title: Thermal Stability of NaxCrO2for Rechargeable Sodium Batteries; Studies by High-Temperature Synchrotron X-ray Diffraction.
abstract: Thermal stability and phase transition processes of NaCrO2and Na0.5CrO2are carefully examined by high-temperature synchrotron X-ray diffraction method. O3-type NaCrO2shows 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 Na0.5CrO2), 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 Cr2O3and O3 NaCrO2as thermodynamically stable phases. From these results, possibility of NaxCrO2as a positive electrode material for safe rechargeable sodium batteries is also discussed.
authors.affiliation: Department of Applied Chemistry, Tokyo University of Science , 1-3 Kagurazaka, Shinjuku, Tokyo162-8601, Japan.|Elements Strategy Initiative for Catalysts and Batteries (ESICB), Kyoto University , Katsura, Kyoto615-8510, Japan.|Department of Green and Sustainable Chemistry, Tokyo Denki University , 5 Senju Asahi-Cho, Adachi, Tokyo120-8551, Japan.
authors.forename: Naoaki
authors.initials: N
authors.lastname: Yabuuchi
authors.affiliation: Department of Applied Chemistry, Tokyo University of Science , 1-3 Kagurazaka, Shinjuku, Tokyo162-8601, Japan.
authors.forename: Issei
authors.initials: I
authors.lastname: Ikeuchi
authors.affiliation: Department of Applied Chemistry, Tokyo University of Science , 1-3 Kagurazaka, Shinjuku, Tokyo162-8601, Japan.|Elements Strategy Initiative for Catalysts and Batteries (ESICB), Kyoto University , Katsura, Kyoto615-8510, Japan.
authors.forename: Kei
authors.initials: K
authors.lastname: Kubota
authors.affiliation: Department of Applied Chemistry, Tokyo University of Science , 1-3 Kagurazaka, Shinjuku, Tokyo162-8601, Japan.|Elements Strategy Initiative for Catalysts and Batteries (ESICB), Kyoto University , Katsura, Kyoto615-8510, Japan.
authors.forename: Shinichi
authors.initials: S
authors.lastname: Komaba
keywords: chromium oxide; high-temperature X-ray diffraction; phase transition; sodium battery; thermal stability