Graphene is a relatively new technological development; after all, it was developed by the University of Manchester only in 2004, and it won the Nobel Prize in Physics in 2010. Nevertheless, it is a genuine multipurpose material, one with perhaps unprecedented potential. It has been used to develop water filtration devices, tough and flexible digital touchscreens, and advanced night vision contact lenses. Now, a team of researchers have found another use for it: creating incredibly powerful energy storage devices called microsupercapacitors. Their findings have been reported in the journal Advanced Materials.
Microsupercapacitors are somewhat similar to batteries, but they store and release energy at a far faster rate. Traditional capacitors absorb, retain and deposit their energy in the time it takes for a camera flash to occur; this is unlike common lithium-ion batteries, which store chemical energy almost indefinitely until it is slowly converted into electrical energy on demand.
The difference between a capacitor and a supercapacitor is essentially how much charge it can retain. Supercapacitors typically store around 10 to 100 times the amount of energy than regular capacitors of identical size. They are often used in electrical systems that require frequent rapid charge/discharge cycles, as opposed to long-term storage – in transportation, for example.
Graphene possesses, among many other things, an ability to conduct electricity over a wide range of temperatures rivalling that of copper – so it’s an ideal material to be used to build supercapacitors.
These new microsupercapacitors, developed by Rice University, represent a major technological advance in this field: they charge a remarkable 50 times faster than batteries, and discharge far slower than traditional capacitors. The amount of energy stored, and the speed in which they discharge their energy – a measure of power – matches that of commonly available commercial supercapacitors, and even approaches that of some lithium thin-film batteries. Their small size means they can be used in a wider range of electronic systems, including in wearable technology.
To manufacture these tiny components, the team of chemists and engineers used high-temperature carbon dioxide lasers to burn electrode patterns into plastic sheets at room-temperature air. At incredibly fast speeds, powerful beams almost instantaneously ignite the commercial polyimide plastic, removing everything but the carbon segment from the top layer. As this layer is only a few atoms thick, it represents a form of graphene – in this case called laser-induced graphene (LIG).
The LIG sheets were then treated with a variety of chemicals, which altered the graphene just enough to turn some into positive electrodes, and others into negative ones; together, these two sheet types form the dual components of a capacitor. Multiple additional components normally used to build conventional supercapacitors, such as binders or separators, were not required to build these microsupercapacitors.
“It's a pain in the neck to build microsupercapacitors now,” Rice University chemist and one of the authors of the paper, James Tour, said in a statement. “They require a lot of lithographic steps. But these we can make in minutes: We burn the patterns, add electrolyte and cover them.”
Quite literally, these microsuperconductors are created in a flash.
