A new type of composite material with peapod structures can help improve performance of lithium-ion batteries

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Lithium-ion batteries are used to power a wide range of electronic devices, including computers, cameras, digital audio players and calculators. Tremendous effort has been devoted to the development of lithium-ion batteries, especially in improving the efficiency and integrity of the battery electrodes. This is because during the discharging and charging processes, lithium ions are repeatedly incorporated into and extracted from the electrodes by alloy formation or chemical conversion. These recurring events are known to cause the progressive degradation of the electrodes, irreversibly damaging battery performance.

Yu Wang at the A*STAR Institute of Chemical and Engineering Sciences and co-workers have now demonstrated an elegant strategy to reduce the degradation problem and increase the capacity retention of lithium-ion batteries over many charge–discharge cycles. The strategy involves the use of acomposite materialwith a peapod structure comprising cobalt oxide (Co₃O₄) nanoparticles embedded in carbon fibers (see image).

Cobalt oxide is a promising material for anodes in lithium-ion batteries because its capacity for holding ions is higher than that of conventional electrode materials, such as tin. In addition, Co₃O₄can be easily converted to LiCoO₂, which is the material currently used in commercial cathodes. The researchers made the peapod structures by heating cobalt carbonate hydroxide nanobelts coated with layers of polymerized glucose in an inert atmosphere at 700ºC and then in air at 250ºC. Electrodes built using the peapod composite had enhancedlithiumstorage and capacity retention—delivering 91% of the total possible capacity after 50 charge–discharge cycles.

“The Co₃O₄nanoparticles act as active materials to store lithium ions and the hollow carbon fibers protect and prevent the Co3O4 nanoparticles from aggregating and collapsing,” says Wang. Thecarbon fibersalso play the role of conducting electrons from the nanoparticles.

According to Wang, aside from the promising application in lithium-ion batteries, the fabrication of the peapod composite is an achievement in itself, as it is the first time that such isolated magnetic nanoparticles embedded in hollow fibers have been produced. Scanning electron microscopy revealed that the peapod composite exhibits a uniform morphology, with pod lengths of up to several micrometers and pod diameters of as small as 50 nanometers. The researchers believe that their method could be extended to generate encapsulated nanoparticles using a wide range of materials with applications beyond lithium-ion batteries, for example, in gene engineering, catalysis, gas sensing and the manufacture of capacitors and magnets.

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A dash of disorder yields a very efficient photocatalyst

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(PhysOrg.com) -- A little disorder goes a long way, especially when it comes to harnessing the sun’s energy. Scientists from the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) jumbled the atomic structure of the surface layer of titanium dioxide nanocrystals, creating a catalyst that is both long lasting and more efficient than all other materials in using the sun’s energy to extract hydrogen from water.

Their photocatalyst, which accelerates light-driven chemical reactions, is the first to combine durability and record-breaking efficiency, making it a contender for use in several clean-energy technologies.

It could offer a pollution-free way to producehydrogenfor use as an energy carrier in fuel cells. Fuel cells have been eyed as an alternative to combustion engines in vehicles. Molecular hydrogen, however, exists naturally on Earth only in very low concentrations. It must be extracted from feedstocks such as natural gas or water, an energy-intensive process that is one of the barriers to the widespread implementation of the technology.

“We are trying to find better ways to generate hydrogen from water using sunshine,” says Samuel Mao, a scientist in Berkeley Lab’s Environmental Energy Technologies Division who led the research.“In this work, we introduced disorder in titanium dioxide nanocrystals, which greatly improves its light absorption ability and efficiency in producing hydrogen from water.”

Mao is the corresponding author of a paper on this research that was published online Jan. 20, 2011 inScience Expresswith the title“Increasing Solar Absorption for Photocatalysis with Black, Hydrogenated Titanium Dioxide Nanocrystals.” Co-authoring the paper with Mao are fellow Berkeley Lab researchers Xiaobo Chen, Lei Liu, and Peter Yu.

Mao and his research group started with nanocrystals of titanium dioxide, which is a semiconductor material that is used as a photocatalyst to accelerate chemical reactions, such as harnessing energy from the sun to supply electrons that split water into oxygen and hydrogen. Although durable, titanium dioxide isn’t a very efficient photocatlayst. Scientists have worked to increase its efficiency by adding impurities and making other modifications.

The Berkeley Lab scientists tried a new approach. In addition to adding impurities, they engineered disorder into the ordinarily perfect atom-by-atom lattice structure of the surface layer of titanium dioxide nanocrystals. This disorder was introduced via hydrogenation.

The result is the first disorder-engineered nanocrystal. One transformation was obvious: the usually white titanium dioxide nanocrystals turned black, a sign that engineered disorder yielded infrared absorption.

The scientists also surmised disorder boosted the photocatalyst’s performance. To find out if their hunch was correct, they immersed disorder-engineered nanocrystals in water and exposed them to simulated sunlight. They found that 24 percent of the sunlight absorbed by the photocatalyst was converted into hydrogen, a production rate that is about 100 times greater than the yields of most semiconductor photocatalysts.

In addition, their photocatalyst did not show any signs of degradation during a 22-day testing period, meaning it is potentially durable enough for real-world use.

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Berkeley Lab scientist Samuel Mao leads a research team that is searching for sustainable ways to generate hydrogen for use in clean-energy technologies. In a first-of-its-kind development, they jumbled the surface layer of titanium dioxide nanocrystals, a feat that turned the material from white to black. It also created a photocatalyst whose efficiency outpaces others in using the sun’s energy to extract hydrogen from water. (Photo by Roy Kaltschmidt, Berkeley Lab Public Affairs)

Its landmark efficiency stems largely from the photocatalyst’s ability to absorb infrared light, making it the first titanium dioxide photocatalyst to absorb light in this wavelength. It also absorbs visible and ultraviolet light. In contrast, most titanium dioxide photocatalysts only absorbs ultraviolet light, and those containing defects may absorb visible light. Ultraviolet light accounts for less than ten percent of solar energy.

“The more energy from the sun that can be absorbed by aphotocatalyst, the more electrons can be supplied to a chemical reaction, which makes blacktitanium dioxidea very attractive material,” says Mao, who is also an adjunct engineering professor in the University of California at Berkeley.

The team’s intriguing experimental findings were further elucidated by theoretical physicists Peter Yu and Lei Liu, who explored how jumbling the latticework of atoms on the nanocrystal’s surface via hydrogenation changes its electronic properties. Their calculations revealed that disorder, in the form of lattice defects and hydrogen, makes it possible for incoming photons to excite electrons, which then jump across a gap where no electron states can exist. Once across this gap, the electrons are free to energize the chemical reaction that splits water into hydrogen and oxygen.

“By introducing a specific kind of disorder, mid-gap electronic states are created accompanied by a reduced band gap,” says Yu, who is also a professor in the University of California at Berkeley’s Physics Department.“This makes it possible for the infrared part of the solar spectrum to be absorbed and contribute to the photocatalysis.”

This research was supported by the Department of Energy’s Office of Energy Efficiency and Renewable Energy. Transmission electron microscopy imaging used to study the nanocrystals at the atomic scale was performed at the National Center for Electron Microscopy, a national user facility located at Berkeley Lab.

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Touchscreens made of carbon

Touchscreens are in -- although the technology still has its price. The little screens contain rare and expensive elements. This is the reason why researchers at Fraunhofer are coming up with an alternative display made of low-priced renewable raw materials available all over the world. The researchers are presenting touchscreens that contain carbon nanotubes at the nano tech 2011 fair in Tokyo from Feb. 16-18.

Just touching it slightly with the tips of your fingers is enough. You can effortlessly write, navigate, open menu windows or rotate images on touchscreens. Within fractions of a second your touch is translated into control commands that a computer understands. At first glance, this technology borders on the miraculous, but in real life this mystery just is a wafer-thin electrode under theglass surfaceof the display made of indium-tin-oxide, ITO. This material is nothing short of ideal for use in touchscreens because it is excellent at conducting slight currents and lets the colors of the display pass through unhindered. But, there is a little problem: there are very few deposits of indium anywhere in the world. In the long term, the manufacturers of electronic gadgets are afraid that they will be dependent upon the prices set by suppliers. This is the reason why indium is one of what people call"strategic metals."

Therefore, private industry is very interested in alternatives to ITO that are similarly efficient. The researchers at Fraunhofer have succeeded at coming up with a new material forelectrodesthat is on the same level as ITO and on top of it is much cheaper. Its main components arecarbonnanotubes and low-cost polymers. This new electrode foil is composed of two layers. One is the carrier, a thin foil made of inexpensive polyethylenterephthalate PET used for making plastic bottles. Then a mixture of carbon-nanotubes and electrically conducting polymers is added that is applied to the PET as a solution and forms a thin film when it dries.

In comparison to ITO, these combinations of plastics have not been particularly durable because humidity, pressure or UV light put a strain on the polymers. The layers became brittle and broke down. Only carbon nanotubes have made them stable. The carbon nanotubes harden on the PET to create a network where the electrically conducting polymers can be firmly anchored. That means that this layer is durable in the long run. Ivica Kolaric, project manager from Fraunhofer Institute for Manufacturing Engineering and Automation IPA, concedes that"the electrical resistance of our layer is somewhat greater than that of the ITO, but it's easily enough for an application in electrical systems."Its merits are unbeatable: carbon is not only low-cost and available all over the world. It is also a renewable resource that you can get from organic matter such as wood. Kolaric and his colleagues will be presenting their carbon touchdisplay at the 2011 nano tech fair. Since 2003 Fraunhofer researchers show their developments at the annual trade show.

There are a whole series of implementations for the new technology. This foil is flexible and can be used in a variety of ways. Kolaric sums up by saying"we could even make photovoltaic foils out of it to line corrugated roofs or other uneven structures."The researcher has already set up pilot production where the foil can be enhanced for a wide range of applications.

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Butterfly wings behind anti-counterfeiting technology

(PhysOrg.com) -- Imagine a hole so small that air can't go through it, or a hole so small it can trap a single wavelength of light. Nanotech Security Corp., with the help of Simon Fraser University researchers, is using this type of nano-technology– 1,500 times thinner than a human hair and first of its kind in the world– to create unique anti-counterfeiting security features.

The technology is first being applied to banknotes but it also has many more practical applications, such as authenticating legal documents, retail merchandise, concert tickets, stock certificates, visas, passports, and pharmaceuticals.

SFU applied sciences grad Clint Landrock started the initial research into nanoholes under the guidance of SFU engineering science professor Bozena Kaminska. When the pair pitched their idea to Doug Blakeway, SFU Venture Connection’s entrepreneur in residence and also CEO and chairman of Nanotech, he was immediately intrigued by the technology’s potential.

“I love nanotechnology but I really have not seen a commercialization of it that can make you money in the near term,” said Blakeway.“When this was initially presented to me by Bozena and Clint, I immediately saw their vision and they were only after one application– creating anti-counterfeiting features for banknotes. I felt this could be the first commercial application of nanotechnology in the world. I kept thinking of applications for it and how it could be used; the technologies and potential astound me.”

Landrock and Kaminska both continue their work as part of Nanotech’s scientific team. The company’s Nano-Optic Technology for Enhanced Security (NOtES) product stems from an idea originating in the purest form of nature– insects using colorful markings to identify themselves.

How this works is microscopic gratings composed of nanostructures interact withlightto produce the shimmering iridescence seen on the Costa Rican morpho butterfly. The nanostructures act to reflect and refract light waves to produce the morpho’s signature blue wings and absorb other unwanted light.

The highly advanced wing structures are the result of many millennia of evolution, and only recently have Nanotech's scientists discovered how to reproduce these structures reliably. While others have talked about the possibility of re-creating it, Nanotech has made this a reality.

The U.S. Treasury, which produces up to 11 billion banknotes annually, is a potential customer for Nanotech’s product. The new U.S. $100 bill, designed with state-of-the art security features, was supposed to be introduced in February 2011 but it’s been delayed due to some manufacturing issues.

Banknotes contain several security features– some that you can plainly see and some that only machines can read– such as hologram strips, security threads woven into the paper, watermarks, color-shifting inks, raised type, and UV inks.

According to Blakeway, Nanotech’s product– which has attracted the attention of treasuries internationally– is superior to holograms and can’t be duplicated.

“Nobody has ever done this,” he said.“We have succeeded while everybody is still trying to duplicate or imitate a butterfly’s wing because it absorbs light and gives off the color. There’s no color pigment– there’s nothing like a dye or anything else. It’s a hole that traps light and releases color.

“You can’t copy or scan it in, you can’t inkjet it on paper, you can’t do any of these things. It’s extremely sophisticated and expensive to make the shims and dyes to produce, but very inexpensive to produce it at the end. Anywhere you can think of where a hologram is being used today, our technology can replace it. It’s more secure than a hologram. You can’t lift it off– we can put it onto metal, plastic, or paper.”

SFU Venture Connections offers training and support programs for SFU entrepreneurs. It links students, faculty and local entrepreneurs with experienced advisors and funding opportunities.

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Researchers develop unique combination of elements for thermal nanotape

Semiconductor Research Corporation (SRC) and researchers from Stanford University have developed a novel combination of elements that yields a unique nanostructure material for packaging. This advance should allow longer life for semiconductor devices while costing less than current state-of-the-art materials. In addition to chip manufacturers, several other industries could also gain greater product efficiencies from related thermal energy management technology.

Forsemiconductors, the improvement will come in the form of packaging for devices. Presently, manufacturers must rely on tiny pins or thick solder to bond sections of the semiconductor in order for the device to perform. However, current solder materials tend to degrade and fail due to heat andmechanical stress. In order to continue the scaling ofintegrated circuits, SRC and Stanford have researched materials that provide a high thermal connectivity— comparable to copper— with the flexible compliance of foam. The answer has been created through a nanostructured thermal tape that conducts heat like a metal while allowing the neighboring materials to expand and contract with temperature changes (metals are too stiff to allow this). This ability to reduce chip temperatures while remaining compliant is a key breakthrough for electronic packaging.

“A big roadblock to increasing the performance of modern chips is hot spots, or millimeter-sized regions of high power generation. This advance in nanostructured materials and methods will allow us to better cool these spots and serves as a key enabler for densification of computational circuitry,” said Professor Ken Goodson, lead researcher for SRC at Stanford University.“This can help packaging to withstand the demands of Moore’s Law.”

In addressing the challenges of miniaturization, the first line of defense for hot spots is the interface material. Incorporating nearly two decades of advanced research and simulations for problems at the packaging level— much of it funded by SRC— the Stanford team ultimately arrived at their unique combination of binder materials surrounding carbon nanotubes. This innovation is expected to facilitate the highest thermal conduction and the most desirable level of elasticity of any known packaging solutions.

“Researchers love to create useful materials and structures that we’ve never seen before, and this new thermal nanotape revolutionizes the chip’s heat sink contact,” said Jon Candelaria, director of Interconnect and Packaging Sciences at SRC.“Instead of being forced to rely upon the properties of just a single material, this combination gives the integrated circuits industry an opportunity to circumvent severe performance limitations and continue to improvepackagingwithout adding cost.”

While the research was funded by members of SRC to enhance computer chips, demand for applications of this kind of thermal interface also is rising in other industries. For instance, several automotive-related companies hope to recover electrical power from hot exhaust gases in cars and trucks using thermoelectric energy converters— enabling better fuel economy— but reliable interfaces are a problem for this technology. Professor Goodson leads a major grant from the National Science Foundation-Department of Energy Partnership on Thermoelectric Devices for Vehicle Applications, with the goal of transferring the SRC-funded interface work to vehicles.

Patents for the technology are pending. The next step in the research is to license the new methods and materials to advanced thermal-interface companies for perfection of the application. End users are expected to benefit from the technology by 2014.

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High-performance capacitor could lead to better rechargeable batteries

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(PhysOrg.com) -- In order to develop next-generation electric vehicles, solar energy systems, and other clean energy technologies, researchers need an efficient way to store the energy. One of the key energy storage devices for these applications and others is a supercapacitor, also called an electric double-layer capacitor. In a recent study, scientists have investigated the possibility of using a material called zeolite-templated carbon for the electrode in this type of capacitor, and found that the material’s unique pore structure greatly improves the capacitor's overall performance.

The researchers, Hiroyuki Itoi, Hirotomo Nishihara, Taichi Kogure, and Takashi Kyotani, from Tohoku University in Sendai, Japan, have published their results on the high-performance electric double-layer capacitor in a recent issue of theJournal of the American Chemical Society.

To store energy, the electric double-layer capacitor is charged by ions that migrate from a bulk solution to an electrode, where they are adsorbed. Before reaching the electrode’s surface, the ions have to travel through narrow nanopores as quickly and efficiently as possible. Basically, the quicker the ions can travel down these paths, the quicker the capacitor can be charged, resulting in a high rate performance. Also, the greater the adsorbed ion density in the electrode, the greater the charge that the capacitor can store, resulting in a high volumetric capacitance.

Recently, scientists have been testing materials with pores of various sizes and structures to try to achieve both quick ion transport and high adsorption ion density. But the two requirements are somewhat contradictory, since ions can travel more quickly through larger nanopores, but large nanopores make the electrode density low and thus decrease the adsorbed ion density.

“In this work, we have successfully demonstrated that it is possible to meet the two seemingly contradictory requirements, high power density and high volumetric capacitance, with zeolite-templated carbon,” Nishihara toldPhysOrg.com.

The zeolite-templated carbon consists of nanopores that are 1.2 nm in diameter (smaller than most electrode materials) and that have a very ordered structure (whereas other pores can be disordered and random). The nanopores’ small size makes the adsorbed ion density high, while the ordered structure– described as a diamond-like framework– allows the ions to quickly pass through the nanopores. In a previous study, the researchers showed that zeolite-templated carbon with nanopores smaller than 1.2 nm cannot enable fast ion transport, suggesting that this size may provide the optimal balance between high rate performance and high volumetric capacitance.

In tests, the zeolite-templated carbon’s properties exceeded those of other materials, demonstrating its potential to be used as an electrode for high-performance electric double-layer capacitors.

“We are now trying to further increase the energy density of the zeolite-templated carbon up to the same level of secondary batteries,” Nishihara said.“If such an electric double layercapacitoris developed and used for mobile devices, such as cellular phones, their charging time can be shortened to only a few minutes. Another important future application of electric double layer capacitors is a support of secondary batteries inelectric vehiclesto prolong the battery's lifetime. Also for this purpose, achieving a higherenergydensity is one of the key issues.”

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Atom-thick sheets unlock future technologies

(PhysOrg.com) -- A new way of splitting layered materials, similar to graphite, into sheets of material just one atom thick could lead to revolutionary new electronic and energy storage technologies.

An international team, led by Oxford University and Trinity College Dublin scientists, has invented a versatile method for creating these one-atom thick 'nanosheets' from a range of materials using mild ultrasonic pulses, like those generated by jewellery cleaning devices, and common solvents. The new method is simple, fast, and inexpensive, and could be scaled up to work on an industrial scale.

The team publish a report of the research in this week'sScience.

Each one-millimetre-thick layer of graphite is made up of around three million layers of graphene– a flat sheet of carbon one atom thick– stacked one on top of the other.

'Because of its extraordinary electronic properties graphene has been getting all the attention, including a recent Nobel Prize, as physicists hope that it might, one day, compete with silicon in electronics,' said Dr Valeria Nicolosi of Oxford University’s Department of Materials, who led the research with Professor Jonathan Coleman of Trinity College Dublin. 'But in fact there are hundreds of other layered materials that could enable us to create powerful new technologies.'

Professor Coleman, of Trinity College Dublin, said: 'These novel materials have chemical and electronic properties which are well suited for applications in new electronic devices, super-strong composite materials and energy generation and storage. In particular, this research represents a major breakthrough towards the development of efficient thermoelectric materials.'

There are over 150 of these exotic layered materials– such as Boron Nitride, Molybdenum disulfide, and Tungsten disulfide– that have the potential to be metallic, semi-metallic or semiconducting depending on their chemical composition and how their atoms are arranged.

For decades researchers have tried to create nanosheets of these kind of materials as arranging them in atom-thick layers would enable us to unlock their unusual electronic and thermoelectric properties. However, all previous methods were extremely time consuming and laborious and the resulting materials were fragile and unsuited to most applications.

'Our new method offers low-costs, a very high yield and a very large throughput: within a couple of hours, and with just 1 mg of material, billions and billions of one-atom-thick graphene-like nanosheets can be made at the same time from a wide variety of exotic layered materials,' said Dr Nicolosi.

Nanosheets created using this method can be sprayed onto the surface of other materials, such as silicon, to produce‘hybrid films’ which, potentially, enable their exotic abilities to be integrated with conventional technologies. Such films could be used to construct, among other things, new designs of computing devices, sensors or batteries.

A report of the research, 'Two-dimensional nanosheets produced by liquid exfoliation of layered materials', is published in the 4 February edition of the journalScience.

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