Tag Archives: SLAC National Accelerator Laboratory

Keeping it together—new glue for lithium-ion batteries

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Glue isn’t the first component that comes to my mind when discussing ways to make lithium-ion (Li-ion) batteries more efficient but researchers at SLAC National Accelerator Laboratory at Stanford University have proved that the glue used to bind a Li-ion battery together can make a difference to its efficiency (from the Aug. 20, 2013 news item on phys.org),

When it comes to improving the performance of lithium-ion batteries, no part should be overlooked – not even the glue that binds materials together in the cathode, researchers at SLAC and Stanford have found.

Tweaking that material, which binds lithium sulfide and carbon particles together, created a cathode that lasted five times longer than earlier designs, according to a report published last month in Chemical Science. The research results are some of the earliest supported by the Department of Energy’s Joint Center for Energy Storage Research.

“We were very impressed with how important this binder was in improving the lifetime of our experimental battery,” said Yi Cui, an associate professor at SLAC and Stanford who led the research.

The Aug. 19, 2013 SLAC news release by Mike Ross, which originated the news item, provides context for this accidental finding about glue and Li-ion batteries,

Researchers worldwide have been racing to improve lithium-ion batteries, which are one of the most promising technologies for powering increasingly popular devices such as mobile electronics and electric vehicles. In theory, using silicon and sulfur as the active elements in the batteries’ terminals, called the anode and cathode, could allow lithium-ion batteries to store up to five times more energy than today’s best versions. But finding specific forms and formulations of silicon and sulfur that will last for several thousand charge-discharge cycles during real-life use has been difficult.

Cui’s group was exploring how to create a better cathode by using lithium sulfide rather than sulfur. The lithium atoms it contains can provide the ions that shuttle between anode and cathode during the battery’s charge/discharge cycle; this in turn means the battery’s other electrode can be made from a non-lithium material, such as silicon. Unfortunately, lithium sulfide is also electrically insulating, which greatly reduces any battery’s performance. To overcome this, electrically conducting carbon particles can be mixed with the sulfide; a glue-like material – the binder – holds it all together.

Scientists in Cui’s [Yi Cui, an associate professor at SLAC and Stanford who led the research] group devised a new binder that is particularly well-suited for use with a lithium sulfide cathode ­– and that also binds strongly with intermediate polysulfide molecules that dissolve out of the cathode and diminish the battery’s storage capacity and useful lifetime.

The experimental battery using the new binder, known by the initials PVP, retained 94 percent of its original energy-storage capacity after 100 charge/discharge cycles, compared with 72 percent for cells using a conventionally-used binder, known as PVDF. After 500 cycles, the PVP battery still had 69 percent of its initial capacity.

Cui said the improvement was due to PVP’s much stronger affinity for lithium sulfide; together they formed a fine-grained lithium sulfide/carbon composite that made it easier for lithium ions to penetrate and reach all of the active material within the cathode. In contrast, the previous binder, PVDF, caused the composite to grow into large clumps, which hindered the lithium ions’ penetration and ruined the battery within 100 cycles

Even the best batteries lose some energy-storage capacity with each charge/discharge cycle. Researchers aim to reduce such losses as much as possible. Further enhancements to the PVP/lithium sulfide cathode combination will be needed to extend its lifetime to more than 1,000 cycles, but Cui said he finds it encouraging that improving the usually overlooked binder material produced such dramatic benefits.

Here’s a link to and a citation for the published paper,

Stable cycling of lithium sulfide cathodes through strong affinity with a bifunctional binder by Zhi Wei Seh, Qianfan Zhang, Weiyang Li, Guangyuan Zheng, Hongbin Yaoa, and Yi Cui. Chem. Sci., 2013,4, 3673-3677 DOI: 10.1039/C3SC51476E First published online 11 Jul 2013

There’s a note on the website stating the article is free but the instructions for accessing the article are confusing seeming to suggest you need a subscription of some sort or you need to register for the site.

I have written about Yi Cui’s work with lithium-ion batteries before including this Jan. 9, 2013 posting, How is an eggshell like a lithium-ion battery?, which also features a news release by Mike Ross.

Only for the truly obsessed: a movie featuring gold nanocrystal vibrations

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Folks at the London Centre for Nanotechnology (at the University College of London) have released a film made with a pioneering 3D imaging technique that shows how gold nanocrystals vibrate. From the May 23, 2013 news release on EurekAlert,

A billon-frames-per-second film has captured the vibrations of gold nanocrystals in stunning detail for the first time.

The film, which was made using 3D imaging pioneered at the London Centre for Nanotechnology (LCN) at UCL [University College of London], reveals important information about the composition of gold. The findings are published in the journal Science.

Jesse Clark, from the LCN and lead author of the paper said: “Just as the sound quality of a musical instrument can provide great detail about its construction, so too can the vibrations seen in materials provide important information about their composition and functions.”

“It is absolutely amazing that we are able to capture snapshots of these nanoscale motions and create movies of these processes. This information is crucial to understanding the response of materials after perturbation. “

Caption: The acoustic phonons can be visualized on the surface as regions of contraction (blue) and expansion (red). Also shown are two-dimensional images comparing the experimental results with theory and molecular dynamics simulation. The scale bar is 100 nanometers. Credit: Jesse Clark/UCL

Caption: The acoustic phonons can be visualized on the surface as regions of contraction (blue) and expansion (red). Also shown are two-dimensional images comparing the experimental results with theory and molecular dynamics simulation. The scale bar is 100 nanometers. Credit: Jesse Clark/UCL

Here are more details from the news release,

Scientists found that the vibrations were unusual because they start off at exactly the same moment everywhere inside the crystal. It was previously expected that the effects of the excitation would travel across the gold nanocrystal at the speed of sound, but they were found to be much faster, i.e., supersonic.

The new images support theoretical models for light interaction with metals, where energy is first transferred to electrons, which are able to short-circuit the much slower motion of the atoms.

The team carried out the experiments at the SLAC National Accelerator Laboratory using a revolutionary X-ray laser called the “Linac Coherent Light Source”. The pulses of X-rays are extremely short (measured in femtoseconds, or quadrillionths of a second), meaning they are able to freeze all motion of the atoms in any sample, leaving only the electrons still moving.

However, the X-ray pulses are intense enough that the team was able to take single snapshots of the vibrations of the gold nanocrystals they were examining. The vibration was started with a short pulse of infrared light.

The real keeners can watch the movie if they click on the link to the May 23, 2013 news release on EurekAlert.

The team developing this movie was international in scope (from the news release),

The research team included contributors from UCL, University of Oxford, SLAC, Argonne National Laboratory [US] and LaTrobe University, Australia.

Soybeans and nanoparticles redux

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If you read the Feb. 6, 2013 news release on EurekAlert too quickly you might not realize that only one of the two types of the tested nanoparticles adversely affects soybean plants,

Two of the most widely used nanoparticles (NPs) accumulate in soybeans — second only to corn as a key food crop in the United States — in ways previously shown to have the potential to adversely affect the crop yields and nutritional quality, a new study has found. It appears in the journal ACS Nano. [emphasis mine]

Jorge L. Gardea-Torresdey and colleagues cite rapid increases in commercial and industrial uses of NPs, the building blocks of a nanotechnology industry projected to put $1 trillion worth of products on the market by 2015. Zinc oxide and cerium dioxide are among today’s most widely used NPs. Both are used in cosmetics, lotions, sunscreens and other products. They eventually go down the drain, through municipal sewage treatment plants, and wind up in the sewage sludge that some farmers apply to crops as fertilizer. Gardea-Torresdey’s team previously showed that soybean plants grown in hydroponic solutions accumulated zinc and cerium dioxide in ways that alter plant growth and could have health implications.

The question remained, however, as to whether such accumulation would occur in the real-world conditions in which farmers grow soybeans in soil, rather than nutrient solution. Other important questions included the relationship of soybean plants and NPs, the determination of their entrance into the food chain, their biotransformation and toxicity and the possible persistence of these products into the next plant generation. Their new study, performed at two world-class synchrotron facilities — the SLAC National Accelerator Laboratory in California and the European Synchrotron Radiation Facility in Grenoble, France, addressed those questions. “To our knowledge, this is the first report on the presence of cerium dioxide and zinc compounds in the reproductive/edible portions of the soybean plant grown in farm soil with cerium dioxide and zinc oxide nanoparticles. In addition, our results have shown that cerium dioxide NPs in soil can be taken up by food crops and are not biotransformed in soybeans. [emphasis mine] This suggests that cerium dioxide NPs can reach the food chain and the next soybean plant generation, with potential health implications,” the study notes.

The University of Texas El Paso Feb. 6, 2013 news release provides more detail and more clarity about the results of the research ,

Experiments led by Jorge Gardea-Torresdey, Ph.D., of The University of Texas at El Paso (UTEP) have shown that certain man-made nanoparticles that land in soil can be transferred from the roots of plants to the grains, thus entering the food supply via crops grown for human consumption.

…

Cerium dioxide, which is commonly used in sunscreens and oil refining, remained intact when it was absorbed by the plant, and was transferred all the way into the edible soybean grains. [emphasis mine]

On the other hand, zinc oxide – commonly used in sunscreens and cosmetics – was transferred to the grain, but had broken down to a nontoxic form. [emphasis mine]

To track the nanoparticles’ route within the plants, the researchers used the intense beams of X-rays from the SLAC National Accelerator Laboratory’s Stanford Synchrotron Radiation Lightsource (SSRL) and the European Synchrotron Radiation Facility (ESRF) in Grenoble, France. The X-rays also helped reveal whether or not the nanoparticles were chemically transformed in the process.

While studies are under way, Gardea-Torresdey says there is currently little information on the potential health implications of nanoparticles.

UTEP has produced a video titled, UTEP Study Shows Engineered Nanoparticles Can Enter Food Supply. This piece, which features Gardea-Torresdey and a student,  seems to be less about the study and more about the benefits of studying at UTEP and the impact of the Latino community in the US,


Here’s a citation and a link to the article (Note: This work bears a remarkable resemblance to the work mentioned in my Aug. 20, 2012 posting about soybeans and nanoparticles, not least because the studies share three or more authors),

In Situ Synchrotron X-ray Fluorescence Mapping and Speciation of CeO2 and ZnO Nanoparticles in Soil Cultivated Soybean (Glycine max) by Jose A. Hernandez-Viezcas, Hiram Castillo-Michel, Joy Cooke Andrews , Marine Cotte , Cyren Rico, Jose R. Peralta-Videa, Yuan Ge, John H. Priester, Patricia Ann Holden, and Jorge L. Gardea-Torresdey. ACS Nano, DOI: 10.1021/nn305196q Publication Date (Web): January 15, 2013

Copyright © 2013 American Chemical Society

The article is behind a paywall.