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Nanosize Cation‐Disordered Rocksalt Oxides: Na 2 TiO 3 –NaMnO 2 Binary System
Author(s) -
Kobayashi Tokio,
Zhao Wenwen,
Rajendra Hongahally Basappa,
Yamanaka Keisuke,
Ohta Toshiaki,
Yabuuchi Naoaki
Publication year - 2020
Publication title -
small
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.785
H-Index - 236
eISSN - 1613-6829
pISSN - 1613-6810
DOI - 10.1002/smll.201902462
Subject(s) - redox , electrochemistry , materials science , electrode , cationic polymerization , inorganic chemistry , sodium , ion , chemical engineering , chemistry , polymer chemistry , metallurgy , organic chemistry , engineering
To realize the development of rechargeable sodium batteries, new positive electrode materials without less abundant elements are explored. Enrichment of sodium contents in host structures is required to increase the theoretical capacity as electrode materials, and therefore Na‐excess compounds are systematically examined in a binary system of Na 2 TiO 3 –NaMnO 2 . After several trials, synthesis of Na‐excess compounds with a cation disordered rocksalt structure is successful by adapting a mechanical milling method. Among the tested electrode materials, Na 1.14 Mn 0.57 Ti 0.29 O 2 in this binary system delivers a large reversible capacity of ≈200 mA h g −1 , originating from reversible redox reactions of cationic Mn 3+ /Mn 4+ and anionic O 2− /O n − redox confirmed by X‐ray absorption spectroscopy. Holes in oxygen 2p orbitals, which are formed by electrochemical oxidation, are energetically stabilized by electron donation from Mn ions. Moreover, reversibility of anionic redox is significantly improved compared with a former study on a binary system of Na 3 NbO 3 –NaMnO 2 tested as model electrode materials.