Online ISSN : 2186-2451
Print ISSN : 1344-3542
ISSN-L : 1344-3542
High-Pressure Synthesis of Cation-Disordered Rock-Salt Oxyfluorides with High Crystallinity
Takeshi UYAMAKazuhiko MUKAIIkuya YAMADA
ジャーナル オープンアクセス

2021 年 89 巻 2 号 p. 94-99


Lithium-excess transition metal (M) oxyfluorides, LixMO1+xyFy, have received considerable attention as positive electrode materials for lithium-ion batteries. Little is known about the relationship between the crystallinity and electrochemical reactivities although this offers further understanding and improvement of LixMO1+xyFy, because conventionally ball-milled LixMO1+xyFy exhibits limited crystallinity, i.e., amorphous-like nanoparticles. We herein adapted a high-pressure/high-temperature method at 12 GPa and 1000 °C to synthesize high-crystallinity LixMO1+xyFy (M = Fe, Mn, V, Nb, Mo, and W) and investigated the electrochemical properties of this series. Rietveld analyses based on X-ray diffraction (XRD) and cross-sectional elemental mapping clarified that Li3VO3F and Li4WO4F crystalized as an almost-single-phase rock-salt structure with homogenous cation/anion distributions and formed well-faceted particles with sizes of 1–20 µm. Their rechargeable capacities over 1.8–5.0 V vs. Li+/Li were ∼40 mAh g−1 and ∼10 mAh g−1, respectively. According to ex situ XRD measurements of the cycled Li3VO3F electrodes, these partial rechargeable capacities were caused by a decomposition reaction during the initial charge, which differed from the topotactic reaction proposed for the low-crystallinity phases. This information is helpful for designing the microstructure of LixMO1+xyFy to improve its performance now that both crystal and amorphous LixMO1+xyFy phases are attainable.

© The Author(s) 2020. Published by ECSJ.

This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 License (CC BY, http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse of the work in any medium provided the original work is properly cited. [DOI: 10.5796/electrochemistry.20-65130].
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