Objective To solve the problems of P2-type Na_0.72Fe_0.3Mn_0.7O₂ cathode materials, such as easy occurrence of Jahn-Teller distortion, unstable crystal structure, slow Na⁺ transport rate and poor electronic conductivity during charge-discharge processes, Cu/Al co-doped P2-type Na_0.72Fe_0.15Cu_0.15Mn_0.65Al_0.05O₂ cathode materials were prepared by a high-temperature solid-state method.

Method The crystal structure and micromorphology of the materials were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Meanwhile, the electrochemical properties were systematically studied by combining galvanostatic charge-discharge and electrochemical impedance spectroscopy (EIS) tests.

Result The results indicate that Cu/Al co-doping does not alter the P2-type layered structure of the material, but also effectively promote particle growth and improves the particle dispersion. The introduction of Al³⁺ can substitute for part of Mn³⁺, thereby suppressing Jahn-Teller distortion, strengthening the Al-O covalent bond to stabilize the layered framework, and expanding the Na⁺ diffusion channels at the same time. Cu²⁺ doping can optimize the valence balance of the transition metal layer, inhibit irreversible phase transitions such as P2→O2, and enhance the intrinsic electronic conductivity of the material. Electrochemical test results show that in the voltage range of 2.0～4.25 V at 0.1C rate, the co-doped sample achieves an initial discharge specific capacity of 133.8 mAh/g, with a capacity retention rate of 93.01% after 50 cycles, which is significantly higher than that of the undoped sample (78.75%). The co-doped sample still maintains a discharge specific capacity of 55.2 mAh/g at a high rate of 10C, showing excellent rate performance. In addition, the charge-transfer impedance of the co-doped sample is significantly reduced, the Na⁺ diffusion coefficient is increased to 2.56×10⁻⁹ cm²/s, and the polarization phenomenon is obviously mitigated.

Conclusion This study confirms that Cu/Al co-doping can synchronously improve the structural stability and electrochemical kinetics, providing a feasible approach for the design and modification of high-performance layered oxide cathode materials for sodium-ion batteries.