Graphene and carbon nanotubes combined to create flexible, wearable supercapacitor
May 15, 2014
An international team of researchers has developed a supercapacitor composed of graphene and carbon nanotubes that is claimed flexible enough to be woven into clothing and potentially powerful enough to offer a real alternative to batteries for use in portable devices. Capable of being charged and discharged in excess of 10,000 cycles, the new supercapacitor also promises to be significantly lighter, faster to charge, and more robust than current battery technology.
Researchers from Nanyang Technological University (NTU) in Singapore, Tsinghua University in Beijing, China, and Case Western Reserve University in Cleveland, Ohio, produced the supercapacitor by heating and bonding micro-scale graphene sheets and carbon nanotubes to form a continuous, interconnected network of filaments. The result is reported to be a complex hybrid fiber so densely packed that its capacitive surface area is a whopping 396 sq m (4,262 sq ft) per gram.
The researchers say that this results in a capacitance of 300 Farads per cubic centimeter, and a volumetric energy density of 6.3 microwatts per cubic millimeter which, in practical parlance, means that the newly-developed supercapacitor is comparable in power to a 4-volt, 500 microamp, thin film Lithium-ion battery. This is more than enough to run many currently available low-power devices, as well as electronic components such as LEDs.
The team has so far produced a 50 meter (164 ft) long set of interwoven fibers in a continuous melding process in the laboratory that yielded approximately 1 m (3 ft) per hour. It is expected that, scaled-up, this process could eventually see large quantities of supercapacitor fibers made on a commercial scale, bringing down the price and increasing its availability.
"The fiber supercapacitor continues to work without performance loss, even after ending hundreds of times," said researcher Dingshan Yu. So, when this supercapacitor material does become commercially viable, its ability to be bent continuously out of shape while maintaining its charge and structural integrity could lead to it being woven into clothing, backpacks, shoes, and other items to produce a wearable power system.
In turn, these could then power devices such as medical monitors, GPS devices or any of the other myriad accoutrements to our technological life that would allow us even more mobile freedom. It could also be woven into textiles for use by the military to power soldiers’ equipment, incorporated into other materials to form the case of a device that is also its power supply, or even double as the cover and the battery for an eReader.
But more than this, the low mass, high volumetric density of a graphene and carbon nanotube supercapacitor is so great that it may well provide a solution to a more pressing problem for electric vehicles: weight. At a mere fraction of the bulk of storage batteries, and capable of being charged and discharged for more than 10,000 cycles (less than 1,000 is the norm for rechargeable batteries), this type of superlight power storage could prove to be the answer to the electrical motor industry's prayers.
And, by taking advantage of its bendable nature, it could be so densely packed that many thousands of feet of charged supercapacitor material could be shoehorned into any number of spaces on a vehicle, no matter the shape, thereby freeing electric vehicle designers from the tyranny of having to find very large, very flat areas to house the batteries.
There's still more work to be done, but this new material promises to open up whole new avenues for incorporating electric storage devices as intrinsic components, rather than as separate adjuncts to devices.
The research was recently published in Nature.
Source: Case Western Reserve University