Graphene promises a better way to power electric cars
Supercapacitors with big storage capacity could be woven into the fabric of a vehicle. Phil Dooley reports.
The next generation of electric cars may have their power sources neatly woven into the fabric of the chassis or bodywork, rather than heavy batteries that are slow to charge.
Yuan Chen and his team from Nanyang Technical University in Singapore have mixed graphene and carbon nanotubes to make a long, thin fibre, about the thickness of a human hair, that functions as a high power-density supercapacitor. The fibre could be woven into a flexible fabric that could be incorporated into any electricity-hungry gadget.
Supercapacitors, like batteries, can store electricity, soaking up charge on pairs of carbon plates. Unlike batteries, they charge in a matter of seconds and can release all their energy in a huge surge if needed. But their storage capacity is puny compared to batteries. Something that combined the features of supercapacitors and batteries would be revolutionary. “A supercapacitor with energy density comparable with a battery cell is really the holy grail,” says physicist Stephen Bosi from University of New England in New South Wales.
In an attempt to create such a supercapacitor, Chen turned to graphene. He knew these single-atom-thick sheets of carbon had great electricity storage potential because of the huge number of electron parking sites available in their large surface areas relative to their mass. “Graphene has a very high capacitance if exposed,” he says. The problem is that sheets of graphene pack together at high density, blocking charge from getting inside.
Chen overcame the packing problem by using highly conductive carbon nanotubes as spacers laid lengthways between the graphene layers. “The nanotubes are a network which transfers the charge quickly and the graphene provides the large surface area. These two things combine to give us the performance,” explains Chen.
The fibre supercapacitor showed an energy storage capacity of around 6.3 milliwatt hours per cubic centimetre of material. That’s about 10 times higher than commercial supercapacitors, and comparable with current lithium thin-film batteries. It’s still below the capacity of electric car batteries, but it’s a “promising step up”, says Bosi.
He sees broad potential applications for the technology. “Flexible electronics is going to be an absolute boon. It will mean you can stick electronics into environments that currently you can’t, or roll them up and put them in your pocket,” he says. “It’s hard to imagine an application they wouldn’t be useful for.”