The novel micro-supercapacitor based on laser-induced graphene developed by Rice University researchers. Photo: Tour Group/Rice University.
The novel micro-supercapacitor based on laser-induced graphene developed by Rice University researchers. Photo: Tour Group/Rice University.

Rice University researchers who pioneered the development of laser-induced graphene have configured their discovery into flexible, solid-state micro-supercapacitors that rival the best available for energy storage and delivery. Developed in the lab of Rice chemist James Tour, the new micro-supercapacitors are geared toward use in electronics and clothing, and are the subject of paper in Advanced Materials.

Micro-supercapacitors are not batteries, but inch closer to them as the technology improves. Traditional capacitors store and release energy quickly, in contrast to common lithium-ion batteries that take a long time to charge and release their energy as needed. Rice's micro-supercapacitors charge 50 times faster than batteries, discharge more slowly than traditional capacitors and match commercial supercapacitors for both the amount of energy stored and power delivered.

The micro-supercapacitors are manufactured by burning electrode patterns into plastic sheets using a commercial laser. Unlike the complex fabrication procedures that have limited the widespread application of micro-supercapacitors, this process can take place in the air, rather than a vacuum, and at room temperature. The researchers see a path toward cost-effective, roll-to-roll manufacturing.

"It's a pain in the neck to build micro-supercapacitors now," Tour said. "They require a lot of lithographic steps. But these we can make in minutes: we burn the patterns, add electrolyte and cover them."

With a capacitance of 934 microfarads per square centimeter and an energy density of 3.2 milliwatts per cubic centimeter, these micro-supercapacitors rival commercial lithium thin-film batteries, with a power density two orders of magnitude higher than batteries, the researchers claimed. The devices also displayed long life and mechanical stability when repeatedly bent 10,000 times.

The energy density of these micro-supercapacitors is down to laser-induced graphene (LIG). Tour and his group discovered last year that heating a commercial polyimide plastic sheet with a laser burned everything but carbon from the top layer, leaving a form of graphene. But rather than a flat sheet comprising hexagonal rings of carbon atoms, the laser left a spongy array of graphene flakes attached to the polyimide.

The researchers treated these LIG arrays – interdigitated like folded hands – with manganese dioxide, ferric oxyhydroxide or polyaniline through electrodeposition and turned the resulting composites into positive and negative electrodes. These composites could then be formed into solid-state micro-supercapacitors with no need for current collectors, binders or separators.

Tour is convinced the day is coming when supercapacitors replace batteries entirely, producing energy storage systems that charge in minutes rather than hours. "We're not quite there yet, but we're getting closer all the time," he said. "In the interim, they're able to supplement batteries with high power. What we have now is as good as some commercial supercapacitors. And they're just plastic."

This story is adapted from material from Rice University, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.