| 研究課題/領域番号 |
22KF0245
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| 補助金の研究課題番号 |
22F22358 (2022)
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| 研究種目 |
特別研究員奨励費
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| 配分区分 | 基金 (2023)
補助金 (2022) |
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| 応募区分 | 外国 |
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| 審査区分 |
小区分28010:ナノ構造化学関連
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| 研究機関 | 大阪大学 |
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研究代表者 |
末永 和知 大阪大学, 産業科学研究所, 教授 (00357253)
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| 研究分担者 |
LIU QIUNAN 大阪大学, 産業科学研究所, 外国人特別研究員
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| 研究期間 (年度) |
2023-03-08 – 2025-03-31
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| 研究課題ステータス |
交付 (2023年度)
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| 配分額 *注記 |
2,300千円 (直接経費: 2,300千円)
2024年度: 700千円 (直接経費: 700千円)
2023年度: 1,100千円 (直接経費: 1,100千円)
2022年度: 500千円 (直接経費: 500千円)
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| キーワード | 2D materials / EELS / in situ TEM / battery / STEM / intercalation |
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| 研究開始時の研究の概要 |
二次バッテリーの電極材料として有望なグラファイトなど二次元材料であるが、その正確なインターカレーション構造はいまだに明らかになっていない。本研究では最先端の電子顕微鏡を用いて、各種イオンと電極材料の相互作用を直接観察することにより、その内包メカニズムを原子レベルで明らかにする。これにより各種アルカリ金属や新構造をもつ積層構造物質の構造変化を実時間で観察し、バッテリー経年劣化の原因となる構造変化を確かめる。これらの実験は将来のエネルギー研究に基礎的な知見を与えることになる。
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| 研究実績の概要 |
Our research focused on intercalation or doping of 2D materials combining electron microscopy with theory. We used advanced spherical aberration-corrected scanning transmission electron microscopy (STEM) to successfully identify the atomic structure of molybdenum chloride intercalated between two graphene layers. When we inserted MoCl5 between bilayer graphene, we revealed a myriad of nanostructures, such as networks (MoCl3), chains (MoCl2), and rings (Mo5Cl10), shedding light on the molybdenum chloride nanostructures. More interestingly, large distortions of the Mo bonds in combination with frequent structural transitions occur in the molybdenum chloride systems, which is consistent with the results of our first-principles calculations. This work has been just published in ACS Nano.
We also explored the doping process of various alkali metals in monolayer MoS2 using STEM coupled with electron energy loss spectroscopy (EELS). We successfully achieved phase transitions from the H-phase to the T-phase, T’-phase, and ultimately the T’’-phase by doping MoS2 with light alkali metals (Li, Na, and K). The Mo-L2,3 peaks in the EELS spectra exhibited a continuous redshift from the H phase to the T'' phase, indicating electron provision by the alkali metals and a reduction process of the Mo core oxidation state. Moreover, using heavier alkali metals Rb and cesium Cs as dopants, we successfully visualized their initial doping positions in the H phase via STEM. Rb doping induced the phase transition of MoS2 only to the T phase, while Cs doping did not induce any phase transition.
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| 現在までの達成度 (区分) |
現在までの達成度 (区分)
2: おおむね順調に進展している
理由
We declare that that our project has progressed smoothly as envisaged. The experimental results have even exceeded our expectations. For instance, when heavy alkali metals are doped into MoS2, it does not induce a significant phase transition but instead deposits as two layers of alkali metal on the surface of the H phase MoS2. This breaks the limitation that alkali metals must contribute electrons, providing guidance for the development of alkali metal ion batteries. Additionally, the intercalation of molybdenum chloride into bilayer graphene exhibits a structure completely different from the anticipated scenario. Our real structure characterization provides valuable reference for both theoretical and experimental studies, guiding the application of 2D-like electrode materials or other devices.
A more profound advancement lies in bilayer graphene, where when alkali metal Na encounters iron chloride, we successfully utilized the energy of electron beams to reduce FeCl3 to form the thinnest NaCl salt bilayer structure in bilayer graphene, a result previously unimaginable. Data analysis and theoretical calculations are currently being organized, and we look forward to the prompt publication of this exciting work.
Our experiments are ongoing, and we have successfully published some early papers. While, some related experimental results have been transferred to theoretical group, hoping to receive more support to further determine the specific evolution mechanism of the internal structure, deepening theoretical impressions and understanding of the research results obtained.
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| 今後の研究の推進方策 |
Plans for the final year of 2024 are as follows:
1 The project of various alkali metal doping on monolayer MoS2 is currently awaiting the computational results from the theoretical research group. Upon successful completion, the drafting process will commence, followed by submission to relevant journals for publication.
2 The experimental results and theoretical calculations concerning the phase structure and phase conversion of iron chloride intercalated in bilayer graphene have been integrated and are currently being compiled into a manuscript. We aim for a successful publication within this year.
3 Preliminary results regarding the chemical reaction between alkali metal Na and metal iron chloride atoms in bilayer graphene have been obtained. Subsequent research aims to further investigate the structural correlation between different alkali metals and metal chlorides in two-dimensional materials (bilayer graphene). We seek to explore potential applications and value of the relevant structures in various fields such as optics, electronics, and other devices, particularly assessing whether there may be unexpected enhancements in capacity and rate performance when applied in alkali metal ion batteries.
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