title: Sodium and Manganese Stoichiometry of P2-Type Na2/3 MnO2.
abstract: To realize a reversible solid-state Mn(III/IV) redox couple in layered oxides, co-operative Jahn-Teller distortion (CJTD) of six-coordinate Mn(III) (t2g (3) -eg (1) ) is a key factor in terms of structural and physical properties. We develop a single-phase synthesis route for two polymorphs, namely distorted and undistorted P2-type Na2/3 MnO2 having different Mn stoichiometry, and investigate how the structural and stoichiometric difference influences electrochemical reaction. The distorted Na2/3 MnO2 delivers 216 mAh g(-1) as a 3 V class positive electrode, reaching 590 Wh (kg oxide)(-1) with excellent cycle stability in a non-aqueous Na cell and demonstrates better electrochemical behavior compared to undistorted Na2/3 MnO2 . Furthermore, reversible phase transitions correlated with CJTD are found upon (de)sodiation for distorted Na2/3 MnO2 , providing a new insight into utilization of the Mn(III/IV) redox couple for positive electrodes of Na-ion batteries.
authors.affiliation: Department of Applied Chemistry, Tokyo University of Science, Shinjuku, Tokyo, 162-8601, Japan.|Umicore Japan KK, 1-2-3 Kita-Aoyama, Minato-ku, Tokyo, 107-0061, Japan.
authors.forename: Shinichi
authors.initials: S
authors.lastname: Kumakura
authors.affiliation: Department of Applied Chemistry, Tokyo University of Science, Shinjuku, Tokyo, 162-8601, Japan.
authors.forename: Yoshiyuki
authors.initials: Y
authors.lastname: Tahara
authors.affiliation: Department of Applied Chemistry, Tokyo University of Science, Shinjuku, Tokyo, 162-8601, Japan.|Elements Strategy Initiative for Catalysts & Batteries (ESICB), Kyoto University, 1-30 Goryo-Ohara, Nishikyo-ku, Kyoto, 615-8245, Japan.
authors.forename: Kei
authors.initials: K
authors.lastname: Kubota
authors.affiliation: Department of Applied Chemistry, Tokyo University of Science, Shinjuku, Tokyo, 162-8601, Japan.
authors.forename: Kuniko
authors.initials: K
authors.lastname: Chihara
authors.affiliation: Department of Applied Chemistry, Tokyo University of Science, Shinjuku, Tokyo, 162-8601, Japan. komaba@rs.kagu.tus.ac.jp.|Elements Strategy Initiative for Catalysts & Batteries (ESICB), Kyoto University, 1-30 Goryo-Ohara, Nishikyo-ku, Kyoto, 615-8245, Japan. komaba@rs.kagu.tus.ac.jp.
authors.forename: Shinichi
authors.initials: S
authors.lastname: Komaba
keywords: Jahn-Teller distortion; layered compounds; polymorphism; positive electrode materials; sodium-ion batteries