Decreasing transition metal triggered oxygen redox activity in Na-deficient oxides

How to utilize oxygen redox chemistry in oxide electrodes is a promising challenge to realize high-capacity cathodes. Herein, we demonstrate an unexpected strategy, ‘decreasing transition metal (TM)’ to form TM deficiency, to activate non-bonding O 2p orbitals in charge compensation process for the A-deficient (A: alkali metal, e.g., Li, Na) oxide electrodes. Na0.653Mn0.929O2, as a model material, has been successfully prepared and shows an obvious voltage plateau at ~ 4.2 V, corresponding to the oxygen redox (O2-/(O2)n-) with a total capacity of ~ 210 mAh g−1. This proposed strategy reveals that the special structural and chemical features can effectively increase O 2p orbitals near the Fermi level, triggering oxygen oxidation prior to transition metal oxidation towards a high-valence state. Our results provide an insightful guide for the further development of high-capacity materials, particularly for Na-deficient NaxTMO2 (x≤1) electrodes in Na-ion batteries (NIBs).