Strong oxygen participation in the redox governing the structural and electrochemical properties of Na-rich layered oxide Na2IrO3

Arnaud J. Perez, Dmitry Batuk, Matthieu Saubanère, Gwenaelle Rousse, Dominique Foix, Eric McCalla, Erik J. Berg, Romain Dugas, Karel H W Van Den Bos, Marie Liesse Doublet, Danielle Gonbeau, Artem M. Abakumov, Gustaaf Van Tendeloo, Jean Marie Tarascon

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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.

Original languageEnglish (US)
Pages (from-to)8278-8288
Number of pages11
JournalChemistry of Materials
Issue number22
StatePublished - Nov 22 2016

Bibliographical note

Funding Information:
Use of the 11-BM mail service of the APS at Argonne National Laboratory was supported by the U.S. department of Energy under contract No. DE-AC02-06CH11357 and is greatly acknowledged. D.B, G.R, and J.-M.T. acknowledge funding from the European Research Council (ERC) (FP/2014-2020)/ERC Grant-Project 670116-ARPEMA.

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