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Sodium-Ion Battery Defects Captured with X-Ray Imaging

Sodium-ion batteries have indeed been heralded as a sustainable alternative to lithium-ion batteries since they are driven by a more abundantly available resource. However, sodium-ion batteries have encountered a significant problem: the cathodes degrade rapidly during recharging.

Sodium-Ion Battery Defects Captured with X-Ray Imaging

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A Cornell-led partnership was successful in finding an elusive mechanism that can cause this degradation—transient crystal defects—by employing a novel type of X-Ray imaging that allowed the researchers to record the fleeting flaws while the battery was in use.

The study was published on April 14th, 2023, in Advanced Energy Materials. The lead author of the study is postdoctoral fellow Oleg Gorobstov.

Andrej Singer, Assistant Professor and David Croll Sesquicentennial Faculty Fellow in Cornell Engineering’s Department of Materials Science and Engineering, is the project’s leader. His group has been studying nanoscale phenomena in energy and quantum materials, frequently using improved operando X-Ray tools.

These methods are particularly useful for investigating the behavior of transient defects, which arise temporarily during ionic transport. As a result, little is known about their life cycle and impact.

In collaboration with researchers from the University of California, San Diego, led by Professor Shirley Meng, and the Advanced Photon Source at the United States Department of Energy’s Argonne National Laboratory, the team focused on the constituent parts of a charging sodium-ion battery, producing real-time 3D snapshots that disclosed the morphology and atomic displacements within NaxNi1-xMnyO2 cathodes.

Operando measurements are indispensable here. If we looked at the battery before and after the first charge-discharge cycle, we would see no defects. But during the operation, we see how the defects form and self-heal, leaving detectable ‘scars’ behind.

Andrej Singer, Assistant Professor, Department of Materials Science and Engineering, Cornell University

To explain what they saw, the researchers looked to metals, where flaws like dislocations allow ductile materials to deform without breaking. The researchers traced the movement of the transient—also known as metastable—imperfections using metallurgical modeling and produced qualitative predictions of the stresses that moved them as the material altered and self-healed.

Dislocations are one-dimensional crystal defects. Their presence in the ceramic cathodes we study is surprising, and the mechanisms for their formation are yet to be understood. We found that the dislocations form at a transiently forming anti-phase domain boundary. This preceding configuration is a new piece of the puzzle that we hope will help us better understand the defect dynamics in this important class of materials,” adds Gorobtsov.

The researchers are now focusing on how the defects interact with the ions that shuffle in and out of the battery, a process known as ionic diffusion—a key mechanism for energy delivery. Singer also highlighted that the orientation of the dislocations shows that particle shape is important in the process; therefore, he and his colleagues intend to study whether this morphology can be adjusted to either facilitate or eliminate the dislocations.

We have yet to understand the role of extended defects in battery materials. For centuries, blacksmiths used defect engineering in metals to create stronger and more durable materials without even realizing it. Applying a defect-engineering approach to ceramics is much more challenging due to the presence of electrostatic charges. Nevertheless, with the help of new operando measurements and a better understanding of the mechanisms involved, we can now begin to address this challenge.

Andrej Singer, Assistant Professor, Department of Materials Science and Engineering, Cornell University

Stephanie Matson ‘20, M.S. ‘21, Daniel Weinstock, M.S. ‘21, Ziyi Wang, M.S. ‘19, and investigators from the University of California, San Diego, the University of Chicago, and Argonne National Laboratory are among the co-authors.

The National Science Foundation funded the study.

Journal Reference:

Gorobtsov, O., et al. (2023). Operando Interaction and Transformation of Metastable Defects in Layered Oxides for Na‐Ion Batteries. Advanced Energy Materials. doi.org/10.1002/aenm.202203654.

Source: https://www.cornell.edu/

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