Compact batteries enhanced by spontaneous silver matrix formations

Optical images of the non-discharged cathode, showing key differences in the lithium-facing and steel-facing sides. Credit: Image courtesy of Brookhaven National Laboratory

In a promising lithium-based battery, the formation of a highly conductive silver matrix transforms a material otherwise plagued by low conductivity. To optimize these multi-metallic batteries -- and enhance the flow of electricity -- scientists needed a way to see where, when, and how these silver, nanoscale "bridges" emerge.

Now, researchers from the U.S. Department of Energy's Brookhaven National Laboratory and Stony Brook University have used x-rays to map this changing atomic architecture and revealed its link to the battery's rate of discharge. The study -- published online Jan. 8, 2015, in the journal Science -- shows that a slow discharge rate early in the battery's life creates a more uniform and expansive conductive network, suggesting new design approaches and optimization techniques.

"Armed with this insight into battery cathode discharge processes, we can target new materials designed to address critical battery issues associated with power and efficiency," said study coauthor Esther Takeuchi, a SUNY Distinguished Professor at Stony Brook University and Chief Scientist in Brookhaven Lab's Basic Energy Sciences Directorate.

The scientists used bright x-ray beams at Brookhaven Lab's National Synchrotron Light Source (NSLS) -- a DOE Office of Science User Facility -- to probe lithium batteries with silver vanadium diphosphate (Ag2VP2O8) electrodes. This promising cathode material, which may be useful in implantable medical devices, exhibits the high stability, high voltage, and spontaneous matrix formation central to the research.

"The experimental work -- in particular the in-situ x-ray diffraction in batteries totally encased in stainless steel -- should prove useful for industry as it can penetrate prototype and production-level batteries to track their structural evolution during operation," Takeuchi said.

Into the matrix

As these single-use batteries -- synthesized and assembled by Stony Brook graduate student David Bock -- discharge, the lithium ions stored in the anode travel to the cathode, displacing silver ions along the way. The displaced silver then combines with free electrons and unused cathode material to form the conductive silver metal matrix, acting as a conduit for the otherwise impeded electron flow.

"To visualize the cathode processes within the battery and watch the silver network take shape, we needed a very precise system with huseigh-intensity x-rays capable of penetrating a steel battery casing," said study coauthor and Stony Brook University Research Associate Professor Amy Marschilok. "So we turned to NSLS."

Energy dispersive x-ray diffraction (EDXRD) at NSLS provided this real-time -- in situ -- visualization data. In EDXRD, intense beams of x-rays passed through the sample, losing energy as the battery structure bent the beams. Each set of detected beam angles, like time-lapse images, revealed the shifting chemistry as a function of battery discharge.

"The silver forms in particles spanning less than 10 nanometers, and the diffraction patterns can be both dense and faint," said Brookhaven Lab scientist Zhong Zhong, who performed the critical alignment for the x-ray experiments at NSLS.

Once the data was collected, Brookhaven Lab postdoctoral researcher and study coauthor Kevin Kirshenbaum led the data analysis effort.

"This kind of analysis and interpretation requires considerable time and expertise, but the results can be stunning," Kirshenbaum said.

Surprises written in silver

In most batteries, the speed of lithium-ion diffusion determines the rate of discharge, a key factor in overall performance and efficiency. The material closest to the lithium anode would ordinarily discharge first, as the ions have a shorter distance to travel. In a surprising discovery, the researchers found that the material farthest from the anode and nearest the coin cell surface discharged first in the battery.

"This is because the non-discharged cathode material is a very poor electric conductor, so the resistance for lithium ion diffusion is less than for electron flow," said coauthor and SUNY Distinguished Teaching Professor Kenneth Takeuchi. "This highlights a uniquely efficient aspect of in situ silver matrix formation: The silver matrix forms primarily where needed, which is more efficient than using conductive additives."

The in situ diffraction data was combined with two techniques applied after operation: x-ray absorption spectroscopy (XAS) and angle-resolved x-ray diffraction (XRD).

Spectroscopy can reveal exact chemistry because each element absorbs and emits light uniquely, but the x-rays used for XAS cannot penetrate the battery casing. So after each step in the discharge, the researchers removed the cathode and ground it into a powder to measure the average elemental composition. Chia-Ying Lee of the University at Buffalo prepared the reduced cathode materials for the initial ex situ measurements.

"These techniques provide complementary data: the in situ diffraction shows where the silver is formed within the cathode, while the spectroscopy shows more precisely how much silver was formed," Esther Takeuchi said.

Brighter lights and better batteries

NSLS ended its 32-year experimental run in September 2014, but its powerful successor is 

already taking data at Brookhaven Lab. The National Synchrotron Light Source II (NSLS-II) provides beams 10,000 times brighter than NSLS, and in situ energy research is a major part of its mission. NSLS-II, also a DOE Office of Science User Facility, will soon welcome users from industry, academia, and other national labs.

"We are currently working on other materials that form conductive networks and hope to study them as functioning cells," Takeuchi said. "The brighter beams and greater spatial resolution of NSLS-II will be a great tool in studying other cathodes and pushing this technology forward."

This research was funded by the U.S. Department of Energy's Office of Science.

Source: Brookhaven National Laboratory

Cost of cloud brightening for cooler planet revealed

University of Manchester scientists have identified the most energy-efficient way to make clouds more reflective to the sun in a bid to combat climate change. Credit: © magann / Fotolia

Marine Cloud Brightening is a reversible geoengineering method proposed to mitigate rising global temperatures. It relies on propelling a fine mist of salt particles high into the atmosphere to increase the albedo of clouds -- the amount of sunlight they reflect back into space. This would then reduce temperatures on the surface, as less sunlight reaches Earth.
Clouds form when water droplets gather on dust or other particles in the air. Increasing the amount of salt particles in the atmosphere allows more of these water droplets to form, making the clouds denser and therefore more reflective.

A new paper, published in the journal Philosophical Transactions of the Royal Society A, has looked at four different ways of getting the particles into the sky, to compare how effective they may be. The researchers found that a technique called the 'Rayleigh Jet' proved to be best.

Named after Lord Rayleigh, who provided the theory, the technique relies on spraying a fine jet of water that breaks down into small droplets into the sky. The liquid droplets evaporate quickly, leaving behind just the salt particles.

These particles, say the paper's authors, could be generated from specially built ships that could travel the world's oceans spraying salt particles into the air where they then hang in the atmosphere for several days until they return to Earth as rain.

Previous studies have optimised the size of the salt particles needed to produce the best increase in cloud reflectance but haven't taken into account how much energy the technique would need and how much it would cost to operate. This new paper, by teams at the universities of Manchester, Washington and Edinburgh, tackled this question. The researchers tested each technique so there was an increase in reflection of 5%, a figure that would combat the predicted effects of increased carbon dioxide levels over the rest of this century. They then looked at how much energy each would consume.

The scientists say that the Rayleigh jet method could produce the desired effect using 30 megawatts of energy, about the same energy that two large ships produce.

Dr Paul Connolly, based in the School of Earth, Atmospheric and Environmental Sciences at The University of Manchester, said: "It can be incredibly energy intensive to propel water high into the atmosphere and the energy required had never really been tested before. Our paper optimises the salt particle sizes to produce the required change in cloud reflectance for the least energy cost. It is an important finding if these techniques should be needed in the future.

"I am not recommending that we use any of these techniques now, but it is important to know how best to use them should they become necessary. Should no progress be made to reduce CO2 levels, then geoengineering techniques, similar to this, might become necessary to avoid dangerous rises in global temperatures."

Source: Manchester University

The Three years since Japan's disaster: Communities remain scattered and suffering

While western eyes are focused on the ongoing problems of the Fukushima Daiichi nuclear reactor site, thousands of people are still evacuated from their homes in north-eastern Japan following the earthquake, tsunami and nuclear emergency. Many are in temporary accommodation and frustrated by a lack of central government foresight and responsiveness to their concerns.

With the exception of the ongoing problems at the Fukushima Daiichi nuclear reactor, outside of the Tohoku region of Japan, the after effects of the Great East Japan Earthquake of 2011, and the subsequent tsunami and nuclear disaster, are no longer front page news. The hard work of recovery is the everyday reality in the region, and for planning schools and consultants across the country the rebuilding of Tohoku dominates practice and study.

But while physical reconstruction takes place, progress is not smooth. Many victims of the disasters and members of the wider public feel that the government is more interested in feeding the construction industry than addressing the complex challenges of rebuilding sustainable communities. This is a region that was already suffering from the challenges of an aging population, the exodus of young people to Tokyo and the decline of traditional fisheries-based industries. In the worst cases people are facing the invidious choice of returning to areas that are still saturated with radioactive fallout or never going home.

The frustration is reflected in four short pieces in Planning Theory and Practice's Interface Section from architecture, design and planning practitioners working with communities in four different parts of Tohoku.

Christian Dimmer, Assistant Professor at Tokyo University and founder of TPF2 -- Tohoku Planning Forum which links innovative redevelopment schemes in the region says:

"The current Japanese government's obsession with big construction projects, like mega-seawalls that have already been shown to be not likely to be effective, is leading to really innovative community solutions being marginalized, the voices of communities being ignored, and sustainability cast aside."
According to community planner and academic, Kayo Murakami -- who edits this Interface section: "The troubles of the Tohoku reconstruction are not just a concern for Japan. They highlight some of the fundamental challenges for disaster recovery and building sustainable communities, in which people are really involved, all over the world."

Source: Taylor & Francis

The Floating nuclear plants could ride out tsunamis: New design for enhanced safety, easier siting and centralized construction

This illustration shows a possible configuration of a floating offshore nuclear plant, based on design work by Jacopo Buongiorno and others at MIT's Department of Nuclear Science and Engineering. Like offshore oil drilling platforms, the structure would include living quarters and a helipad for transportation to the site.
Credit: Illustration courtesy of Jake Jurewicz/MIT-NSE

When an earthquake and tsunami struck the Fukushima Daiichi nuclear plant complex in 2011, neither the quake nor the inundation caused the ensuing contamination. Rather, it was the aftereffects -- specifically, the lack of cooling for the reactor cores, due to a shutdown of all power at the station -- that caused most of the harm.

A new design for nuclear plants built on floating platforms, modeled after those used for offshore oil drilling, could help avoid such consequences in the future. Such floating plants would be designed to be automatically cooled by the surrounding seawater in a worst-case scenario, which would indefinitely prevent any melting of fuel rods, or escape of radioactive material.

The concept is being presented this week at the Small Modular Reactors Symposium, hosted by the American Society of Mechanical Engineers, by MIT professors Jacopo Buongiorno, Michael Golay, and Neil Todreas, along with others from MIT, the University of Wisconsin, and Chicago Bridge and Iron, a major nuclear plant and offshore platform construction company.

Such plants, Buongiorno explains, could be built in a shipyard, then towed to their destinations five to seven miles offshore, where they would be moored to the seafloor and connected to land by an underwater electric transmission line. The concept takes advantage of two mature technologies: light-water nuclear reactors and offshore oil and gas drilling platforms. Using established designs minimizes technological risks, says Buongiorno, an associate professor of nuclear science and engineering (NSE) at MIT.

Although the concept of a floating nuclear plant is not unique -- Russia is in the process of building one now, on a barge moored at the shore -- none have been located far enough offshore to be able to ride out a tsunami, Buongiorno says. For this new design, he says, "the biggest selling point is the enhanced safety."

A floating platform several miles offshore, moored in about 100 meters of water, would be unaffected by the motions of a tsunami; earthquakes would have no direct effect at all. Meanwhile, the biggest issue that faces most nuclear plants under emergency conditions -- overheating and potential meltdown, as happened at Fukushima, Chernobyl, and Three Mile Island -- would be virtually impossible at sea, Buongiorno says: "It's very close to the ocean, which is essentially an infinite heat sink, so it's possible to do cooling passively, with no intervention. The reactor containment itself is essentially underwater."
Buongiorno lists several other advantages. For one thing, it is increasingly difficult and expensive to find suitable sites for new nuclear plants: They usually need to be next to an ocean, lake, or river to provide cooling water, but shorefront properties are highly desirable. By contrast, sites offshore, but out of sight of land, could be located adjacent to the population centers they would serve. "The ocean is inexpensive real estate," Buongiorno says.

In addition, at the end of a plant's lifetime, "decommissioning" could be accomplished by simply towing it away to a central facility, as is done now for the Navy's carrier and submarine reactors. That would rapidly restore the site to pristine conditions.

This design could also help to address practical construction issues that have tended to make new nuclear plants uneconomical: Shipyard construction allows for better standardization, and the all-steel design eliminates the use of concrete, which Buongiorno says is often responsible for construction delays and cost overruns.

There are no particular limits to the size of such plants, he says: They could be anywhere from small, 50-megawatt plants to 1,000-megawatt plants matching today's largest facilities. "It's a flexible concept," Buongiorno says.

Most operations would be similar to those of onshore plants, and the plant would be designed to meet all regulatory security requirements for terrestrial plants. "Project work has confirmed the feasibility of achieving this goal, including satisfaction of the extra concern of protection against underwater attack," says Todreas, the KEPCO Professor of Nuclear Science and Engineering and Mechanical Engineering.
Buongiorno sees a market for such plants in Asia, which has a combination of high tsunami risks and a rapidly growing need for new power sources. "It would make a lot of sense for Japan," he says, as well as places such as Indonesia, Chile, and Africa.

Source: Massachusetts Institute of Technology