Tailoring Anionic Redox Activity in a P2-Type Sodium Layered Oxide Cathode via Cu Substitution

Na-ion cathode materials cycling at high voltages with long cycling life and high capacity are of imminent need for developing future high-energy Na-ion batteries. However, the irreversible anionic redox activity of Na-ion layered cathode materials results in structural distortion and poor capacity retention upon cycling. Herein, we develop a facile doping strategy by incorporating copper into the layered cathode material lattice to relieve the irreversible oxygen oxidation at high voltages. On the basis of a comprehensive comparison with the Cu-free material, both the over-oxidation of O^2- to trapped molecular O₂ and Mn-related Jahn-Teller distortion have been effectively inhibited by restraining both the oxygen activity and participation of Mn⁴⁺/Mn³⁺ redox activity. Not limited to discovering stable cycling behavior at high voltages after Cu substitution, our findings also highlight an effective strategy to stabilize the anionic redox activity and elucidate the stabilization mechanism of Cu substitution, thus paving the way for further improvement of layered oxide cathode materials for high-energy Na-ion batteries.