Synergistic Integration of P2/O3 Phases for Developing High‐Performance Sodium‐Ion Battery Cathodes

P2‐type Na 0.67 Ni 0.33 Mn 0.67 O 2 cathode, prominent for its high Na‐ion diffusion kinetics and rate performance, suffers from limited first charge capacity due to its deficient sodium content ( x = 0.67) and structural instability associated with P2–O2 phase transitions and Na + /vacancy ordering. In this study, the incorporation of Li + and Mg 2+ dual dopants into the lattice sites enhanced the sodium content through effective charge balancing thereby mitigating Na + /vacancy issues. Li doping contributed to stabilizing the Na + distribution while Mg 2+ promoted cationic ordering and suppressed undesirable phase transitions, collectively improving the structural integrity. The resulting layered cathode Na 0.85 Ni 0.32 Mn 0.60 Mg 0.03 Li 0.05 O 2 exhibited a biphasic P2/O3 structure, leveraging the synergistic benefits of both phases for improved electrochemical performance. In‐operando X‐ray diffraction and electrochemical analysis revealed that the material maintained structural integrity during cycling, while phase transition was significantly suppressed. The dual‐doped cathode delivered a capacity retention of 89% after 150 cycles at 1C, with a smoother voltage profile indicative of suppressed phase transitions. This work highlighted the effectiveness of Li–Mg dual‐doping strategy in optimizing the performance and stability of layered oxides, offering a pathway for high‐performance sodium‐ion batteries.