Strengthening Transition Metal–Oxygen Interaction in Layered Oxide Cathodes for Stable Sodium-Ion Batteries

P2-type layered oxides, such as Na0.67Ni0.33Mn0.67O2, represent a promising class of cathode materials for Sodium-ion batteries (SIBs) due to their high theoretical energy density. However, their cycling stability is often compromised by severe phase transitions and irreversible lattice oxygen redox reactions at high voltages. In this work, we develop a Zn and Al codoping approach to design a Na0.71Ni0.28Zn0.05Mn0.62Al0.05O2 (ZA-NNMO) cathode for stable SIBs. Geometric phase analysis reveals that the introduction of inert Zn significantly mitigates the lattice distortion and transition-metal-ion migration, thereby inhibiting detrimental phase transition and structural collapse. The doped Al element in the Mn site strengthens the Al-O interaction, facilitating reversible O2--O2n- (0 < n < 4) reactions at high voltages and effectively curtailing irreversible lattice oxygen oxidation, as confirmed by in situ differential electrochemical mass spectrometry. As a result, the ZA-NNMO cathode delivers superior electrochemical performance in terms of high output voltage of 3.6 V, highly competitive energy density of 470 W h kg-1 and good cyclability (80.2% of capacity retention after 1400 cycles at 1.0 A g-1). This work presents a robust methodology for improving the reversibility and stability of layered oxide cathodes in SIBs.