Cu-Occupied Ni-Site O3-Type Layered NaNi_0.5Mn_0.5O₂ with Enhanced Rate Performance for Sodium-ion Batteries

Layered O3-type oxides, as cathode materials for sodium-ion batteries, have attracted extensive attention due to its high working potential and high capacity value because of the large amount of sodium contained in their lattice. However, the complex phase transition usually causes the battery capacity to decay rapidly, especially the complex phase transition that occurs during the sodium insertion/extraction process, which is harmful to the structural stability, and this will seriously hinder its practical application. Therefore, we adopt the method of Cu element doping to improve the electrochemical performance of the layered transition metal oxide cathode of the O3-type sodium-ion battery. By doping Cu²⁺ to adjust the local chemical environment in O3-NaNi_0.5Mn_0.5O₂, thereby improving its electrochemical performance. We successfully prepared O3-NaNi_0.5Mn_0.5O₂ and Cu-doped cathode materials by the sol–gel method. Among them, the initial discharge capacity of NaNi_0.4Mn_0.5Cu_0.1O₂ at 0.1C is 110.4 mAh·g⁻¹, and the remaining capacity after 100 cycles at 0.1 C is 75.1 mAh·g⁻¹. When the electrode is recycled again at a rate of 0.1 C, the capacity of NC1 can be restored to 97.45 mAh·g⁻¹, indicating that it has excellent structural reversibility and excellent rate performance.