title: Intermediate honeycomb ordering to trigger oxygen redox chemistry in layered battery electrode.
abstract: Sodium-ion batteries are attractive energy storage media owing to the abundance of sodium, but the low capacities of available cathode materials make them impractical. Sodium-excess metal oxides Na2MO3 (M: transition metal) are appealing cathode materials that may realize large capacities through additional oxygen redox reaction. However, the general strategies for enhancing the capacity of Na2MO3 are poorly established. Here using two polymorphs of Na2RuO3, we demonstrate the critical role of honeycomb-type cation ordering in Na2MO3. Ordered Na2RuO3 with honeycomb-ordered [Na(1/3)Ru(2/3)]O2 slabs delivers a capacity of 180 mAh g(-1) (1.3-electron reaction), whereas disordered Na2RuO3 only delivers 135 mAh g(-1) (1.0-electron reaction). We clarify that the large extra capacity of ordered Na2RuO3 is enabled by a spontaneously ordered intermediate Na1RuO3 phase with ilmenite O1 structure, which induces frontier orbital reorganization to trigger the oxygen redox reaction, unveiling a general requisite for the stable oxygen redox reaction in high-capacity Na2MO3 cathodes.
authors.affiliation: Department of Chemical System Engineering, School of Engineering, The University of Tokyo, Hongo 7-3-1, Bunkyo-ku, Tokyo 113-8656, Japan.|Elements Strategy Initiative for Catalysts &Batteries (ESICB), Kyoto University, Nishikyo-ku, Kyoto 615-8245, Japan.
authors.forename: Benoit
authors.initials: B
authors.lastname: Mortemard de Boisse
authors.affiliation: Department of Chemical System Engineering, School of Engineering, The University of Tokyo, Hongo 7-3-1, Bunkyo-ku, Tokyo 113-8656, Japan.
authors.forename: Guandong
authors.initials: G
authors.lastname: Liu
authors.affiliation: Department of Chemical System Engineering, School of Engineering, The University of Tokyo, Hongo 7-3-1, Bunkyo-ku, Tokyo 113-8656, Japan.
authors.forename: Jiangtao
authors.initials: J
authors.lastname: Ma
authors.affiliation: Department of Chemical System Engineering, School of Engineering, The University of Tokyo, Hongo 7-3-1, Bunkyo-ku, Tokyo 113-8656, Japan.|Elements Strategy Initiative for Catalysts &Batteries (ESICB), Kyoto University, Nishikyo-ku, Kyoto 615-8245, Japan.
authors.forename: Shin-Ichi
authors.identifier: http://orcid.org/0000-0001-7464-8692
authors.initials: SI
authors.lastname: Nishimura
authors.affiliation: Department of Chemical System Engineering, School of Engineering, The University of Tokyo, Hongo 7-3-1, Bunkyo-ku, Tokyo 113-8656, Japan.|Elements Strategy Initiative for Catalysts &Batteries (ESICB), Kyoto University, Nishikyo-ku, Kyoto 615-8245, Japan.
authors.forename: Sai-Cheong
authors.initials: SC
authors.lastname: Chung
authors.affiliation: Department of Applied Chemistry, School of Engineering, The University of Tokyo, Bunkyo-ku, Tokyo 113-8656, Japan.
authors.forename: Hisao
authors.initials: H
authors.lastname: Kiuchi
authors.affiliation: Institute for Solid State Physics, The University of Tokyo, Kashiwa, Chiba 277-8581, Japan.|Synchrotron Radiation Research Organization, The University of Tokyo, Tatsuno, Hyogo 679-5165, Japan.
authors.forename: Yoshihisa
authors.initials: Y
authors.lastname: Harada
authors.affiliation: Advanced Key Technologies Division, National Institute for Materials Science, Tsukuba, Ibaraki 305-0044, Japan.
authors.forename: Jun
authors.initials: J
authors.lastname: Kikkawa
authors.affiliation: Department of Engineering Science, The University of Electro-Communications, Chofu, Tokyo 182-8585, Japan.|RIKEN Nishina Center for Accelerator-Based Science, RIKEN, Wako, Saitame 351-0198, Japan.
authors.forename: Yoshio
authors.initials: Y
authors.lastname: Kobayashi
authors.affiliation: Department of Chemical System Engineering, School of Engineering, The University of Tokyo, Hongo 7-3-1, Bunkyo-ku, Tokyo 113-8656, Japan.|Elements Strategy Initiative for Catalysts &Batteries (ESICB), Kyoto University, Nishikyo-ku, Kyoto 615-8245, Japan.
authors.forename: Masashi
authors.initials: M
authors.lastname: Okubo
authors.affiliation: Department of Chemical System Engineering, School of Engineering, The University of Tokyo, Hongo 7-3-1, Bunkyo-ku, Tokyo 113-8656, Japan.|Elements Strategy Initiative for Catalysts &Batteries (ESICB), Kyoto University, Nishikyo-ku, Kyoto 615-8245, Japan.
authors.forename: Atsuo
authors.initials: A
authors.lastname: Yamada