A team of international researchers have created graphene supercapacitors using a LightScribe DVD burner. These capacitors are both highly flexible (pictured below) and have energy and power densities far beyond existing electrochemical capacitors, possibly within reach of conventional lithium-ion and nickel metal hydride batteries.
The team, which was led by Richard Kaner of UCLA, started by smearing graphite oxide — a cheap and very easily produced material — films on blank DVDs. These discs are then placed in a LightScribe drive (a consumer-oriented piece of gear that costs less than $50), where a 780nm infrared laser reduces the graphite oxide to pure graphene. The laser-scribed graphene (LSG) is peeled off and placed on a flexible substrate, and then cut into slices to become the electrodes. Two electrodes are sandwiched together with a layer of electrolyte in the middle — and voila, a high-density electrochemical capacitor, or supercapacitor as they’re more popularly known.
Now, beyond the novel manufacturing process — the scientists are confident it can be scaled for commercial applications, incidentally — the main thing about LSG capacitors is that they have very desirable energy and power characteristics. Power-wise, LSG supercapacitors are capable of discharging at 20 watts per cm3, some 20 times higher than standard activated carbon capacitors, and three orders of magnitude higher than lithium-ion batteries. Energy-wise, we’re talking about 1.36 milliwatt-hours per cm3, about twice the density of activated carbon, and comparable to a high-power lithium-ion battery.
These characteristics stem from the fact that graphene is the most conductive material known to man — the LSG produced by the scientists showed a conductivity of 1738 siemens per meter (yes, that’s a real unit), compared to just 100 siemens for activated carbon. The performance of capacitors is almost entirely reliant on the surface area of the electrodes, so it’s massively helpful that one gram of LSG has a surface area of 1520 square meters (a third of an acre). As previously mentioned, LSG capacitors are highly flexible, too, with no effect on its performance (pictured right).
These graphene supercapacitors could really change the technology landscape. While computing power roughly doubles every 18 months, battery technology is almost at a standstill. Supercapacitors, which suffer virtually zero degradation over 10,000 cycles or more, have been cited as a possible replacement for low-energy devices, such as smartphones. With their huge power density, supercapacitors could also revolutionize electric vehicles, where huge lithium-ion batteries really struggle to strike a balance between mileage, acceleration, and longevity. It’s also worth noting, however, that lithium-ion batteries themselves have had their capacity increased by 10 times thanks to the addition of graphene. Either way, then, graphene seems like it will play a major role in the future of electronics.
Read more at Science (paywalled)