β‑Na1.7IrO3: A Tridimensional Na-Ion Insertion Material with a Redox Active Oxygen Network

• Published in: Chemistry of materials Vol. 30; no. 10; pp. 3285 - 3293
• Main Authors: Pearce, Paul E, Rousse, Gwenaelle, Karakulina, Olesia M, Hadermann, Joke, Van Tendeloo, Gustaaf, Foix, Dominique, Fauth, François, Abakumov, Artem M, Tarascon, Jean-Marie
• Format: Journal Article
• Language: English
• Published: American Chemical Society 22-05-2018
• ISSN: 0897-4756; 1520-5002
• DOI: 10.1021/acs.chemmater.8b00320

The revival of the Na-ion battery concept has prompted an intense search for new high capacity Na-based positive electrodes. Recently, emphasis has been placed on manipulating Na-based layered compounds to trigger the participation of the anionic network. We further explored this direction and show the feasibility of achieving anionic-redox activity in three-dimensional Na-based compounds. A new 3D β-Na1.7IrO3 phase was synthesized in a two-step process, which involves first the electrochemical removal of Li from β-Li2IrO3 to produce β-IrO3, which is subsequently reduced by electrochemical Na insertion. We show that β-Na1.7IrO3 can reversibly uptake nearly 1.3 Na+ per formula unit through an uneven voltage profile characterized by the presence of four plateaus related to structural transitions. Surprisingly, the β-Na1.7IrO3 phase was found to be stable up to 600 °C, while it could not be directly synthesized via conventional synthetic methods. Although these Na-based iridate phases are of limited practical interest, they help to understand how introducing highly polarizable guest ions (Na+) into host rocksalt-derived oxide structures affects the anionic redox mechanism.