Conversely, batteries have high energy density and low power density, which means they can last a long time, but do not deliver a large amount of energy quickly.

By mass, supercapacitors might have comparable energy storage, or energy density, to batteries. But because they require large amounts of accessible surface area to store energy, they have always lagged badly in energy density by volume.

The fibre is produced from a solution containing acid-oxidised single-wall nanotubes, graphene oxide and ethylenediamine, which promotes synthesis and dopes graphene with nitrogen, is pumped through a flexible narrow reinforced tube called a capillary column and heated in an oven for six hours.

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