Rice University

Rice University (4)

Here's a reason to be glad about madder: The climbing plant has the potential to make a greener rechargeable battery.

Scientists at Rice University and the City College of New York have discovered that the madder plant, aka Rubia tinctorum, is a good source of purpurin, an organic dye that can be turned into a highly effective, natural cathode for lithium-ion batteries. The plant has been used since ancient times to create dye for fabrics.  

The discovery is the subject of a paper that appears today in Nature's online, open-access journal Scientific Reports.

The goal, according to lead author Arava Leela Mohana Reddy, a research scientist in the Rice lab of materials scientist Pulickel Ajayan, is to create environmentally friendly batteries that solve many of the problems with lithium-ion batteries in use today.

"Green batteries are the need of the hour, yet this topic hasn’t really been addressed properly," Reddy said. "This is an area that needs immediate attention and sustained thrust, but you cannot discover sustainable technology overnight. The current focus of the research community is still on conventional batteries, meeting challenges like improving capacity. While those issues are important, so are issues like sustainability and recyclability."

While lithium-ion batteries have become standard in conventional electronics since their commercial introduction in 1991, the rechargeable units remain costly to manufacture, Reddy said. "They're not environmentally friendly. They use cathodes of lithium cobalt oxide, which are very expensive. You have to mine the cobalt metal and manufacture the cathodes in a high-temperature environment. There are a lot of costs.

"And then, recycling is a big issue," he said. "In 2010, almost 10 billion lithium-ion batteries had to be recycled, which uses a lot of energy. Extracting cobalt from the batteries is an expensive process."

Reddy and his colleagues came across purpurin while testing a number of organic molecules for their ability to electrochemically interact with lithium and found purpurin most amenable to binding lithium ions. With the addition of 20 percent carbon to add conductivity, the team built a half-battery cell with a capacity of 90 milliamp hours per gram after 50 charge/discharge cycles. The cathodes can be made at room temperature, he said.

"It's a new mechanism we are proposing with this paper, and the chemistry is really simple," Reddy said. He suggested agricultural waste may be a source of purpurin, as may other suitable molecules, which makes the process even more economical.

Innovation in the battery space is needed to satisfy future demands and counter environmental issues like waste management, "and hence we are quite fascinated by the ability to develop alternative electrode technologies to replace conventional inorganic materials in lithium-ion batteries," said Ajayan, Rice's Benjamin M. and Mary Greenwood Anderson Professor in Mechanical Engineering and Materials Science and of chemistry.

“We're interested in developing value-added chemicals, products and materials from renewable feedstocks as a sustainable technology platform,” said co-lead author George John, a professor of chemistry at the City College of New York-CUNY and an expert on bio-based materials and green chemistry. "The point has been to understand the chemistry between lithium ions and the organic molecules. Now that we have that proper understanding, we can tap other molecules and improve capacity."

Recent work by the Ajayan Group combines silicon and a porous nickel current collector in a way that has proven effective as a high-capacity anode, the other electrode in a lithium-ion battery. That research was reported recently in the American Chemical Society journal Nano Letters.

But Reddy hopes to formulate completely green batteries. The team is looking for organic molecules suitable for anodes and for an electrolyte that doesn't break the molecules down. He fully expects to have a working prototype of a complete organic battery within a few years. "What we've come up with should lead to much more discussion in the scientific community about green batteries," he said.

Co-authors of the paper are visiting scholar Porramate Chumyim and former graduate student Sanketh Gowda of Rice; postdoctoral researcher Subbiah Nagarajan, facilities manager Padmanava Pradhan and graduate student Swapnil Jadhav of the City College of New York; and Madan Dubey of the U.S. Army Research Laboratory.

The research was funded by the Army Research Office.

For more information, visit: www.nature.com/srep/2012/121211/srep00960/full/srep00960.html

Tuesday, 30 October 2012 11:10

Microbullets Reveal Material Strengths

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In the macro world, it's easy to see what happens when a bullet hits an object. But what happens at the nanoscale with very tiny bullets?

A Rice University lab, in collaboration with researchers at the Massachusetts Institute of Technology and its Institute for Soldier Nanotechnologies, decided to find out by creating the nanoscale target materials, the microscale ammo and even the method for firing them.

In the process, they gathered a surprising amount of information about how materials called block copolymers dissipate the strain of sudden impact.

The goal of researchers is to find novel ways to make materials more impervious to deformation or failure for stronger and lighter body armor, jet engine turbine blades for aircraft, and for cladding to protect spacecraft and satellites from micrometeorites and space junk. Their work was detailed in the online journal Nature Communications.

The group was led by Rice materials scientist Ned Thomas, the William and Stephanie Sick Dean of Rice's George R. Brown School of Engineering, and Rice research scientist and lead author Jae-Hwang Lee.

The researchers were inspired by their observations in macroscopic ballistic tests in which a complex multiblock copolymer polyurethane material showed the ability to not only stop a 9 mm bullet but also seal the entryway behind it.

"The polymer has actually arrested the bullet and sealed it," Thomas said, holding a hockey puck-sized piece of clear plastic with three bullets firmly embedded. "There's no macroscopic damage; the material hasn't failed; it hasn't cracked. You can still see through it. This would be a great ballistic windshield material.

"We want to find out why this polyurethane works the way it does. Theoretically, no one understood why this particular kind of material – which has nanoscale features of glassy and rubbery domains – would be so good at dissipating energy," he said.

One problem, Thomas said, is that cutting the polymer to analyze it on the nanoscale "would take days." The researchers sought a model material that would react similarly at the nanoscale and could be analyzed much faster. They found one in a polystyrene-polydimethylsiloxane diblock-copolymer. The material self-assembles into alternating 20-nanometer layers of glassy and rubbery polymers. Under a scanning electron microscope, it looks like corduroy; after the test, the disruption pattern from impact can be clearly seen.

The results showed several expected deformation mechanisms and the unexpected result that for sufficiently high velocities, the layered material melted into a homogeneous liquid that seemed to help arrest the projectile and, like the polymer, seal its entry path. The copolymer also behaved differently depending on where the spheres hit. The material showed the best ability to dissipate the energy of impact when spheres were fired perpendicular to the layers, Thomas said.

Testing their ideas took special equipment. The research team came up with a miniaturized test method, dubbed the laser-induced projectile impact test (LIPIT), that uses a laser pulse to fire glass spheres about 3 microns in diameter. The spheres sit on one side of a thin absorbing film facing the target. When a pulse hits the film, the energy causes it to vaporize and the spheres to fly off, hitting speeds between .5 and 5 kilometers per second. Since the kinetic energy scales with velocity squared, the factor of 10 in speed translates to a factor of 100 in impact energy, Thomas said.

Lee calculated the impact in real-world terms: The spheres strike their target 2,000 times faster than an apple falling one meter hits the ground, but with a million times less force. However, because the sphere's impact area is so concentrated, the impact energy is more than 760 times greater. That leaves a mark, he said.

The team tested their materials in two ways: horizontally, with the impact perpendicular to the micro grain, and vertically, straight into the layered edges. They found the horizontal material best at stopping projectiles, perhaps because the layers reflect part of the incident shock wave. Beyond the melt zone in front of the projectile, the layers showed the ability to deform without breaking, which led to improved energy absorption.

"After the impact we can go in and cross-section the structure and see how deep the bullet got, and see what happened to these nice parallel layers," Thomas said. "They tell the story of the evolution of penetration of the projectile and help us understand what mechanisms, at the nanoscale, may be taking place in order for this to be such a great, high-performance, lightweight protection material."

Thomas would like to extend LIPIT testing to other lightweight, nanostructured materials like boron nitride, carbon nanotube-reinforced composites and graphite and graphene-based materials. The ultimate goal, he said, is to accelerate the design of metamaterials with precise control of their nano- and microstructures for a variety of applications.

Co-authors of the paper are graduate students David Veysset, Jonathan Singer, Gagan Saini and Keith Nelson at MIT; Markus Retsch of MIT and the University of Bayreuth, Germany; and Tomas Pezeril of MIT and the Université du Maine, Le Mans, France.

The research was supported by the U.S. Army Research Office.

Researchers at Rice University have developed a lithium-ion battery that can be painted on virtually any surface.

The rechargeable battery created in the lab of Rice materials scientist Pulickel Ajayan consists of spray-painted layers, each representing the components in a traditional battery. The research appears today in Nature’s online, open-access journal Scientific Reports.

“This means traditional packaging for batteries has given way to a much more flexible approach that allows all kinds of new design and integration possibilities for storage devices,” said Ajayan, Rice’s Benjamin M. and Mary Greenwood Anderson Professor in Mechanical Engineering and Materials Science and of chemistry. “There has been lot of interest in recent times in creating power sources with an improved form factor, and this is a big step forward in that direction.”

Lead author Neelam Singh, a Rice graduate student, and her team spent painstaking hours formulating, mixing and testing paints for each of the five layered components – two current collectors, a cathode, an anode and a polymer separator in the middle.

The materials were airbrushed onto ceramic bathroom tiles, flexible polymers, glass, stainless steel and even a beer stein to see how well they would bond with each substrate.

In the first experiment, nine bathroom tile-based batteries were connected in parallel. One was topped with a solar cell that converted power from a white laboratory light. When fully charged by both the solar panel and house current, the batteries alone powered a set of light-emitting diodes that spelled out “RICE” for six hours; the batteries provided a steady 2.4 volts.

The researchers reported that the hand-painted batteries were remarkably consistent in their capacities, within plus or minus 10 percent of the target. They were also put through 60 charge-discharge cycles with only a very small drop in capacity, Singh said.

Each layer is an optimized stew. The first, the positive current collector, is a mixture of purified single-wall carbon nanotubes with carbon black particles dispersed in N-methylpyrrolidone. The second is the cathode, which contains lithium cobalt oxide, carbon and ultrafine graphite (UFG) powder in a binder solution. The third is the polymer separator paint of Kynar Flex resin, PMMA and silicon dioxide dispersed in a solvent mixture. The fourth, the anode, is a mixture of lithium titanium oxide and UFG in a binder, and the final layer is the negative current collector, a commercially available conductive copper paint, diluted with ethanol.

“The hardest part was achieving mechanical stability, and the separator played a critical role,” Singh said. “We found that the nanotube and the cathode layers were sticking very well, but if the separator was not mechanically stable, they would peel off the substrate. Adding PMMA gave the right adhesion to the separator.” Once painted, the tiles and other items were infused with the electrolyte and then heat-sealed and charged.

Singh said the batteries were easily charged with a small solar cell. She foresees the possibility of integrating paintable batteries with recently reported paintable solar cells to create an energy-harvesting combination that would be hard to beat. As good as the hand-painted batteries are, she said, scaling up with modern methods will improve them by leaps and bounds. “Spray painting is already an industrial process, so it would be very easy to incorporate this into industry,” Singh said.

The Rice researchers have filed for a patent on the technique, which they will continue to refine. Singh said they are actively looking for electrolytes that would make it easier to create painted batteries in the open air, and they also envision their batteries as snap-together tiles that can be configured in any number of ways.

“We really do consider this a paradigm changer,” she said.

Co-authors of the paper are graduate students Charudatta Galande and Akshay Mathkar, alumna Wei Gao, now a postdoctoral researcher at Los Alamos National Laboratory, and research scientist Arava Leela Mohana Reddy, all of Rice; Rice Quantum Institute intern Andrea Miranda; and Alexandru Vlad, a former research associate at Rice, now a postdoctoral researcher at the Université Catholique de Louvain, Belgium.

The Advanced Energy Consortium, the National Science Foundation Partnerships for International Research and Education, Army Research Laboratories and Nanoholdings Inc. supported the research.

For more information, visit: www.nature.com/srep/2012/120628/srep00481/full/srep00481.html

An international team of computing experts from the United States, Switzerland and Singapore has created a breakthrough technique for doubling the efficiency of computer chips simply by trimming away the portions that are rarely used.

"I believe this is the first time someone has taken an integrated circuit and said, 'Let's get rid of the part that we don't need,'" said principal investigator Krishna Palem, the Ken and Audrey Kennedy Professor of Computing at Rice University in Houston, who holds a joint appointment at Nanyang Technological University (NTU) in Singapore. "What we've shown is that we can boost performance and cut energy use simultaneously if we prune the unnecessary portions of the digital application-specific integrated circuits that are typically used in hearing aids, cameras and other multimedia devices."

Palem, who heads the Rice-NTU Institute for Sustainable and Applied Infodynamics (ISAID), and his collaborators at Switzerland's Center for Electronics and Microtechnology (CSEM) are unveiling the new pruning technique this week in Grenoble, France, at DATE11, the premier European conference on the design, automation and testing of microelectronics.

Pruning is the latest example of "inexact hardware," the key approach that ISAID is exploring with CSEM to produce the next generation of energy-stingy microchips.

The probabilistic concept is deceptively simple: Slash power demands on microprocessors by allowing them to make mistakes. By cleverly managing the probability of errors and by limiting which calculations produce errors, the designers have found they can simultaneously cut energy demands and boost performance.

At DATE11, Rice graduate student Avinash Lingamneni will describe "probabilistic pruning," the novel technique the team created for trimming away the least-used portions of integrated circuits. Lingamneni used the method to create prototype chips at CSEM. The test prototypes contain both traditional circuits and pruned circuits that were produced side by side on the same silicon chip.

"Our initial tests indicate that the pruned circuits will be at least two times faster, consume about half the energy and take up about half the space of the traditional circuits," Lingamneni said. He said he hopes that the system performs even better in the final tests, which are still under way.

Christian Enz, who leads the CSEM arm of the collaboration and is a co-author of the DATE study, said, "The cost for these gains is an 8 percent error magnitude, and to put that into context, we know that many perceptive types of tasks found in vision or hearing applications can easily tolerate error magnitudes of up to 10 percent."

Palem said the next hurdle for "pruning" will be to use the technique to create a complete prototype chip for a specific application. Lingamneni said he hopes to start designing just such a chip for a hearing aid this summer.

"Based on what we already know, we believe probabilistic computing can produce application-specific integrated circuits for hearing aids that can run four to five times longer on a set of batteries than current hearing aids," Palem said. "The collaboration between ISAID and CSEM was key to achieving these results."

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