A Two-Step Surface Modification Optimization for Performance Recovery of NaNi0.33Fe0.33Mn0.33O₂

Due to its excellent electrochemical performance, O3-type NaNi 0.33 Fe 0.33 Mn 0.33 O 2 (NFM) is one of the most promising cathode materials for sodium ion. However, its poor air stability has limited the industrialization process. In this work, a low-temperature two-step method which included carbon doping and acid treatment was used to improve the electrochemical property of the air-aged NaNi 0.33 Fe 0.33 Mn 0.33 O 2. X-ray diffraction results indicated that the structure of modified NFM (NFM-M) has good crystal structure stability. NFM-M, NFM-48H (NFM after air ageing of 48 h) and fresh NFM possessed a discharge capacity of 95.25, 74.92, and 100.79 mAh·g −1 in the first cycle, respectively. The modified sample exhibits outstanding cycling stability, with a capacity retention of 90.15% after 100 cycles at 0.1 C rate. Moreover, the NFM-M sample delivers excellent rate capability with improved capacity retention of 66.9% at 2.0 C rate.