Optical Drive Etches Graphene Supercapacitors
LOS ANGELES, March 21, 2012 — The search for an optimal electrochemical capacitor has been held up by the need for an electrode with energy density comparable to that of a battery. A novel graphene-based electrode, produced with a standard LightScribe DVD optical drive, could solve that. The discovery could yield more advanced energy storage technology for portable electronics.
Electrochemical capacitors, also called ultracapacitors or supercapacitors, store higher amounts of charge than regular capacitors and have garnered attention as energy storage devices because they charge and discharge faster than batteries.
However, unlike batteries, they have been limited by low energy densities. Researchers have sought an electrochemical capacitor that combines a battery’s high energy density and a capacitor’s power performance.
Graphic demonstrating graphene’s ability to store electrical energy through the interaction with ions in an electrochemical capacitor (Image: © Science/AAAS)
Now, a research team from the University of California, Los Angeles, has developed high-performance electrochemical capacitors with graphene electrodes. The laser-scribed graphene (LSG) electrodes were produced by coating a DVD disc with graphite oxide and laser-treating it inside a LightScribe DVD drive.
The LightScribe laser reduces and exfoliates the graphite oxide while simultaneously producing electrodes with an open network structure. The LSGs have substantially higher and more accessible surface area, enabling a sizable charge storage capacity. The electrode’s open network structure reduces the electrolyte ions’ diffusion path, allowing a fast, high-power charge.
Evaluations of devices made using the LSGs demonstrate ultrahigh energy density values in various electrolytes, while the high power density and cycle stability of supercapacitors is retained.
“Our study demonstrates that our new graphene-based supercapacitors store as much charge as conventional batteries, but can be charged and discharged a hundred to a thousand times faster,” said Richard B. Kaner, a professor of chemistry and materials science and engineering at UCLA.
Schematic showing the structure of laser scribed graphene supercapacitors. (Image: UCLA)
The team replaced the liquid electrolyte and separator layers found in commercially available electrochemical capacitors with a polymer gel electrolyte that also acts as a separator, simplifying the device and decreasing it in size. It also eliminates the special packaging materials that liquid electrolytes require.
To test the solid-state device for flexible storage under real conditions, they placed it under constant mechanical stress and analyzed its performance. They found that it had almost no effect on the performance of the device.
“We attribute the high performance and durability to the high mechanical flexibility of the electrodes along with the interpenetrating network structure between the LSG electrodes and the gelled electrolyte,” Kaner said. “The electrolyte solidifies during the device assembly and acts like glue that holds the device components together.”
The work appeared in Science.
For more information, visit: www.cnsi.ucla.edu
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