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April 16th, 2013

Other materials stories that may be of interest

Published on April 16th, 2013 | By: Eileen De Guire

Roll-to-roll coating of electrodes at Fraunhofer IWS: The scientists now have optimized the design of anode and cathode for lithium-sulfur batteries. Credit: Jürgen Leibmann.

A longer life for lithium-sulfur batteries

There are currently over 40 million cars on Germany’s roads. Only a fraction of them are powered by electric energy—around 6,400 vehicles. The comparatively short range of electric cars doesn’t help their popularity. An extremely promising avenue of research is the lithium-sulfur battery, which is significantly more powerful and less expensive than the better-known lithium-ion battery. Although their short lifespan has made them unsuitable for use in cars before now, this may be about to change in the foreseeable future. Scientists at the Fraunhofer Institute for Material and Beam Technology IWS in Dresden have developed a new design that increases the charge cycles of lithium-sulfur batteries by a factor of seven. “During previous tests, the batteries scarcely crossed the 200-cycle mark. By means of a special combination of anode and cathode material, we have now managed to extend the lifespan of lithium-sulfur button cells to 1,400 cycles,” says Holger Althues, head of the Chemical Surface Technology group at IWS, who is delighted with his team’s breakthrough. The anode of the team’s prototype is not made from the usual metallic lithium, but from a silicon-carbon compound instead. This compound is significantly more stable, as it changes less during each charging process than metallic lithium. The more the structure of the anode changes, the more it interacts with the liquid electrolyte, which is situated between the anode and the cathode and carries the lithium-ions.

ORNL leading study focused on afterlife of electric vehicle batteries

Once they’ve finished powering electric vehicles for hundreds of thousands of miles, it may not be the end of the road for automotive batteries, which researchers believe can provide continued benefits for consumers, automakers and the environment. Five used Chevrolet Volt batteries are at the heart of the Department of Energy Oak Ridge National Laboratory’s effort to determine the feasibility of a community energy storage system that would put electricity onto the grid. Over the next year, researchers from ORNL, General Motors and the ABB Group will conduct studies and compile data using a first-of-its-kind test platform officially commissioned today. “With about one million lithium-ion batteries per year coming available from various automakers for the secondary market beginning in 2020, we see vast potential to supplement power for homes and businesses,” said Imre Gyuk, manager of the Energy Storage Research Program in DOE’s Office of Electricity Delivery and Energy Reliability. “Since these batteries could still have up to 80 percent of their capacity, they present a great opportunity for use in stationary storage devices before sending them to be recycled.”

Sensor for asteroid camera passes critical test

Scientists are testing a new sensor designed to be the eyes of a future asteroid-tracking mission. “The Near Earth Object Camera (NEOCam) sensor will increase our ability to detect hazardous asteroids near the Earth and improve our understanding of threatening objects,” says William J. Forrest, professor of astronomy at the University of Rochester. Once launched, the space-based telescope would be positioned at a location about four times the distance between Earth and the moon. From this lofty perch, NEOCam could observe the comings and goings of objects near Earth without the impediments to efficient observing like cloud cover and even daylight. Asteroids do not emit visible light, they reflect it, which can make it difficult to determine size using visible light telescopes. But asteroids always emit infrared radiation. Asteroids emit most of their radiation at infrared wavelengths near about 10 microns (0.0004 inches), which humans perceive as heat. There is also relatively less radiation from stars and galaxies at these wavelengths, which simplifies detection of faint moving objects. “This sensor works at higher temperatures than any other similar ones we have at the moment,” says Judith Pipher, emeritus professor in physics and astronomy at Rochester. “This means they can be passively cooled, making the instrument less heavy and less expensive to put into space.”

First Demonstration of the Storage And Release of Light in a Metamaterial

(MIT Technology Review) The ability to slow down and trap light has become a hot topic in physics since it was first observed in the 1990s. The ability to trap electromagnetic waves has important applications in areas such as information storage, sensing and quantum optics. But the field has not progressed quite as quickly as many had hoped. That’s largely because of the complexity of the experimental setup and the difficulty in releasing the waves with their original properties after they have been trapped. Recently, Toshihiro Nakanishi and pals at Kyoto University in Japan reveal a new approach to this problem that has the potential to bring the routine storage and release of electromagnetic waves closer to reality. Conventional light trapping relies on atoms such as cesium and rubidium that have special combinations of ground and excited states. These atoms absorb at one specific frequency. However by zapping them with a laser at another frequency, called a probe, that excites the atoms, light can then pass through. This phenomenon is called electromagnetically induced transparency. But there is another way to achieve this kind of trapping, say Nakanishi and co. Instead of a cloud of atoms, these guys have created a metamaterial but does the same job. In this case, Nakanishi and company have created a metamaterial in which each repeating unit contains two variable capacitors. One of the capacitors is designed to absorb and radiate waves at a particular frequency while the other is designed to trap them. If the capacitors are tuned to the same frequency, any light at that frequency is absorbed and trapped. Detuning the capacitors then releases the electromagnetic waves, allowing them to continue on their way.

Ultrasound signal reveals microstructure

(American Physical Society) As a steel girder or concrete slab ages, its internal microstructure may change and lead to catastrophic failure. A proposed technique for analyzing the noise in ultrasound signals, described in Physical Review E, could provide an early warning system. The method is an adaption of an analysis previously used to characterize DNA. In the new computer simulations, the technique was able to correctly identify a wide range of microstructures in a one-dimensional material. The flooding of a river or a stock market crash may seem unpredictable, but often these events have some hidden relation to the past. The level of the river may be more likely to go up if it went up the week before, for example. It’s as if these systems retain some memory of past fluctuations, rather than having totally independent fluctuations from one moment to the next. One of the mathematical techniques for identifying such long-term memory in seemingly random data is called detrended fluctuation analysis (DFA). It has been used in the study of long-range correlations in DNA sequences, heart rates, human stride lengths, and temperature records. DFA could also be useful in ultrasonic evaluation of materials. Engineers currently use the scattering of ultrasound signals in a material as a way to nondestructively test for cracks or other large-scale features. However, research in 2004 showed that DFA performed on ultrasound signals from a cast-iron sample could reveal the fractal nature of the microstructure. André Vieira of University of São Paulo in Brazil and his colleagues at the Federal University of Ceará in Brazil have now developed a more general DFA framework for ultrasound inspection.

Layered 2D nanocrystals promising new semiconductor

(R&D) Researchers are developing a new type of semiconductor technology for future computers and electronics based on “2D nanocrystals” layered in sheets less than a nanometer thick that could replace today’s transistors. The layered structure is made of a material called molybdenum disulfide, which belongs to a new class of semiconductors—metal di-chalogenides—emerging as potential candidates to replace today’s technology, complementary metal oxide semiconductors, or CMOS. New technologies will be needed to allow the semiconductor industry to continue advances in computer performance driven by the ability to create ever-smaller transistors. It is becoming increasingly difficult, however, to continue shrinking electronic devices made of conventional silicon-based semiconductors. “We are going to reach the fundamental limits of silicon-based CMOS technology very soon, and that means novel materials must be found in order to continue scaling,” says Saptarshi Das, who has completed a doctoral degree, working with Joerg Appenzeller, a professor of electrical and computer engineering and scientific director of nanoelectronics at Purdue’s Birck Nanotechnology Center. “I don’t think silicon can be replaced by a single material, but probably different materials will co-exist in a hybrid technology.” Findings show that the material performs best when formed into sheets of about 15 layers with a total thickness of 8 to 12 nanometers. The researchers also have developed a model to explain these experimental observations. “Our model is generic and, therefore, is believed to be applicable to any 2D layered system,” Das says. Molybdenum disulfide is promising in part because it possesses a bandgap, a trait that is needed to switch on and off, which is critical for digital transistors to store information in binary code.

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