MSE's Katsuyo Thornton part of team whose Surprising discovery could lead to better batteries

MSE's Katsuyo Thornton part of team whose Surprising discovery could lead to better batteries

Scientists, including Katsuyo Thornton (top right) and Feng Weng of Brookhaven Nat'l Laboratory, have observed how lithium moves inside of individual nanoparticles that make up batteries. The finding could help companies develop longer-lasting batteries.

A collaboration led by scientists at the U.S. Department of Energy’s (DOE) Brookhaven National Laboratory has observed an unexpected phenomenon in lithium-ion batteries—the most common type of battery used to power cell phones and electric cars. As lithium flows into electrodes, the scientists witnessed the concentration of lithium reverse at a certain point, instead of constantly increasing. This discovery, which was published Friday in the journal Science Advances, is a major step toward improving the battery life of consumer electronics.

“If you have a cell phone, you likely need to charge its battery every day, due to the limited capacity of the battery’s electrodes,” said Esther Takeuchi, a SUNY distinguished professor at Stony Brook University and a chief scientist in the Energy Sciences Directorate at Brookhaven Lab. “The findings in this study could help develop batteries that charge faster and last longer.”

Visualizing batteries on the nanoscale

2D maps depict the concentration of lithium inside a single nanoparticle. Over time, the concentration increases, decreases, and then increases again.

Inside every lithium-ion battery are particles whose atoms are arranged in a lattice—a periodic structure with gaps between each atom. When a battery supplies electricity,lithium flow into the lattice and fill the empty spaces. 

“Previously, scientists assumed that the concentration of lithium would continuously increase in the lattice as lithium enters into the particle,” said Wei Zhang, a scientist at Brookhaven’s Sustainable Energy Technologies Department. “But now, we have seen that this may not be true when the battery’s electrodes are made from nano-sized particles. We observed the lithium concentration within local regions of nanoparticles go up, and then down—it reversed.”

Electrodes are often made from nanoparticles in order to increase a battery’s power density. But scientists have not been able to fully understand how these electrodes work, due to a limited ability to watch them work in action. Now, by combining a unique suite of experimental tools, the scientists were able to image their reactions in real time.

“Just as if you were pouring water into a cup, we can see the overall level of lithium continuously increase inside the nano-sized particle,” said Feng Wang, the leader of this study and a scientist in Brookhaven’s Sustainable Energy Technologies Department. “But unlike water in a cup, which will stay uniform, lithium may preferentially move out of some areas, creating inconsistent levels of lithium across the lattice.” 

The scientists explained that uneven movement of lithium could have lasting, damaging effects because it stains the structure of the active part of batteries and even leads to fatigue failure.

“Before lithium enters the lattice, its structure is very uniform,” Wang said. “But once lithium goes in, it stretches the lattice, and when lithium goes out, the lattice shrinks. So each time you charge and drain a battery, its active component will be stressed, and its quality will degrade over time. However, the lattice change in nano-sized particles is gradual and more coherent, and thus causes less damage than in other battery systems.”

Combining tools of the trade

In order to make these observations, the scientists combined transmission electron microscopy (TEM) experiments—conducted at the Center for Functional Nanomaterials (CFN), a DOE Office of Science User Facility at Brookhaven Lab, and at Brookhaven’s Condensed Matter Physics and Materials Science Department—with x-ray analyses at the National Synchrotron Light Source (NSLS), a DOE Office of Science user facility at Brookhaven that closed in 2014 when its successor, NSLS-II, opened.

“Wang’s team combined TEM with x-ray techniques,” said Yimei Zhu, co-author of the study and a senior physicist at Brookhaven Lab. “Both methods use a similar approach to analyze the structure of materials, but can provide complementary information. Electrons are sensitive to the local structure, while x-rays can probe a larger volume and enable much better statistics.”

The team has also developed a model that could simulate the processes observed experimentally to understand why lithium concentration reversal arises. The use of the model made it possible to examine how lithium moves within an individual nanoparticle and test hypothesis for the underlying mechanisms of the concentration reversal. The simulations were conducted at U-M. MSE Professor Katsuyo Thornton, a participant of the NorthEast Center for Chemical Energy Storage, led the theoretical effort. She emphasized the critical role computer modeling and simulations played in this work. 

“We initially thought that the mechanism for the reversal was similar to those previously proposed, which stemmed from the interactions between nearby particles. However, it turned out a reversal within a single particle could not be reproduced and required a different mechanism. Simulations were critical in this work because, without it, we would have made a wrong conclusion.” While the study focused on lithium-ion batteries, the scientists say the observed phenomenon may also occur in other high-performance battery materials. 

“Down the road, we plan to use state-of-the-art facilities at CFN and NSLS-II to more closely examine how battery materials work, and to find solutions to build new batteries that can charge faster and last longer,” Wang said. “These facilities offer the ideal tools for imaging the structure of battery materials in real time and under real-world conditions.”

This study was supported by the DOE Office of Science and Brookhaven’s Laboratory Directed Research and Development program. Two DOE Office of Science Energy Frontier Research Centers, the NorthEast Center for Chemical Energy Storage and the Center for Mesoscale Transport Properties, supported the project, and computational resources were provided by the National Energy Research Scientific Computer Center, a DOE Office of Science User Facility at Lawrence Berkeley National Laboratory. Additional support was provided by the National Science Foundation, National Key R&D Program of China, the Strategic Priority Research Program of Chinese Academy of Sciences, and the University of Michigan Advanced Research Computing. For a complete list of supporting and collaborating institutions, please see the scientific paper.

Related Links

 Scientific Paper: “Localized concentration reversal of lithium during intercalation into nanoparticles

 Press Release: “Scientists Capture Lithium-Ion Batteries in Nanoscale Action”