Regulating Phase Transition and Oxygen Redox to Achieve Stable High-Voltage O3-Type Cathode Materials for Sodium-Ion Batteries

O3-type layered oxides are promising cathode materials for sodium-ion batteries. However, unsatisfying cyclic stability hinders its practical application, mainly resulting from harmful phase transition and irreversible oxygen redox, especially in high-voltage regions. Herein, a co-doped strategy by incorporating Li + , Mg 2+ , Ca 2+ , and Sb 5+ into the O3-Na 0.8 Ni 0.4 Fe 0.2 Mn 0.4 O 2 cathode materials is proposed. Both suppressing the undesired phase transition over 4.1 V (vs Na/Na + ) and reducing the anisotropic strain are achieved with the novel Na 0.8 Ni 0.3 Fe 0.2 Mn 0.3 Li 0.1 Mg 0.02 Ca 0.05 Sb 0.03 O 2 (LMCS NFM). Moreover, restricted but highly reversible oxygen redox is observed due to strong attraction from Sb 5+ and special “Li–O-vacancy” and “Mg–O-vacancy” configurations. The strategy brings about excellent high-voltage cyclic stability with a reversible capacity of 130 mAh g −1 and a capacity retention of 85% after 250 cycles at 4.2 V, and less thermal runaway risk and moisture sensitivity, increasing the probability of O3-type oxide cathode practical applications.