Low-cost and robust iron-doped P2-type manganese oxide cathode for high-performance sodium ion batteries

P2-type Na 0.67 MnO 2 cathode material has attracted significant attention due to its high specific capacity, and abundant sodium resources for practical sodium-ion batteries (SIBs). However, the complex phase transitions of this material in the charge/discharge processes could lead to rapid voltage/capacity decay, limiting its practical applications. In this study, to suppress this phase transition, stabilize the structure, and regulate Mn ion activity, we use a sol-gel method to dope Fe ions into these materials by partially replacing Mn, resulting in a series of Fe-doped P2-type Na 0.67 MnO 2 cathode materials (Na 0.67 Mn (1- x /6) Fe x /6 O 2 ( x = 0, 1, 2, 3, 4). According to our theoretical calculations and experimental optimization experiments, the introduction of Fe ions could stabilize the material structure and reduce the energy barrier for Na + ion mass transport. As a result, the doped cathode materials ( x = 1, 2, 3, 4) exhibit significantly better performance than the pristine Na 0.67 MnO 2 cathode ( x = 0). Among the Fe-doped cathode materials (with x = 1, 2, 3, 4), Na 0.67 Mn 0.5 Fe 0.5 O 2 ( x = 3) delivers the best cycle performance, high-rate capability, and stability, e.g., discharge capacity of 114.7 mAh g −1 and 79.1 mAh g −1 at 1.0C and 5.0C respectively, and retains 91.1 % capacity after 200 cycles at 1.0C. This work provides both theoretical insights and practical strategies for designing and fabricating cathode materials for low-cost, robust, and high-performance SIBs. • Fe-doped P2-Na0.67MnO2 cathodes are synthesized via a low-cost sol-gel method. • DFT calculations reveals Fe 3+ doping suppresses Jahn-Teller distortion. • Na0.67Mn0.5Fe0.5O2 sample exhibits the smallest volume change (0.033 %). • Na0.67Mn0.5Fe0.5O2 sample achieves 91.1 % capacity retention (200 cycles, 1C).