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

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A new wireless energy transfer device can charge any device without using cables

Researchers have designed a new device for wireless energy transfer that will charge mobile phones or laptops without the need for wires. Credit: UPV

Researchers at the Universitat Politècnica de València (UPV) have designed a new device for wireless energy transfer that will, for example, charge mobile phones or laptops without needing wires.

The system, patented by the UPV, is based on the use of resonators designed with radial photonic crystals; one of them would act as an energy transmitter and the other would be set on the device that needed to be charged. Between them a phenomena known as resonant coupling is produced, which is what finally produces the charging or recharging of the equipment.

"This phenomena is produced when a resonant object is moved closer to a second resonant element and both resonance frequencies are equal or quite similar. This physical proximity produces an energy coupling from the first device, that acts as the source, to the second one, that acts as the charge," says José Sánchez-Dehesa, researcher at the Wave Phenomena 

Group of the Universitat Politècnica de València.

The device could also be used as a power supply system for equipment such as keyboards and wireless mice, speakers, etc. Besides consumer electronics, it could also be used in an industrial environment as power supply for robots or guided vehicles, and bioelectric devices (cardiac pacemakers, defibrillators, etc.)

The UPV researchers' study was released last June in the Annals of Physics magazine. After the first laboratory simulations and calculations of the system's performance, the engineers of the Wave Phenomena Group are now working on the development of the first prototype.

Technology implementation

With regard to the implementation of these devices, UPV researchers say that, "although it may seem futuristic, it is foreseeable that they become universal due to the spread of charging infrastructure in many settings. This technology could follow the same path as WIFI networks," explains Jorge Carbonell, researcher at the Wave Phenomena Group.

Source: Asociación RUVID

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Storing hydrogen underground could boost transportation, energy security

Salt caverns such as the one depicted here could provide a low-cost solution for the geologic storage of hydrogen. The colors in the illustration represent depth, with blue as the deepest part of the cavern and red the most shallow.
Credit: Sandia National Laboratories

Large-scale storage of low-pressure, gaseous hydrogen in salt caverns and other underground sites for transportation fuel and grid-scale energy applications offers several advantages over above-ground storage, says a recent Sandia National Laboratories study sponsored by the Department of Energy's Fuel Cell Technologies Office.

Geologic storage of hydrogen gas could make it possible to produce and distribute large quantities of hydrogen fuel for the growing fuel cell electric vehicle market, the researchers concluded.

Geologic storage solutions can service a number of key hydrogen markets since "costs are more influenced by the geology available rather than the size of the hydrogen market demand," said Sandia's Anna Snider Lord, the study's principal investigator.

The work, Lord said, could provide a roadmap for further research and demonstration activities, such as an examination of environmental issues and geologic formations in major metropolitan areas that can hold gas. Researchers could then determine whether hydrogen gas mixes with residual gas or oil, reacts with minerals in the surrounding rock or poses any environmental concerns.

Storage seen as key to realizing hydrogen's market growth

Should the market demands for hydrogen fuel increase with the introduction of fuel cell electric vehicles, the U.S. will need to produce and store large amounts of cost-effective hydrogen from domestic energy sources, such as natural gas, solar and wind, said Daniel Dedrick, Sandia hydrogen program manager.

As Toyota, General Motors, Hyundai and others move ahead with plans to develop and sell or lease hydrogen fuel cell electric vehicles, practical storage of hydrogen fuel at large scale is nessesary to enable widespread hydrogen-powered transportation infrastructure. Such storage options, Dedrick said, are needed to realize the full potential of hydrogen for transportation.

Additionally, installation of electrolyzer systems on electrical grids for power-to-gas applications, which integrate renewable energy, grid services and energy storage will require large-capacity, cost-effective hydrogen storage.

Storage above ground requires tanks, which cost three to five times more than geologic storage, Lord said. In addition to cost savings, underground storage of hydrogen gas offers advantages in volume. "Above-ground tanks can't even begin to match the amount of hydrogen gas that can be stored underground," she said.
The massive quantities of hydrogen that is stored in geologic features can subsequently be distributed as a high-pressure gas or liquid to supply hydrogen fuel markets.

Model helps identify the most favorable storage locations
While geologic storage may prove to be a viable option, several issues need to be explored, said Lord, including permeability of various geologic formations.

A geologist in Sandia's geotechnology and engineering group, Lord for years has been involved in the geologic storage of the U.S. Strategic Petroleum Reserve, the world's largest emergency supply of crude oil.

For her study on geologic storage, Lord and her colleagues analyzed and reworked the geologic storage module of Argonne National Laboratory's Hydrogen Delivery Scenario Analysis Model. To help refine the model, Lord studied storing hydrogen in salt caverns to meet peak summer driving demand for four cities: Los Angeles, Houston, Pittsburgh and Detroit.

She determined that 10 percent above the average daily demand for 120 days should be stored. She then modeled how much hydrogen each city would need if hydrogen met 10, 25 and 100 percent of its driving fuel needs.

Los Angeles has three times the population of Detroit and more than six and a half times the population of Pittsburgh, but the nearest salt formations are in Arizona, so Lord included the cost of getting the stored hydrogen from Arizona to Los Angeles.

Even so, Los Angeles' modeled costs are significantly less than those for Detroit and Pittsburgh. Salt formations in Arizona are thicker than those for Detroit and Pittsburgh, with larger and fewer caverns. Houston has the best conditions of the four cities because the Gulf Coast offers large, deep salt formations.

To examine the cost of geologic hydrogen storage, Lord started by selecting geologic formations that currently store natural gas. Working with Sandia economist Peter Kobos, Lord analyzed costs to store hydrogen gas in depleted oil and gas reservoirs, aquifers, salt caverns and hard rock caverns.

Their paper, "Geologic storage of hydrogen: Scaling up to meet city transportation demands," was published in the International Journal of Hydrogen Energy.

A geologic solution for peak period storage
Other fuels are already stored geologically. Oil from the Strategic Petroleum Reserve, for example, is held in large man-made caverns along the Gulf Coast. Natural gas is stored in more than 400 geologic sites to meet winter heating demands.

Lord envisions that excess hydrogen produced throughout the year could be brought to geologic storage sites and then piped to cities during the summer, when the demand for driving fuels peaks.

Depleted oil and gas reservoirs and aquifers initially seem the most economically attractive options, she said. "Just looking at numbers, because they can hold such a larger volume relative to any cavern you create, they look cheaper," she said.

But hydrogen gas is a challenging substance to store. "Because it's a smaller molecule than methane, for example, it has the potential to leak easier and move faster through the rock," Lord said.

Depleted oil and gas reservoirs and aquifers could leak hydrogen, and cycling -- filling a storage site, pulling hydrogen out for use and refilling the site -- can't be done more than once or twice a year to preserve the integrity of the rock formation, Lord said.
With a salt cavern or hard rock cavern, "there are no permeability issues, there's really no way anything can leak," she said. "You can bring more product in and out, and that will, in the long run, decrease your costs."

Hard rock caverns are relatively unproven; only one site holds natural gas. But salt caverns, which are created 1,000 to 6,000 feet below ground by drilling wells in salt formations, pumping in undersaturated water to dissolve the salt, then pumping out the resulting brine, are used more extensively and already store hydrogen on a limited scale, Lord said.

Future challenges

Lord said her work could lead to demonstration projects to further cement the viability of underground hydrogen storage. Salt caverns are the logical choice for a pilot project due to their proven ability to hold hydrogen, she said. Environmental concerns such as contamination could also be further analyzed.

However, salt formations are limited. None exist in the Pacific Northwest, much of the East Coast and much of the South, except for the Gulf Coast area. Other options are needed for development of a nationwide hydrogen storage system.

Lord's work adds to Sandia's capabilities and decades of experience in hydrogen and fuel cells systems. Sandia leads a number of other hydrogen research efforts, including the Hydrogen Fueling Infrastructure Research and Station Technology (H2FIRST) project co-led by the National Renewable Energy Laboratory (NREL), a maritime fuel cell demonstration, a development project focused on hydrogen-powered forklifts and a recent study of how many California gas stations can safely store and dispense hydrogen.

Source: Sandia National Laboratories

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