β‑Na_1.7IrO₃: A Tridimensional Na-Ion Insertion Material with a Redox Active Oxygen Network

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-Na_1.7IrO₃ 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-Na_1.7IrO₃ 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-Na_1.7IrO₃ 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

β‑Na_1.7IrO₃: A Tridimensional Na-Ion Insertion Material with a Redox Active Oxygen Network

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-Na_1.7IrO₃ 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-Na_1.7IrO₃ 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-Na_1.7IrO₃ 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

AVPO₄F (A = Li, K): A 4 V Cathode Material for High-Power Rechargeable Batteries

AVPO₄F (A = Li, K): A 4 V Cathode Material for High-Power Rechargeable Batterie