Thermal Stability of NaxCrO2 for Rechargeable Sodium Batteries; Studies by High-Temperature Synchrotron X-ray Diffraction

Naoaki Yabuuchi; Issei Ikeuchi; Kei Kubota; Shinichi Komaba

doi:10.1021/acsami.6b09280

Thermal Stability of Na_xCrO₂ for Rechargeable Sodium Batteries; Studies by High-Temperature Synchrotron X-ray Diffraction

ACS Appl Mater Interfaces. 2016 Nov 30;8(47):32292-32299. doi: 10.1021/acsami.6b09280. Epub 2016 Nov 17.

Authors

Naoaki Yabuuchi^{1

2

3}, Issei Ikeuchi¹, Kei Kubota^{1

2}, Shinichi Komaba^{1

2}

Affiliations

¹ Department of Applied Chemistry, Tokyo University of Science , 1-3 Kagurazaka, Shinjuku, Tokyo162-8601, Japan.
² Elements Strategy Initiative for Catalysts and Batteries (ESICB), Kyoto University , Katsura, Kyoto615-8510, Japan.
³ Department of Green and Sustainable Chemistry, Tokyo Denki University , 5 Senju Asahi-Cho, Adachi, Tokyo120-8551, Japan.

PMID: 27933819
DOI: 10.1021/acsami.6b09280

Abstract

Thermal stability and phase transition processes of NaCrO₂ and Na_0.5CrO₂ are carefully examined by high-temperature synchrotron X-ray diffraction method. O3-type NaCrO₂ shows anisotropic thermal expansion on heating, which is a common character as layered materials, without phase transition in the temperature range of 27-527 °C. In contrast, for the desodiated phase, in-plane distorted P3-type layered oxide (P'3 Na_0.5CrO₂), phase transition occurs in the following order. Monoclinic distortion associated with Na/vacancy ordering is gradually lost on heating, and its symmetry increases and changes to a rhombohedral lattice at 207 °C. On further heating, phase segregation to two P3 layered metastable phases, which have different interlayer distances (17.0 and 13.5 Å, presumably sodium-rich and sodium-free P3 phases, respectively) are observed on heating to 287-477 °C, but oxygen loss is not observed. Oxygen loss is observed at temperatures only above 500 °C, resulting in the formation of corundum-type Cr₂O₃ and O3 NaCrO₂ as thermodynamically stable phases. From these results, possibility of Na_xCrO₂ as a positive electrode material for safe rechargeable sodium batteries is also discussed.

Keywords: chromium oxide; high-temperature X-ray diffraction; phase transition; sodium battery; thermal stability.