Mapping of Silver Matrix Formation in Batteries Will Enhance Efficiency
Stony Brook and Brookhaven scientists detail their pioneering x-ray techniques in Science paper
Study collaborators clockwise from bottom left: Amy Marschilok (SBU), David Bock (SBU), Kevin Kirshenbaum (BNL), Kenneth Takeuchi (BNL), and Zhong Zhong (BNL); ), and Esther Takeuchi (BNL & SBU) at the XPD beamline of the National Synchrotron Light Source II, where future experiments may build on their research.
STONY BROOK, N.Y., January 8, 2015 – Scientists at Stony Brook University and the U.S. Department of Energy’s Brookhaven National Laboratory are using pioneering x-ray techniques to map internal atomic transformations of the highly conductive silver matrix formation within lithium-based batteries that may lead to the design of more efficient batteries. Their findings are published online today in the journal Science .
In a promising lithium-based battery, the formation of a silver matrix transforms a material otherwise plagued by low conductivity. To optimize these multi-metallic batteries—and enhance the flow of electricity—scientists need a way to see where, when, and how these silver, nanoscale “bridges” emerge. In the research paper, the Stony Brook and Brookhaven Lab team successfully mapped this changing atomic architecture and revealed its link to the battery’s rate of discharge. The study 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 in the Department of Materials Science and Engineering 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—known as SVOP—exhibits the high stability, high voltage, and spontaneous matrix formation central to the research and potentially useful in implantable medical devices.
“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.
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 high-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.
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. The team plans to use this new source to continue their battery research.
“We are currently working on other materials that form conductive networks and hope to study them as functioning cells,” coauthor Kenneth 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 Basic Energy Sciences.