Researchers at the Queensland University of Technology (QUT) in Australia have developed a supercapacitor featuring graphene carbon nanotube films. They’re confident that their creation could dramatically boost the power and range of all-electric vehicles that now rely on lithium-ion (Li-ion) batteries for propulsion.
In research that was published in both the Journal of Power Sources and Nanotechnology, the Australian researchers used graphene films as the electrodes and carbon nanotube films as current collectors. The result was devices demonstrating energy densities ranging from 8 to 14 watt-hours per kilogram, and power densities between 250 and 450 kilowatts per kilogram.
The hope has been that someone could make graphene electrodes for supercapacitors that would boost their energy density into the range of chemical-based batteries. The supercapacitors currently on the market have on average an energy density around 28 Wh/kg, whereas a Li-ion battery holds about 200Wh/kg. That’s a big gap to fill.
The research in the field thus far has indicated that graphene’s achievable surface area in real devices—the factor that determines how many ions a supercapacitor electrode can store, and therefore its energy density—is not any better than traditional activated carbon. In fact, it may not be much better than a used cigarette butt.
Though graphene may not help increase supercapacitors’ energy density, its usefulness in this application may lie in the fact that its natural high conductivity will allow superconductors to operate at higher frequencies than those that are currently on the market. Another likely benefit that graphene will yield comes from the fact that it can be structured and scaled down, unlike other supercapacitor materials.
It is this ability to be molded into various shapes that the Australian researchers hope to exploit; they suggest that the supercapacitor films they have developed could be used to line parts of a car’s chassis to offer a quick energy boost to all-electric vehicles using Li-ion batteries.
"Vehicles need an extra energy spurt for acceleration, and this is where supercapacitors come in. They hold a limited amount of charge, but they are able to deliver it very quickly, making them the perfect complement to mass-storage batteries," said Marco Notarianni, a QUT researcher, in a press release.
Notarianni added: "Supercapacitors offer a high power output in a short time, meaning a faster acceleration rate of the car and a charging time of just a few minutes, compared to several hours for a standard electric car battery."
Graphene-based supercapacitors have been a bit of a disappointment to those who envisioned them completely replacing lithium-ion (Li-ion) batteries for powering all-electric vehicles. This latest complementary role suggested by the Australian researchers may be a way to see them put to some use.
However, it’s not clear that the energy density numbers achieved during this latest round of research have given us any reason to think that a graphene-based supercapacitor will be the route leading to an all-electric vehicle that operates solely on supercapacitors.
Dexter Johnson is a contributing editor at IEEE Spectrum, with a focus on nanotechnology.