Researchers at Rice University have turned their recently developed method of producing laser-induced graphene to the production of supercapacitors. The resulting energy-storage devices could eventually find use in flexible and wearable electronics.
In the litany of research projects that has applied graphene to supercapacitors, one thing has begun to emerge: You better not look to graphene to boost the storage capacity.
So far using graphene as a replacement for activated carbon on the electrodes of supercapacitors has fallen short of expectations, at least in terms of boosting capacity. It seems that graphene-based electrodes don’t enable energy storage much better than activated carbon, but because they can operate at higher frequencies than most supercapacitors and can be given shape and structures unavailable to other electrode materials, they remain a promising alternative.
It is this ability to create structures with the graphene-based supercapacitors and the material’s flexibility that is so attractive to the Rice researchers.
"What we've made are comparable to microsupercapacitors being commercialized now, but our ability to put devices into a 3-D configuration allows us to pack a lot of them into a very small area," said James Tour, who led the research, in a press release. "We simply stack them up.”
In research published in the journal Applied Materials and Interfaces, the Rice team employed a method they developed last year, dubbed laser-induced graphene (LIG). LIG involves firing a laser at an inexpensive polymer until all the elements except carbon are burned off, leaving a film of porous graphene.
Researchers at the California NanoSystems Institute (CNSI) at UCLA demonstrated in August of last year how effective a porous graphene can be as supercapacitor electrodes.
What makes the Rice team’s LIG so attractive is how easy it is to produce. “...we’re doing this very simply. Nothing about the process requires a clean room,” said Tour in the release. “It’s done on a commercial laser system, as found in routine machine shops, in the open air.”
Not only is the LIG easy to produce but it also seems to be pretty good at its job, according to the Rice researchers.
The researchers charged and discharged the devices for thousands of cycles with almost no loss of capacitance. In addition, the vertically-stacked supercapacitors showed almost no change in electrical performance when flexed, even after 8,000 bending cycles.
Tour noted: “We’ve demonstrated that these are going to be excellent components of the flexible electronics that will soon be embedded in clothing and consumer goods.”
Dexter Johnson is a contributing editor at IEEE Spectrum, with a focus on nanotechnology.