New Paper-like Material Could Boost Electric Vehicle Batteries

Scanning electron microscope images of
(a) SiO2 nanofibers after drying, (b) SiO2
nanofibers under high magnification (c) silicon
nanofibers after etching, and (d) silicon nanofibers
under high magnification.

Researchers at the University of California, Riverside’s Bourns College of Engineering have developed a novel paper-like material for lithium-ion batteries. It has the potential to boost by several times the specific energy, or amount of energy that can be delivered per unit weight of the battery.

This paper-like material is composed of sponge-like silicon nanofibers more than 100 times thinner than human hair. It could be used in batteries for electric vehicles and personal electronics.

The findings were just published in a paper, “Towards Scalable Binderless Electrodes: Carbon Coated Silicon Nanofiber Paper via Mg Reduction of Electrospun SiO₂ Nanofibers,” in the journal Nature Scientific Reports. The authors were Mihri Ozkan, a professor of electrical and computer engineering, Cengiz S. Ozkan, a professor of mechanical engineering, and six of their graduate students: Zach Favors, Hamed Hosseini Bay, Zafer Mutlu, Kazi Ahmed, Robert Ionescu and Rachel Ye.

The nanofibers were produced using a technique known as electrospinning, whereby 20,000 to 40,000 volts are applied between a rotating drum and a nozzle, which emits a solution composed mainly of tetraethyl orthosilicate (TEOS), a chemical compound frequently used in the semiconductor industry. The nanofibers are then exposed to magnesium vapor to produce the sponge-like silicon fiber structure.

Conventionally produced lithium-ion battery anodes are made using copper foil coated with a mixture of graphite, a conductive additive, and a polymer binder. But, because the performance of graphite has been nearly tapped out, researchers are experimenting with other materials, such as silicon, which has a specific capacity, or electrical charge per unit weight of the battery, nearly 10 times higher than graphite.

(a) Schematic representation of the electrospinning
process and subsequent reduction process. Digital
photographs of (b) as-spun SiO2 nanofibers paper, (c)
etched silicon nanofiber paper, and (d) carbon-coated silicon
nanofiber paper as used in the lithium-ion half-cell
configuration.

The problem with silicon is that is suffers from significant volume expansion, which can quickly degrade the battery. The silicon nanofiber structure created in the Ozkan’s labs circumvents this issue and allows the battery to be cycled hundreds of times without significant degradation.

“Eliminating the need for metal current collectors and inactive polymer binders while switching to an energy dense material such as silicon will significantly boost the range capabilities of electric vehicles,” Favors said.

This technology also solves a problem that has plagued free-standing, or binderless, electrodes for years: scalability. Free-standing materials grown using chemical vapor deposition, such as carbon nanotubes or silicon nanowires, can only be produced in very small quantities (micrograms). However, Favors was able to produce several grams of silicon nanofibers at a time even at the lab scale.

The researchers’ future work involves implementing the silicon nanofibers into a pouch cell format lithium-ion battery, which is a larger scale battery format that can be used in EVs and portable electronics.

The research is supported by Temiz Energy Technologies. The UC Riverside Office of Technology Commercialization has filed patents for inventions reported in the research paper.

http://ucrtoday.ucr.edu/27263

Nano-paper filter can remove viruses

The illustration shows the nanofibers in white and the virus in green. Photograph: Björn Syse

Researchers at the Division of Nanotechnology and Functional Materials, Uppsala University have developed a paper filter, which can remove virus particles with an efficiency matching that of the best industrial virus filters. The paper filter consists of 100 percent high purity cellulose nanofibers, directly derived from nature.

The research was carried out in collaboration with virologists from the Swedish University of Agricultural Sciences/Swedish National Veterinary Institute and is published in the Advanced Healthcare Materials journal.

Virus particles are very peculiar objects- tiny (about thousand times thinner than a human hair) yet mighty. Viruses can only replicate in living cells but once the cells become infected the viruses can turn out to be extremely pathogenic. Viruses can actively cause diseases on their own or even transform healthy cells to malignant tumors.

‘Viral contamination of biotechnological products is a serious challenge for production of therapeutic proteins and vaccines. Because of the small size, virus removal is a non-trivial task, and, therefore, inexpensive and robust virus removal filters are highly demanded’, says Albert Mihranyan, Associate Professor at the Division of Nanotechnology and Functional Materials, Uppsala University, who heads the study.

Cellulose is one of the most common materials to produce various types of filters because it is inexpensive, disposable, inert and non-toxic. It is also mechanically strong, hydrophyllic, stable in a wide range of pH, and can withstand sterilization e.g. by autoclaving. Normal filter paper, used for chemistry, has too large pores to remove viruses.

The undergraduate student Linus Wågberg, Professor Maria Strømme, and Associate Professor Albert Mihranyan at the Division of Nanotechnology and Functional Materials, Uppsala University, in collaboration with virologists Dr. Giorgi Metreveli, Eva Emmoth, and Professor Sándor Belák from the Swedish University of Agricultural Sciences (SLU)/Swedish National Veterinary Institute (SVA), report a design of a paper filter which is capable of removing virus particles with the efficiency matching that of the best industrial virus filters. The reported paper filter, which is manufactured according to the traditional paper making processes, consists of 100 percent high purity cellulose nanofibers directly derived from nature.

The discovery is a result of a decade long research on the properties of high surface area nanocellulose materials, which eventually enabled the scientists to tailor the pore size distribution of their paper precisely in the range desirable for virus filtration.

Previously described virus removal paper filters relied heavily on interception of viruses via electrostatic interactions, which are sensitive to pH and salt concentrations, whereas the virus removal filters made from synthetic polymers and which rely on size-exclusion are produced through tedious multistep phase-inversion processing involving hazardous solvents and rigorous pore annealing processing.

Incidentally, it was the Swedish chemist J.J. Berzelius (1779-1848), one of the most famous alumni of Uppsala University, who was the first one to use the pure wet-laid-all-rag paper for separation of precipitates in chemical analysis. In a way, the virus removal nano-paper filter developed by the Uppsala scientists is the modern day analogue of the widely popular Swedish Filter Paper developed by Berzelius nearly two centuries ago.

Source: http://www.uu.se/en/media/news/article/?id=3317&area=2,10,16&typ=artikel&na=&lang=en#sthash.rKkmbmdN.dpuf

Researchers Grow Carbon Nanofibers Using Ambient Air, Without Toxic Ammonia

Researchers have shown they can grow vertically-aligned carbon nanofibers using ambient air, rather than ammonia gas. Click to enlarge image. (Image free for use. Credit: Anatoli Melechko.)

Researchers from North Carolina State University have demonstrated that vertically aligned carbon nanofibers (VACNFs) can be manufactured using ambient air, making the manufacturing process safer and less expensive. VACNFs hold promise for use in gene-delivery tools, sensors, batteries and other technologies.

Conventional techniques for creating VACNFs rely on the use of ammonia gas, which is toxic. And while ammonia gas is not expensive, it’s not free.

“This discovery makes VACNF manufacture safer and cheaper, because you don’t need to account for the risks and costs associated with ammonia gas,” says Dr. Anatoli Melechko, an adjunct associate professor of materials science and engineering at NC State and senior author of a paper on the work. “This also raises the possibility of growing VACNFs on a much larger scale.”

In the most common method for VACNF manufacture, a substrate coated with nickel nanoparticles is placed in a vacuum chamber and heated to 700 degrees Celsius. The chamber is then filled with ammonia gas and either acetylene or acetone gas, which contain carbon. When a voltage is applied to the substrate and a corresponding anode in the chamber, the gas is ionized. This creates plasma that directs the nanofiber growth. The nickel nanoparticles free carbon atoms, which begin forming VACNFs beneath the nickel catalyst nanoparticles. However, if too much carbon forms on the nanoparticles it can pile up and clog the passage of carbon atoms to the growing nanofibers.

Ammonia’s role in this process is to keep carbon from forming a crust on the nanoparticles, which would prevent the formation of VACNFs.

“We didn’t think we could grow VACNFs without ammonia or a hydrogen gas,” Melechko says. But he tried anyway.

Melechko’s team tried the conventional vacuum technique, using acetone gas. However, they replaced the ammonia gas with ambient air – and it worked. The size, shape and alignment of the VACNFs were consistent with the VACNFs produced using conventional techniques.

“We did this using the vacuum technique without ammonia,” Melechko says. “But it creates the theoretical possibility of growing VACNFs without a vacuum chamber. If that can be done, you would be able to create VACNFs on a much larger scale.”

Melechko also highlights the role of two high school students involved in the work: A. Kodumagulla and V. Varanasi, who are lead authors of the paper. “This discovery would not have happened if not for their approach to the problem, which was free from any preconceptions,” Melechko says. “I think they’re future materials engineers.”

The paper, “Aerosynthesis: Growth of Vertically-aligned Carbon Nanofibres with Air DC Plasma,” is published online inNanomaterials and Nanotechnology. Co-authors include former NC State Ph.D. student Dr. R.C. Pearce; NC State Ph.D. student W.C. Wu; Dr. Joseph Tracy, an associate professor of materials science and engineering at NC State; and D.K. Hensley and T.E. McKnight of Oak Ridge National Laboratory. The work was partially supported by National Science Foundation grant DMR-1056653.

Source: http://news.ncsu.edu/releases/wms-melechko-cnf-ambient-2014/

Less is more with adding graphene to nanofibers

Figuring that if some is good, more must be better, researchers have been trying to pack more graphene, a supermaterial, into structural composites. Collaborative research led by University of Nebraska-Lincoln materials engineers discovered that, in this case, less is more.

The team, led by Yuris Dzenis, McBroom professor of mechanical and materials engineering and a member of UNL's Nebraska Center for Materials and Nanoscience, learned that using a small amount of graphene oxide as a template improves carbon nanomaterials which, in turn, promises to improve composite materials. Composites are used in everything from airplanes to bicycles and golf clubs.

Graphene is a one-atom thick layer of carbon with a crystalline structure that makes it exceptionally strong and an excellent heat and electrical conductor. It was the subject of research that earned the 2010 Nobel Prize in Physics.

UNL engineers collaborated with researchers from Northwestern University and Materials and Electrochemical Research Corp. of Tucson, Ariz., on this study. The UNL team developed a process to incorporate graphene oxide nanoparticles as a template to guide the formation and orientation of continuous carbon nanofibers, which should improve the fiber's properties. That process involves crumpling the graphene, like crumpling a sheet of paper, in a way that improves graphene as a templating and orientation agent. Only small amounts of crumpled graphene nanoparticles are needed. A group led by chemist SonBinh Nguyen of Northwestern synthesized the graphene oxide.

"Many people are trying to put as much graphene as possible into fibers," Dzenis said, adding that it is difficult to do. "But we did the unconventional thing: We used very small quantities followed by carbonization."

The resulting carbon nanofiber structure has an orientation similar to fibers with demonstrated enhanced strength and other properties, Dzenis said. He and his colleagues are now testing their graphene-based nanofibers for these enhanced properties as well as improving the technique.

The method is promising, he said. It could lower the cost of making composites significantly because it requires only small quantities of expensive nanoparticles and uses an inexpensive nanofiber manufacturing process, which was developed at UNL.

"All of this has potential for high-performance but, at the same time, low-cost carbon nanofibers," Dzenis said.

The team reported its findings in the Dec. 10 issue of Advanced Functional Materials. Co-authors are UNL mechanical and materials engineering colleagues Dimitry Papkov and Alexander Goponenko; facilities specialist Xing-Zhong Li of the Nebraska Center for Materials and Nanoscience; Owen C. Compton, Zhi An and SonBinh T. Nguyen of Northwestern; and Alexander Moravsky of Materials and Electrochemical Research Corp.

This research was funded by grants from the U.S. Army Research Office Multidisciplinary University Research Initiative, Air Force Office of Scientific Research and the National Science Foundation.

Source: http://newsroom.unl.edu/releases/2013/12/11/UNL-led+team+finds+less+is+more+with+adding+graphene+to+nanofibers

Nanofibers and Designer Light Traps

Graphic interpretation of higher mode traveling in a tapered
optical fiber. Credit E. Edwards/JQI

Light can be confined inside a reflective medium—a stream of water, a thread of glass fiber. In fiber optics, the light moves, trapped in a glass strand via the mechanism of total internal reflection. 

Light “totally” bounces at the surfaces, back and forth, carrying information over vast distances.

Perhaps the word total should be taken a little loosely, at least at the surface. Here, there is what’s called an evanescent field.

Webster says “evanescent” means “tending to dissipate, like vapor.” In physics, an evanescent wave is a vanishing vibration, occurring at an interface. They occur because nature doesn’t like discontinuity. The evanescent field isn’t the same as leaky, inefficient fibers; it is always present as light moves through the fiber.

“Dissipating, like vapor” doesn’t sound like something useful, but in fact, under certain conditions, evanescent waves can be used to isolate and probe atoms. Atoms trapped in the evanescent wave can interact with light traveling in the fiber. The information from that interaction is not lost; the light then re-enters, or “couples,” back into the fiber and can be captured on a camera.

The fibers in communications are relatively large compared to the wavelength of light, about 10 to 100 times greater depending on the length and use of the fiber. Harnessing evanescent fields requires reducing the fiber core. Here the team heats up a fiber while simultaneously stretching it—a technique reminiscent of glass blowing—down to a diameter of 350 nm. This is more than two times smaller than the light’s wavelength (780 nm), which means that somewhere along the line, the light can’t completely fit inside the fiber. Instead, its electric field is mostly outside the core—where it can interact with atoms, for instance. [see accompanying video of fiber pulling and injected light, monitored on a camera]The cross-section of a light beam, such as those from lasers, often looks smooth, with the brightest part in the middle and decreasing intensity away from the center. But this is only one example of what is called a spatial light “mode.” Higher modes, those that have more spatial components can also be made. These modes visually can look like a doughnut, cloverleaf, or another more complicated pattern.

Higher modes offer some advantages over the lowest order or “fundamental” mode. Due to their complexity, the evanescent field can have comparatively more light intensity in the region of interest –-locally just outside the fiber. These higher order modes can also be used to make different types of optical patterns. Generally speaking, to have complete control over an atomic gas, the researchers require maximal flexibility in the power and shape of the trapping light.

In this experiment, the team squeezes combinations of higher modes of the light into a nanofiber with unprecedented efficiency and purity. Ninety-seven percent passes through the tapered nanofiber—this is compared to previous work of around 20 percent. In contrast to a high purity fundamental mode, their design allows for 99 percent of the light to be in higher mode configurations. This kind of control would potentially translate into more control over evanescent atom traps.

This paper describes some of the first results from the hybrid project at JQI called “Atoms on SQUIDS.” This project seeks to couple cold gases to superconducting systems. Hybrid approaches are collectively seen as a necessity in developing quantum information resources. This particular project is extremely challenging because it requires coupling two platforms that use seemingly disparate technologies.

Check out this video to see the propagation of light in the team’s nanofiber. The experimental results described here took place outside of a vacuum chamber. The team also has a nanofiber under vacuum and has successfully trapped rubidium atoms from a laser-cooled gas.

This article was written by E. Edwards/JQI. Video produced by S. Kelley/E. Edwards/J. Robinson in collaboration with authors. The data/media from paper was re-used with permission of authors.
REFERENCE PUBLICATION
"A low-loss photonic silica nanofiber for higher-order modes," S. Ravets, J.E. Hoffman, L.A. Orozco, S.L. Rolston, G. Beadie, F.K. Fatemi, Optics Express, 21, 18325 (2013)
"Atomic interface between microwave and optical photons," M. Hafezi, Z. Kim, S.L. Rolston, L.A. Orozco, B.L. Lev, J.M. Taylor, Physical Review A, 85, 020302 (2012)




Source: http://jqi.umd.edu/news/nanofibers-and-designer-light-traps

Airbrushing Could Facilitate Large-Scale Manufacture of Carbon Nanofibers

Researchers from North Carolina State University used airbrushing techniques to grow vertically aligned carbon nanofibers on several different metal substrates, opening the door for incorporating these nanofibers into gene delivery devices, sensors, batteries and other technologies.

“Because we’re using an airbrush, this technique could easily be incorporated into large-scale, high-throughput manufacturing processes,” says Dr. Anatoli Melechko, an adjunct associate professor of materials science and engineering at NC State and co-author of a paper describing the work. “In principle, you could cover an entire building with it.”

“It’s common to use nickel nanoparticles as catalysts to grow carbon nanofibers, and we were able to coat metal substrates with nickel nanoparticles using an airbrush,” says Dr. Joseph Tracy, an associate professor of materials science and engineering at NC State and senior author of the paper. “Airbrushing gives us a fairly uniform coating of the substrate and it can be applied to a large area at room temperature in a short period of time.”

After applying the nickel nanoparticles, the researchers airbrushed the substrate with a layer of silicon powder and heated the coated substrate to 600 degrees Celsius in a reactor filled with acetylene and ammonia gas. In the reactor, carbon nanofibers formed under the nickel nanoparticles and were held upright by a silicon-enriched coating. The finished product resembles a forest of nanofibers running perpendicular to the substrate. The researchers tested this technique successfully on aluminum, copper and titanium substrates.

“Growing carbon nanofibers on a metal substrate means the interface between the two materials is highly conductive, which makes the product more useful as an electrode material for use in a range of potential applications,” says Mehmet Sarac, a Ph.D. student at NC State and lead author of the paper.

The paper, “Airbrushed Nickel Nanoparticles for Large-Area Growth of Vertically Aligned Carbon Nanofibers on Metal (Al, Cu, Ti) Surfaces,” was published online Sept. 9 in ACS Applied Materials & Interfaces. The paper was co-authored by NC State Ph.D. students Bryan Anderson, and Adedapo Oni; former NC State graduate students Dr. Ryan Pearce and Justin Railsback; former NC State postdoctoral researcher Dr. Ryan White; Dr. James LeBeau, an assistant professor of materials science and engineering at NC State; and Dale Hensley of Oak Ridge National Laboratory. The work was supported by the National Science Foundation, the Defense Threat Reduction Agency, the U.S. Department of Energy and the Republic of Turkey’s Ministry of National Education.

Source http://news.ncsu.edu/releases/wms-tracy-airbrush-2013/