Advanced characterizations play critical roles in understanding the fundamental properties of important materials. For accurate characterization, it is always necessary to address the possibility of probe-induced damage. A typical example is the successful application of cryo electron microscopy with low dose electron to characterize highly sensitive samples (ref1-3). Unfortunately, there have been very few studies on the effects of radiation damage on Li-ion battery systems caused by synchrotron x-ray beam. In this presentation, we provide direct evidence of synchrotron x-ray beam damage during in situ characterization of battery materials, observed by transmission x-ray microscopy (TXM). The unique capabilities of this technique in obtaining both morphological and chemical information enabled us to study the beam damage issue caused by x-ray. Li-rich Li_1.2Ni_0.13Mn_0.54Co_0.13O₂ material was characterized in situ to study the redox reaction mechanism of this material. Beam damage in the form of bubble formation in the liquid electrolyte was observed when the material was irradiated with x-ray during 2D/3D XANES (x-ray absorption near edge structure) image collection at Ni K-edge. The bubble formation in liquid electrolyte is most likely due to the decomposition of the electrolyte triggered by x-ray irradiation. This suggests beam damage issue needs to be considered not only for TXM which is commonly used to study the depth-dependent redox reaction in individual particles, but also spectroscopic techniques that employ similar energy range. Such damage may be related to the huge x-ray flux used in the in situ experiment. When filters were used to reduce the flux, the bubble formation was significantly reduced. We further show the evolution of the Ni redox during the cycling with suppressed beam damage, which should be more faithfully reflecting the situation.

Acknowledgement

This work was supported by the Assistant Secretary for Energy Efficiency and Renewable Energy, Vehicle Technology Office of the US Department of Energy (DOE) through the Advanced Battery Materials Research (BMR) Program, including Battery500 Consortium under contract no. DE-SC0012704. This research used beamline 18-ID of the National Synchrotron Light Source II, a US DOE Office of Science user facility operated for the DOE Office of Science by Brookhaven National Laboratory under contract no. DE-SC0012704.

References

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3. X. Wang et al., Nano Lett., 17, 7606–7612 (2017).