Thermal Expansion in Layered NaxMO2

• Published in: Scientific reports Vol. 8; no. 8; p. 3988
• Main Authors: 小林 航, 守友 浩, Kobayashi Wataru, Yanagita Ayumu, Akaba Takahiro, Shimono Takahiro, Tanabe Daiki, Moritomo Yutaka
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group 05.03.2018; Nature Publishing Group UK
• Subjects: 639/301/119/1002; 639/301/299/891; Humanities and Social Sciences; multidisciplinary; Science; Science (multidisciplinary)
• ISSN: 2045-2322; 2045-2322
• DOI: 10.1038/s41598-018-22279-9

Layered oxide Na x MO2 (M: transition metal) is a promising cathode material for sodium-ion secondary battery. Crystal structure of O3- and P2-type Na x MO2 with various M against temperature (T) was systematically investigated by synchrotron x-ray diffraction mainly focusing on the T-dependences of a- and c-axis lattice constants (a and c) and z coordinate (z) of oxygen. Using a hard-sphere model with minimum Madelung energy, we confirmed that c/a and z values in O3-type Na x MO2 were reproduced. We further evaluated the thermal expansion coefficients (α a and α c ) along a- and c-axis at 300 K. The anisotropy of the thermal expansion was quantitatively reproduced without adjustable parameters for O3-type Na x MO2. Deviations of z from the model for P2-type Na x MO2 are ascribed to Na vacancies characteristic to the structure.