Because X-rays and neutrons are sensitive to electron and nuclear density, they can reveal discontinuities in the electrodes. Photo by T.Arlt, I. Manke/HZB, R. Ziesche/UCL
Feb. 7 (UPI) -- For the first time, scientists have used neutrons and X-rays to study the effects of repeated charge-discharge cycles on electrode surfaces in lithium batteries.
The electrodes in lithium-ion batteries must boast large surface areas to promote rapid charging and powerful discharges, but to fit inside ever-shrinking electronics like smartphones and razor-thin laptops, electrodes must also be small. To meet these two requirements, most lithium battery electrodes are rolled into a cylinder
Because the electrodes are typically tightly coiled, it is difficult to closely observe the aging process inside lithium batteries, the deformations and discontinuities that accumulate as a battery is charged and discharged.
For the new study, scientists married a pair of tomography techniques, using both X-rays and neutrons, to study deformations in aging batteries.
Researchers deployed X-ray tomography at the European Synchrotron Radiation Facility in Grenoble, France, to image the tiny defects that accrue on electrodes during charging cycles.
"Neutron tomography, on the other hand, made it possible to directly observe the migration of lithium ions and also to determine how the distribution of the electrolyte in the battery cell changes over time," Ingo Manke, tomography expert at Helmholtz-Zentrum Berlin in Germany, said in a news release.
Because X-rays and neutrons are sensitive to electron and nuclear density, they can reveal discontinuities in the electrodes. But determining the precise location of these discontinuities is difficult.
Researchers used sophisticated mathematical models to analyze the images and virtually unwind the tightly coiled cylinders of electrodes. This process allowed scientists to more precisely pinpoint microscopic deformations on the electrode surfaces.
"The algorithm was originally meant for virtually unrolling papyrus scrolls," Manke said. "But it can also be used to find out exactly what happens in compact densely wound batteries."
Scientists described their novel imaging efforts in a new paper, published Friday in the journal Nature Communications.
"Virtual electrode unrolling techniques provide a deeper view inside the electrode layers and are used to detect minor fluctuations which are difficult to observe using conventional three dimensional rendering tools," scientists wrote in their paper.
The unwinding process allowed scientists to recognize distinctions between the effects of the charge cycle on different portions of the electrodes. The inner windings, for example, hosted electrochemical activity quite different from the electrochemical patterns observed in the outer windings.
"The process we have developed gives us a unique tool for looking inside a battery during operation and analyzing where and why performance losses occur," Manke said. "This allows us to develop specific strategies for improving the design of wound batteries."
