While the demand for ever-smaller electronic devices has spurred the miniaturization of a variety of technologies, one area has lagged behind in this downsizing revolution: energy-storage units, such as batteries and capacitors.
Now, Richard Kaner, a member of the California NanoSystems Institute at UCLA and a professor of chemistry and biochemistry, and Maher El-Kady, a graduate student in Kaner's laboratory, may have changed the game.
The UCLA researchers have developed a groundbreaking technique that uses a DVD burner to fabricate micro-scale graphene-based supercapacitors — devices that can charge and discharge a hundred to a thousand times faster than standard batteries. These micro-supercapacitors, made from a one-atom–thick layer of graphitic carbon, can be easily manufactured and readily integrated into small devices such as next-generation pacemakers.
The new cost-effective fabrication method, described in a study published this week in the journal Nature Communications, holds promise for the mass production of these supercapacitors, which have the potential to transform electronics and other fields.
"The integration of energy-storage units with electronic circuits is challenging and often limits the miniaturization of the entire system," said Kaner, who is also a professor of materials science and engineering at UCLA's Henry Samueli School of Engineering and Applied Science. "This is because the necessary energy-storage components scale down poorly in size and are not well suited to the planar geometries of most integrated fabrication processes."
"Traditional methods for the fabrication of micro-supercapacitors involve labor-intensive lithographic techniques that have proven difficult for building cost-effective devices, thus limiting their commercial application," El-Kady said. "Instead, we used a consumer-grade LightScribe DVD burner to produce graphene micro-supercapacitors over large areas at a fraction of the cost of traditional devices. Using this technique, we have been able to produce more than 100 micro-supercapacitors on a single disc in less than 30 minutes, using inexpensive materials."
The process of miniaturization often relies on flattening technology, making devices thinner and more like a geometric plane that has only two dimensions. In developing their new micro-supercapacitor, Kaner and El-Kady used a two-dimensional sheet of carbon, known as graphene, which only has the thickness of a single atom in the third dimension.
Kaner and El-Kady took advantage of a new structural design during the fabrication. For any supercapacitor to be effective, two separated electrodes have to be positioned so that the available surface area between them is maximized. This allows the supercapacitor to store a greater charge. A previous design stacked the layers of graphene serving as electrodes, like the slices of bread on a sandwich. While this design was functional, however, it was not compatible with integrated circuits.
In their new design, the researchers placed the electrodes side by side using an interdigitated pattern, akin to interwoven fingers. This helped to maximize the accessible surface area available for each of the two electrodes while also reducing the path over which ions in the electrolyte would need to diffuse. As a result, the new supercapacitors have more charge capacity and rate capability than their stacked counterparts.
Interestingly, the researchers found that by placing more electrodes per unit area, they boosted the micro-supercapacitor's ability to store even more charge.
Kaner and El-Kady were able to fabricate these intricate supercapacitors using an affordable and scalable technique that they had developed earlier. They glued a layer of plastic onto the surface of a DVD and then coated the plastic with a layer of graphite oxide. Then, they simply inserted the coated disc into a commercially available LightScribe optical drive — traditionally used to label DVDs — and took advantage of the drive's own laser to create the interdigitated pattern. The laser scribing is so precise that none of the "interwoven fingers" touch each other, which would short-circuit the supercapacitor.
"To label discs using LightScribe, the surface of the disc is coated with a reactive dye that changes color on exposure to the laser light. Instead of printing on this specialized coating, our approach is to coat the disc with a film of graphite oxide, which then can be directly printed on," Kaner said. "We previously found an unusual photo-thermal effect in which graphite oxide absorbs the laser light and is converted into graphene in a similar fashion to the commercial LightScribe process. With the precision of the laser, the drive renders the computer-designed pattern onto the graphite oxide film to produce the desired graphene circuits."
"The process is straightforward, cost-effective and can be done at home," El-Kady said. "One only needs a DVD burner and graphite oxide dispersion in water, which is commercially available at a moderate cost."
The new micro-supercapacitors are also highly bendable and twistable, making them potentially useful as energy-storage devices in flexible electronics like roll-up displays and TVs, e-paper, and even wearable electronics.
The researchers showed the utility of their new laser-scribed graphene micro-supercapacitor in an all-solid form, which would enable any new device incorporating them to be more easily shaped and flexible. The micro-supercapacitors can also be fabricated directly on a chip using the same technique, making them highly useful for integration into micro-electromechanical systems (MEMS) or complementary metal-oxide-semiconductors (CMOS).
These micro-supercapacitors show excellent cycling stability, an important advantage over micro-batteries, which have shorter lifespans and which could pose a major problem when embedded in permanent structures — such as biomedical implants, active radio-frequency identification tags and embedded micro-sensors — for which no maintenance or replacement is possible.
As they can be directly integrated on-chip, these micro-supercapacitors may help to better extract energy from solar, mechanical and thermal sources and thus make more efficient self-powered systems. They could also be fabricated on the backside of solar cells in both portable devices and rooftop installations to store power generated during the day for use after sundown, helping to provide electricity around the clock when connection to the grid is not possible.
"We are now looking for industry partners to help us mass-produce our graphene micro-supercapacitors," Kaner said.
University of California - Los Angeles: http://www.newsroom.ucla.edu
This press release was posted to serve as a topic for discussion. Please comment below. We try our best to only post press releases that are associated with peer reviewed scientific literature. Critical discussions of the research are appreciated. If you need help finding a link to the original article, please contact us on twitter or via e-mail.
Pigs ‘edited’ with a warthog gene to resist African swine fever could help spawn GM animal farms in the UK
Mouse House to make naturalist biopic, six years after box-office failure of Creation, starring Paul Bettany
International team spends 10 years making inroads into treatment of bacterium which kills up to half of those it infects
You may not know it, but you probably have some Neanderthal in you. For people around the world, except sub-Saharan Africans, about 1 to 3 percent of their DNA comes from Neanderthals, our close cousins who disappeared roughly 39,000 years ago.
Research at Yale plotted what happened in the brains of two scientists as they held a conversation
From medicines to jet fuel, we have so many reasons to celebrate the microbes we live with every day
Genome sequencing indicates Kennewick Man is Native American, reopening the bitter battle over whether he should be reburied or studied
In the article on the discovery of dinosaurs (They’re back, Review, 6 June) you state: “In Sussex, a local doctor uncovered fragmentary remains of what appeared to be two more species of colossal extinct land reptiles.” You grossly underplay the contribution of Lewes-born Gideon Mantell, geologist and palaeontologist, author and diarist, friend to princes and international scholars as well as local doctor. Mantell not only discovered (aided by his wife) the first remains of the iguanodon in 1824 but named it – as it resembled the tooth of an iguana. This was the first known land dinosaur, Mary Anning having identified the first sea-living dinosaur.Mantell went on to put together more pieces of the jigsaw with extra fossil discoveries. In contrast to Richard Owen, whose models form the basis for the Crystal Palace dinosaurs, Mantell stated correctly that iguanodon would have walked on their back legs, using their forearms to fight or gather food. He did, however, attribute the thumb spike to a nose horn though later corrected this assumption. The Natural History Museum has a display on Gideon and his wife Mary’s contribution as well as the large “Mantell-piece” of Iguanodon fossils that he had on show in his museum in Brighton. He sold it, along with many more priceless items, to the British Museum in 1838. Gideon Mantell’s reputation deserves better than your throwaway remark. Debby MatthewsLewes, East Sussex Continue reading...
Unique triangular hairs help keep Saharan silver ants cool at 70°C by manipulating the physics of light
Most animals wouldn't confront a fearsome predator like a lion. But through sophisticated group work, hyenas launch successful raids