Analytical Sciences

Abstract − Analytical Sciences, 33(7), 853 (2017).

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 (Li1-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.