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Published July 7, 2020 | Supplemental Material
Journal Article Open

Understanding the role of crystallographic shear on the electrochemical behavior of niobium oxyfluorides

Abstract

The effects of shear planes in perovskite materials have been studied in order to identify their role in the electrochemical behavior of Li⁺ intercalation hosts. These planes modulate the structural stability and ionic transport pathways and therefore play an intimate role in the characteristics and performance of shear compounds. Herein, two Nb-based compounds, NbO₂F and Nb₃O₇F, were chosen as representative perovskite and shear derivatives respectively to investigate the role of crystallographic shear. A series of operando measurements, including X-ray diffraction and X-ray absorption spectroscopy, in conjunction with structural analysis, Raman spectroscopy, and detailed electrochemical studies identified the effect of shear planes. It was found that shear planes led to increased structural stability during Li⁺ (de)intercalation with shear layers being maintained, while perovskite layers were seen to degrade rapidly. However, disordering in the shear plane stacking introduced during delithiation ultimately led to poor capacity retention despite structural maintenance as Li⁺ diffusion channels are disrupted.

Additional Information

© 2020 The Royal Society of Chemistry. Received 5th February 2020; Accepted 1st June 2020; First published 02 Jun 2020. This work was supported as part of the Center for Synthetic Control Across Length-scales for Advancing Rechargeables (SCALAR), an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences under award no. DE-SC0019381. Use of the Advanced Photon Source at Argonne National Laboratory was supported by the U. S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under contract no. DE-AC02-06CH11357. Use of shared facilities of the UC Santa Barbara Materials Research Science and Engineering Center (MRSEC, NSF DMR 1720256), a member of the Materials Research Facilities Network (http://www.mrfn.org), is gratefully acknowledged. J. J. Z. acknowledges support from the National Science Foundation Graduate Research Fellowship under grant no. (DGE-1745301). The authors thank Kamila M. Wiaderek and Sungsik Lee for useful discussions and advice regarding the X-ray Absorption Spectroscopy experiments. The authors declare no conflicts of interest.

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