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Strong Oxygen Participation in the Redox Governing the Structural and Electrochemical Properties of Na-Rich Layered Oxide Na2 IrO3

Abstract : The recent revival of the Na-ion battery concept has prompted intense activities in the search for new Na-based layered oxide positive electrodes. The largest capacity to date was obtained for a Na-deficient layered oxide that relies on cationic redox processes only. To go beyond this limit, we decided to chemically manipulate these Na-based layered compounds in a way to trigger the participation of the anionic network. We herein report the electrochemical properties of a Na-rich phase Na2IrO3, which can reversibly cycle 1.5 Na+ per formula unit while not suffering from oxygen release nor cationic migrations. Such large capacities, as deduced by complementary XPS, X-ray/neutron diffraction and transmission electron microscopy measurements, arise from cumulative cationic and anionic redox processes occurring simultaneously at potentials as low as 2.7 V vs Na+/Na. The inability to remove more than 1.5 Na+ is rooted in the formation of an O1-type phase having highly stabilized Na sites as confirmed by DFT calculations, which could rationalize as well the competing metal/oxygen redox processes in Na2IrO3. This work will help to define the most fertile directions in the search for novel high energy Na-rich materials based on more sustainable elements than Ir.
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Submitted on : Wednesday, November 30, 2016 - 1:02:21 PM
Last modification on : Monday, May 10, 2021 - 3:36:01 PM
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Arnaud J. Perez, Dmitry Batuk, Matthieu Saubanère, Gwenaelle Rousse, Dominique Foix, et al.. Strong Oxygen Participation in the Redox Governing the Structural and Electrochemical Properties of Na-Rich Layered Oxide Na2 IrO3 . Chemistry of Materials, American Chemical Society, 2016, 28 (22), pp.8278 - 8288. ⟨10.1021/acs.chemmater.6b03338⟩. ⟨hal-01405732⟩

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