Electrochemical performance and structural stability of air-stable Na0.67Ni0.33Mn0.67-xTixO2 cathode materials for high-performance sodium-ion batteries

P2-type Na0.67Ni0.33Mn0.67O2 layered oxide has attracted the significant attention as the layered structure cathode material of sodium-ion battery owing to its high energy density. However, it exhibits unsatisfied cyclic stability and severe voltage decay in practical operation process. Herein, a series of P2-type Na0.67Ni0.33Mn0.67-xTixO2 (x = 0, 0.1, 0.2, 0.3) are prepared by a modified sol–gel method to mitigate this issue. It has been found that Ti substitution can expand the slab-spacing, suppress Na+/vacancy ordering and the P2 − O2 phase transition. Especially, the air-stable Na0.67Ni0.33Mn0.47Ti0.2O2 exhibits the enhanced rate capability (51.9 mAh g−1 at 10C) and excellent cycling stability (70.2% capacity retention after 200 cycles at 1C). Additionally, the Ti substitution can significantly prevent the particle of material from cracking when charged to a higher voltage. Moreover, it can repress the side reactions between the active material and the electrolyte at high voltage by reducing their contact area, and thus availably inhibiting the voltage decay during charge/discharge cyclic process. Accordingly, the Ti substitution strategy provides a simple and effective horizon for designing and developing the high energy density layered oxide cathode materials of sodium-ion batteries.