Analytical Sciences

Raman Imaging Analysis of Local Crystal Structures in LiCoO₂ Thin Films Calcined at Different Temperatures

Kosuke HARA,* Taka-aki YANO,*,** Kota SUZUKI,* Masaaki HIRAYAMA,* Tomohiro HAYASHI,*,** Ryoji KANNO,* and Masahiko HARA*,**,***

*Department of Electronic Chemistry, Interdisciplinary Graduate School of Science and Engineering, Tokyo Institute of Technology, 4259 Nagatsuta, Midori, Yokohama, Kanagawa 226-8502, Japan
**RIKEN, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan
***Earth-Life Science Institute, Tokyo Institute of Technology, Meguro, Tokyo 152-8551, Japan

Local crystalline structures of LiCoO₂ nanothin film cathodes in a lithium ion battery have been spectroscopically elucidated through confocal Raman imaging analysis at high spatial resolution of several hundred nanometers. A significant difference in the crystalline structure is found between the nanometric thin films and bulk powders. Thermally induced local decomposition of LiCoO₂ into an impurity phase on the films has also been revealed along with the mechanism of the temperature-triggered decomposition process. Moreover, frequency-based Raman imaging enables us to locally probe spatial separation between stoichiometric (LiCoO₂) and non-stoichiometric (Li_1-xCoO₂, 0 < x < 1) crystal phases on the thin films. Such local crystalline analysis is a promising approach to provide new insights into the degradation mechanism of lithium-ion batteries, which would result in improving the performance of thin film-based lithium ion batteries.

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