Wearables and electric vehicles may get boost from boron-infused graphene

May 19, 2015

Rice University scientists made this supercapacitor with interlocked “fingers” using a laser and writing the pattern into a boron-infused sheet of polyimide. The device may be suitable for flexible, wearable electronics. (credit: Tour Group/Rice University)

Infusing the polymer in a laser-induced graphene supercapacitor (used to rapidly store and discharge electricity) with boric acid quadrupled the supercapacitor’s ability to store an electrical charge while greatly boosting its energy density (energy per unit volume), Rice University researchers have found.

The Rice lab of chemist James Tour uses commercial lasers to create thin, flexible supercapacitors by burning patterns into common polymers. The laser burns away everything but the carbon to a depth of 20 microns on the top layer, which becomes a foam-like matrix of interconnected graphene flakes.

Capacitors charge quickly and release their energy in a burst when needed, as in a camera flash. Supercapacitors add the high energy capacity of batteries and have potential for electric vehicles and other heavy-duty applications. But the potential to shrink them into a small, flexible, easily produced package could make them suitable for many more applications, including catalysts, field emission transistors, and components for solar cells and lithium-ion batteries, the researchers said.

In their earlier work, the team led by Rice graduate student Zhiwei Peng tried many polymers and discovered that a commercial polyimide was the best for the process. For the new work, the lab dissolved boric acid into polyamic acid and condensed it into a boron-infused polyimide sheet, which was then exposed to the laser.

Industrial-scale production

The two-step process produces microsupercapacitors with four times the ability to store an electrical charge and five to 10 times the energy density of the earlier, boron-free version.

The new devices proved highly stable over 12,000 charge-discharge cycles, retaining 90 percent of their capacitance. In stress tests, they handled 8,000 bending cycles with no loss of performance, the researchers reported.

Tour said the technique lends itself to industrial-scale, roll-to-roll production of microsupercapacitors. “What we’ve done shows that huge modulations and enhancements can be made by adding other elements and performing other chemistries within the polymer film prior to exposure to the laser,” he said.

Tour is the T.T. and W.F. Chao Chair in Chemistry as well as a professor of materials science and nanoengineering and of computer science and a member of Rice’s Richard E. Smalley Institute for Nanoscale Science and Technology.

The research is detailed in the journal ACS Nano.

The Air Force Office of Scientific Research and its Multidisciplinary University Research Initiative supported the research.

Abstract of Flexible Boron-Doped Laser Induced Graphene Microsupercapacitors

Heteroatom-doped graphene materials have been intensely studied as active electrodes in energy storage devices. Here, we demonstrate that boron-doped porous graphene can be prepared in ambient air using a facile laser induction process from boric acid containing polyimide sheets. At the same time, active electrodes can be patterned for flexible microsupercapacitors. As a result of boron doping, the highest areal capacitance of as-prepared devices reaches 16.5 mF/cm^2, three times higher than non-doped devices, with concomitant energy density increases of 5 to 10 times at various power densities. The superb cyclability and mechanical flexibility of the device is well-maintained, showing great potential for future microelectronics made from this boron-doped laser induced graphene material.