Scientists see the light on microsupercapacitors: Laser-induced graphene makes simple, powerful energy storage possible

Rice University scientists are making small, flexible microsupercapacitors in a room-temperature process they claim shows promise for manufacturing in bulk. The technique is based on their method to burn patterns of spongy graphene into plastic sheets with a commercial laser. Credit: Tour Group/Rice University

http://phys.org/news/2015-12-scientists-microsupercapacitors.html#jCp

Rice University researchers who pioneered the development of laser-induced graphene have configured their discovery into flexible, solid-state microsupercapacitors that rival the best available for energy storage and delivery.

The devices developed in the lab of Rice chemist James Tour are geared toward electronics and apparel. They are the subject of a new paper in the journal Advanced Materials.

Microsupercapacitors are not batteries, but inch closer to them as the technology improves. Traditional capacitors store energy and release it quickly (as in a camera flash), unlike common lithium-ion batteries that take a long time to charge and release their energy as needed.

Rice's microsupercapacitors 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 devices are manufactured by burning electrode patterns with a commercial laser into plastic sheets in room-temperature air, eliminating the complex fabrication conditions that have limited the widespread application of microsupercapacitors. The researchers see a path toward cost-effective, roll-to-roll manufacturing.

"It's a pain in the neck to build microsupercapacitors 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."

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

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

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

Rice University scientists are making small, flexible microsupercapacitors in a room-temperature process they claim shows promise for manufacturing in bulk. The technique is based on their method to burn patterns of spongy graphene into …more

Tour is convinced the day is coming when supercapacitors replace batteries entirely, as energy storage systems will 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."

 Explore further: Defects are perfect in laser-induced graphene

More information: Lei Li et al. High-Performance Pseudocapacitive Microsupercapacitors from Laser-Induced Graphene, Advanced Materials (2015). DOI: 10.1002/adma.201503333

Read more at: http://phys.org/news/2015-12-scientists-microsupercapacitors.html#jCp

Laser-induced graphene 'super' for electronics

An electron microscope image shows the cross section of laser-induced graphene burned into both sides of a polyimide substrate. The flexible material created at Rice University has the potential for use in electronics or for energy storage. Credit: Tour Group/Rice University

 http://phys.org/news/2015-01-laser-induced-graphene-super-electronics.html#jCp

Rice University scientists advanced their recent development of laser-induced graphene (LIG) by producing and testing stacked, three-dimensional supercapacitors, energy-storage devices that are important for portable, flexible electronics.

The Rice lab of chemist James Tour discovered last year that firing a laser at an inexpensive polymer burned off other elements and left a film of porous graphene, the much-studied atom-thick lattice of carbon. The researchers viewed the porous, conductive material as a perfect electrode forsupercapacitors or electronic circuits.

To prove it, members of the Tour group have since extended their work to make vertically aligned supercapacitors with laser-induced graphene on both sides of a polymer sheet. The sections are then stacked with solid electrolytes in between for a multilayer sandwich with multiple microsupercapacitors.

The flexible stacks show excellent energy-storage capacity and power potential and can be scaled up for commercial applications. LIG can be made in air at ambient temperature, perhaps in industrial quantities through roll-to-roll processes, Tour said.

The research was reported this week in Applied Materials and Interfaces.

Capacitors use an electrostatic charge to store energy they can release quickly, to a camera's flash, for example. Unlike chemical-based rechargeable batteries, capacitors charge fast and release all their energy at once when triggered. But chemical batteries hold far more energy. Supercapacitors combine useful qualities of both - the fast charge/discharge of capacitors and high-energy capacity of batteries - into one package.

LIG supercapacitors appear able to do all that with the added benefits of flexibility and scalability. The flexibility ensures they can easily conform to varied packages - they can be rolled within a cylinder, for instance - without giving up any of the device's performance.

A schematic shows the process developed by Rice University scientists to make vertical microsupercapacitors with laser-induced graphene. The flexible devices show potential for use in wearable and next-generation electronics. Credit: Tour Group/Rice University

"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," Tour said. "We simply stack them up.

"The other key is that we're doing this very simply. Nothing about the process requires a clean room. It's done on a commercial laser system, as found in routine machine shops, in the open air."

Ripples, wrinkles and sub-10-nanometer pores in the surface and atomic-level imperfections give LIG its ability to store a lot of energy. But the graphene retains its ability to move electrons quickly and gives it the quick charge-and-release characteristics of a supercapacitor. In testing, the researchers charged and discharged the devices for thousands of cycles with almost no loss of capacitance.

To show how well their supercapacitors scale up for applications, the researchers wired pairs of each variety of device in serial and parallel. As expected, they found the serial devices delivered double the working voltage, while the parallels doubled the discharge time at the same current density.

The vertical supercapacitors showed almost no change in electrical performance when flexed, even after 8,000 bending cycles.

Tour said that while thin-film lithium ion batteries are able to store more energy, LIG supercapacitors of the same size offer three times the performance in power (the speed at which energy flows). And the LIG devices can easily scale up for increased capacity.

"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," he said.

 Explore further: Defects are perfect in laser-induced graphene

Rice University growing graphene for widespread use

This graphic shows the process of creating bilayer graphene on an insulating substrate, skipping the need to transfer graphene from a metal catalyst. The final image, captured with an electron microscope, clearly shows two layers of graphene produced via the process. (Credit Tour Lab/Rice University)

MY NOTE: ONCE AGAIN, ANOTHER BLOG POST THAT DOESN'T DIRECTLY DISCUSS OR MENTION TERAHERTZ, BUT INVOLVES MORE ADVANCES IN THE DEVELOPMENT OF GRAPHENE, WHICH WILL AFFECT THz, DEVELOPMENT IN THE FUTURE.

http://www.media.rice.edu/media/NewsBot.asp?MODE=VIEW&ID=16162&SnID=832539654

By heating metal to make graphene, Rice University researchers may warm the hearts of high-tech electronics manufacturers.

The lab of Rice chemist James Tour published two papers this month that advance the science of making high-quality, bilayer graphene. They show how to grow it on a functional substrate by first having it diffuse into a layer of nickel.
Graphene is commonly grown on a metal catalyst, usually copper, and must be transferred to an electrically insulating substrate like silicon dioxide before it can be used in a circuit. The transfer process is cumbersome and time-consuming and can be as frustrating as manipulating household plastic wrap, Tour said.
The new processes outlined in two related ACS Nano papers (here and here) show large-scale bilayer graphene can be grown directly onto a variety of insulating substrates. They eliminate the transfer process and facilitate the growth of large sheets of semiconducting graphene ready for incorporation into patterned transistors, Tour said.
“The ability to grow bilayer graphene directly onto an insulator can permit electronic device manufacturers to build transistors without the industrially burdensome step of placing one sheet of graphene upon another," said Tour, Rice's T.T. and W.F. Chao Chair in Chemistry as well as a professor of mechanical engineering and materials science and of computer science.
Graphene, the single-atom-thick form of carbon, has been the subject of much study since its discovery in 2004. Tour's lab has become a major player in graphene research by publishing in recent years papers on unzipping nanotubes into graphene nanoribbons, characterizing its electrical properties through lithography, creating transparent electrodes for touch screens and making graphene from a variety of cheap sources, even Girl Scout cookies. All aim to cut the cost and complexity of making graphene and bring it into widespread use.
A single layer of graphene, which at the atomic scale looks like chicken wire, is a semimetal and has no bandgap; this makes it unsuitable for many electronic applications. But bilayer graphene is a semiconductor. Its properties depend upon the offset or rotation of the layers in relation to each other and it is tunable using an electric field applied across the layers.
The new processes depend on the solubility of carbon atoms in hot nickel. In one study, a group led by graduate student Zhiwei Peng evaporated a coat of nickel onto silicon dioxide and placed a polymer film -- the carbon source -- on top.
Heating the sandwich to 1,000 degrees Celsius in the presence of flowing argon and hydrogen gas allowed the polymer to diffuse into the metal; upon cooling, graphene formed on the nickel and on the silicon dioxide surfaces. When the nickel and incidental graphene that formed on top were etched away, bilayer graphene was left attached to the silicon dioxide substrate.
In the other study, graduate student Zheng Yan shuffled the sandwich. He topped a layer of silicon dioxide with a sliver of one of a variety of polymers and then put the nickel on top. Again, under high temperature and low pressure, bilayer graphene formed between the silicon dioxide and nickel. Experimentation with other substances revealed that bilayer graphene would also form on hexagonal boron nitride, silicon nitride and sapphire.
“This type of process eliminates the need for roll-to-roll transfer of the graphene to an electronic substrate, because bilayer graphene can now be grown directly upon the substrate of interest,” Tour said.
Authors of the first paper, "Growth of Bilayer Graphene on Insulating Substrates," are Yan, Peng, graduate student Zhengzong Sun, former graduate student Jun Yao, postdoctoral research associates Yu Zhu and Zheng Liu, Tour and Pulickel Ajayan, the Benjamin M. and Mary Greenwood Anderson Professor in Mechanical Engineering and Materials Science and of chemistry.
The Office of Naval Research MURI program, Lockheed Martin and the Air Force Office of Scientific Research supported the research.
Authors of the second paper, "Direct Growth of Bilayer Graphene on SiO₂ Substrates by Carbon Diffusion Through Nickel," are Peng, Yan, Sun and Tour.
The Office of Naval Research MURI program, the Air Force Research Laboratory through United Technology Corp., the Air Force Office of Scientific Research and M-I SWACO supported the research.

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ABSTRACTS:
Growth of Bilayer Graphene on Insulating Substrates:
http://pubs.acs.org/doi/abs/10.1021/nn202829y
Direct Growth of Bilayer Graphene on SiO2 Substrates by Carbon Diffusion Through Nickel:
http://pubs.acs.org/doi/abs/10.1021/nn202923y
Download a high-resolution graphic here:
http://www.media.rice.edu/images/media/NEWSRELS/0914_figure.jpg