Study on high cycle stability of Na0.67Ni0.33Mn0.67O2 cathode material with hexagonal plate morphology

Because of its stable crystal structure and high theoretical capacity of 173 mAh center dot g-1, P2-Na0.67Ni0.33Mn0.67O2 (NNM) has been the subject of extensive research in recent years. However, its use has been restricted because of its low operating voltage and low cycle stability. The degree of the effect of sodium source content, calcination temperature, and calcination time on the specific capacity of NNM was determined in this paper by constructing a set of orthogonal experiments with three factors and three levels. Additionally, the impact of three factors on the material's crystal structure, morphology, and electrochemical performance was investigated, and the ideal process parameters were ultimately determined to be as follows: 4.5 % excess sodium, 800 degrees C calcination temperature, and 19 h calcination time. The NNM material possesses good crystallinity, no element segregation on its surface, medium particle size, distinct particle boundaries, and pores under ideal circumstances. After 200 cycles, the discharge capacity was 110.38 mAh center dot g-1, with the initial capacity reaching 155.42 mAh center dot g-1 at 0.1 C. As the scanning speed increases, the battery's capacity source shifts slowly from diffusion control behavior to pseudocapacitance control behavior. This implies that at high scanning speeds, the electrolyte has no time to diffuse into the electrode's deep surface; instead, more sodium ion deimpingement and the electrode material's redox reaction take place directly on the surface.