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成果報告書詳細
管理番号20190000000576
タイトル*2018年度中間年報 革新型蓄電池実用化促進基盤技術開発(国立大学法人東京大学)
公開日2019/6/15
報告書年度2018 - 2018
委託先名国立大学法人東京大学
プロジェクト番号P16001
部署名次世代電池・水素部
和文要約
英文要約Title: Research & Development Initiative for Scientific Innovation of New Generation Batteries 2 (RISING2); (FY2016-FY2018) FY2018 Annual Report

For the development of innovative rechargeable battery materials, it is essential to find a new pathway to reduce the resistances for ionic conductivity. The main resistances for ionic conductivity are due to the lattice defects such as grain boundary or hetero-interface between electrode and electrolyte materials. In additional, point defects including vacancies or dopants also affect the resistance for ionic conductivity. The purpose of this study is to develop 3D imaging, and local electric field imaging for characterizing innovative rechargeable battery materials by using scanning transmission electron microscopy (STEM) and related measurement methodologies.

(1) Development of 3D imaging
We have been installed and tuned up a newly developed Delta-type aberration corrector on ARM300CF at the University of Tokyo. It is now routinely available to use the illumination semi-angle of 63 mrad at 300 kV, which provides a higher depth resolution better than 3 nm. To directly demonstrate the potential of this microscope, we observed a solid-state electrolyte of (Li,La)TiO3 by optical depth sectioning. We then realized that it might be possible to directly determine La substitutional defects for Li-site in 3D.

(2) Charge density imaging by a segment detector
The mobility of anion or cation in solids are strongly affected by not only the atom configurations but also electric field or charge density distributions in materials. We have developed direct electric field imaging in STEM by using our custom-made segment-type detector. According to Maxwell equations, once we obtain electric field images, we can derive the charge density image, although it is necessarily to enhance signal-to-noise ratio of the electric field images. To observe charge density distribution in solid, we selected GaN [11-20] orientation and we have successfully determined the charge density distribution at atomic resolution (G. Sanchez-Santolino, ACS Nano (2018)). In detailed analysis, we realized that the negative contrasts at 0.6 Ångströn away from the Ga nucleus correspond to the electron clouds.


(3) Accurate electrochemical impedance analysis
Electrochemical impedance spectroscopy is the most popular measurement system to simultaneously evaluate an ionic conductivity at both the internal gain and the grain boundary. To determine the ionic conductivity, we need to fit the spectrum and usually gradient decent algorithm is adopted for the curve fitting. However, this algorithm is strongly affected by initial values, which may lead to local minima rather than the global minimum. To overcome this issue, we developed Metropolis-Hastings algorithm which successfully provides the global minimum, independent of initial values (K. Kawahara et al, J. Power Souses (2018)).
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