Erick Espinosa-Villatoro, SSRL

Abstract

Synchrotron X-ray Studies Reveal Extreme Fast Charging Effects on NMC811 Li-ion Battery Cathodes

E. Espinosa-Villatoro*, Molleigh B. Preefer and Johanna Nelson Weker*
Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, Menlo Park, California 94025, United States of America.

* erickleo@slac.stanford.edu, jlnelson@slac.stanford.edu

The development of lithium-ion batteries that can be charged in 15 minutes or less is critical because Extreme Fast Charging (XFC) is essential if electric vehicles are ever to compete with internal combustion vehicles [1]. In the last few years, the battery science community has made a great effort to identify the problems and to develop new strategies for the efficient and correct use of XFC [2]. Therefore, it is imperative to have a comprehensive understanding of the degradation processes that occur in battery components, such as the cathodes, when XFC is used. Previous research has revealed the preeminent aging mechanisms at several length scales, revealing electrochemical correlations in cathodes that are based on the LiNixMnyCozO2 (NMC) [3]. In this work, synchrotron radiation-based X-ray techniques such as X-ray transmission with near-edge structure X-ray absorption (TXM-XANES) analysis, micro X-ray fluorescence (μ-XRF), and micro X-ray absorption spectroscopy (μ-XAS) are used to study the degradation behavior of NMC811/graphite Li-ion cells after cycling under XFC conditions. The obtained results provide critical insight into the elemental distribution within NMC cathodes. To obtain this data, we harnessed the Ni K-edge energy in μ-XRF. At the same time, we used X-ray computed tomography (XCT) to study the internal component morphology of the Li-ion cells. In addition, guided by μ-XRF elemental maps multiple XANES analyses at different cathode spots to study the local changes depending on the states of charge (SoCs) were performed. Nevertheless, our μ-XRF-XANES results did not reveal any significant discrepancies, regardless of the specific cathode area examined. Therefore, an additional charge-discharge cycle was performed, and μ-CT was used to analyze the chemical behavior of the cells. It was found that the cells retained the ability to charge and discharge even after being subjected to multiple charge-discharge cycles under XFC conditions and stored for a long period of time. XANES analysis showed the changes in oxidation states as a function of SoC. It is important to note that for non-destructive in-situ analysis of battery materials during cycling (operando) and under XFC conditions, synchrotron radiation techniques provide high spatial resolution, sensitivity, and elemental specificity. By providing critical information on the microstructure and chemical composition of battery materials, X-ray techniques are essential for understanding and improving battery behavior and performance.

References
[1] Y. Lu, et al., Small, 18 (2022) 2105833.
[2] M. Preefer, et al., J. Phys. Chem. C, 126 (2022) 21196−21204.
[3] T. Tanim, et al., Adv. Energy Mater., 12 (2022) 2202795.