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Fall 2019

March of the Atoms

Tracking atomic motion during a reaction provides insight into battery materials

Catherine Wise

Imagine you’re at a football game. It’s halftime, and the marching band is performing, moving seamlessly as a unit in time with the music. From your seat in the bleachers, you can recognize the patterns and shapes that the band is forming, but you cannot determine the role of each individual band member in creating these effects.

Scientists studying the reactivity of electrode materials used in batteries often face similar challenges. Common experimental techniques provide a “spectator viewpoint,” only showing overall changes in a material’s structure as it undergoes a chemical reaction. Some specialized techniques can distinguish smaller scale structural changes, but they are still unable to identify specific atoms—or “band members”—and their interactions. Researchers at the Center for Mesoscale Transport Properties (m2M/t) recently developed a new method that overcomes these limitations, combining multiple techniques in a single instrument to enable correlation of structural changes with the movements of individual atoms as a reaction progresses. Such atomic-level understanding could facilitate the development of more efficient and robust battery materials.

Using an electrochemical cell with magnetite (or any single crystal) and lithium metal as electrodes, electron diffraction and imaging data can be collected to monitor an electrochemical reaction in the single crystal. Figure adapted from Zhang et al. Nature Communications. 2019, 10, 1972.

The method examines electrochemical reactions in a single crystal using electron diffraction and atomic imaging techniques. Applying a voltage to the crystal initiates the electrochemical reaction. Electron diffraction patterns collected at different stages of the reaction provide information about how the crystal structure changes during the reaction. Correlation of these diffraction patterns with atomic imaging data allows specific atoms to be identified and their location to be tracked throughout the reaction.

The researchers at m2M/t used this method to study magnetite, a material comprised of iron and oxygen atoms (Fe3O4). Magnetite is a promising material for use in lithium-ion batteries, in part because of its high cyclability. In other words, the material can add and remove lithium without undergoing irreversible structural changes that reduce battery life.

Previous research found that adding lithium to magnetite led to the formation of iron nanoparticles and lithium oxide. However, exactly how these structural phases formed or why their formation did not cause magnetite to degrade remained unknown. Scientists at m2M/t sought to address these questions by applying their new method to investigate lithium insertion into magnetite.

By examining electron diffraction data, the researchers found that the conversion of magnetite to iron nanoparticles and lithium oxide occurs through two pathways with different intermediate phases. The first pathway had previously been identified in studies of randomly oriented powder or polycrystalline samples, but the second had never been observed before this study. The researchers attributed this new observation to their ability to monitor the reaction in single crystal samples, which have a better-defined local structure than polycrystalline materials. Additionally, the data suggested that the formation of these intermediate phases does not alter the global structural framework of magnetite. In the marching band analogy, it would be as if the movement of individual band members did not change the overall band formation, and therefore spectators could not notice any differences.

Migration of lithium (green) and iron (brown) atoms within the oxygen framework (gray) in magnetite during electrochemical reaction. Image courtesy of Lisa Jansson | Brookhaven National Lab.

Correlating the electron diffraction results with atomic imaging data provided more evidence towards the conclusion that local atomic motion did not cause global structural changes. The researchers were able to follow the movement of individual iron, lithium, and oxygen atoms within the material as its lithium content increased during the reaction. They found that the iron and lithium atoms migrated to different locations within the crystalline framework, but the oxygen atoms remained in place, preserving the structural integrity of the material. The ability to observe such atomic-level structural changes is akin to experiencing a marching band performance from the viewpoint of a band member. Changes to the positioning of a few instruments can be heard by those nearby, even if they are indistinguishable for spectators in the bleachers.

The coupling of electron diffraction and atomic imaging techniques gives “spectator” and “band member” viewpoints simultaneously, allowing researchers to observe both global and local structural changes in a material during an electrochemical reaction. Connecting observations from the two perspectives is crucial for fully understanding the reactivity of a material and improving its performance.

Using this method to study lithium insertion into magnetite, researchers at m2M/t found that the migration of iron and lithium atoms during the reaction does not significantly alter the overall structure of the material. This result helps to explain the well-known high cyclability of magnetite and provides fundamental insight into how to design more efficient lithium-ion batteries. Furthermore, the experimental method can be used to study reactions in other battery materials, such as metal oxides, sulfides, and fluorides, making it broadly valuable for research on electrochemical energy conversion and storage.

More Information

Zhang W, Y Li, L Wu, Y Duan, K Kisslinger, C Chen, DC Bock, F Pan, Y Zhu, AC Marschilok, ES Takeuchi, KJ Takeuchi, and F Wang. 2019. Multi-electron Transfer Enabled by Topotactic Reaction in Magnetite. Nature Communications 10:1972. DOI: 10.1038/s41467-019-09528-9.

Acknowledgments

This work was supported as a part of the Center for Mesoscale Transport Properties, an Energy Frontier Research Center supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, under award No. DE-SC0012673.

Two co-authors were supported by the U.S. Department of Energy, Basic Energy Science, Division of Materials Science and Engineering, under Contract No. DE-SC0012704. Several experimental measurements were performed at the Center for Functional Nanomaterials, Brookhaven National Laboratory, and supported by the U.S. Department of Energy, Basic Energy Sciences, under Contract No. DE-SC0012704.

About the author(s):

  • Catherine Wise is a Ph.D. candidate in the Department of Chemistry at Yale University and a member of the Center for Molecular Electrocatalysis Energy Frontier Research Center. Her research in Prof. James Mayer’s lab involves the study of proton-coupled electron transfer processes in electrochemical systems.

More Information

Zhang W, Y Li, L Wu, Y Duan, K Kisslinger, C Chen, DC Bock, F Pan, Y Zhu, AC Marschilok, ES Takeuchi, KJ Takeuchi, and F Wang. 2019. Multi-electron Transfer Enabled by Topotactic Reaction in Magnetite. Nature Communications 10:1972. DOI: 10.1038/s41467-019-09528-9.

Disclaimer: The opinions in this newsletter are those of the individual authors and do not represent the views or position of the Department of Energy.