As a significant branch of cathodes for sodium-ion batteries (SIBs), the O3-type layered oxide usually receives extensive attention due to its high theoretical capacity. Due to the high tetrahedral site energy of Na+ diffusion transition state, the kinetics of the charge and discharge processes is sluggish. When the concentration of Na+ decreases, the transition metal layers undergo relative slip, leading to layer structure rearrangement and interface degradation, which result in a decrease in performance. In this work, we propose a strategy to optimize the above problem by varying the sodium content to prepare biphasic cathode materials. The prepared Na0.85Fe0.22Ni0.33Mn0.45O2 cathode has an O3/P2 biphasic structure. It shows excellent electrochemical performance, with an initial discharge specific capacity of 121.3 mAh g–1 at 0.1 C and a capacity retention rate of 94.9% after 100 cycles at 0.2 C. A small amount of P2 is introduced into the phase structure of the O3 to improve the diffusion kinetics and enhance the cycling stability. Due to the cooperative effect of O3/P2, the phase transition of O3/P2–O3/P3/P2 occurs in the electrochemical process, and the complex phase transition of O3–O’3 is inhibited. This study provides an idea for the preparation of high-performance cathode materials.
Shao-hua Luo,Ge Wang,Guodong Hao,Xinru Tian,Liu Yang,Sheng-xue Yan
Na x Ni 1/3 Fe 1/3 Mn 1/3 O 2 cathode material with high stability and high capacity is favored by researchers. However, during the charge-discharge process, Na x Ni 1/3 Fe 1/3 Mn 1/3 O 2 undergoes a series of complex phase transitions, which lead to the attenuation of its electrochemical performance and severely limit its application. In this paper, a series of Na x Ni 1/3 Fe 1/3 Mn 1/3 O 2 (0.6 ≤ x ≤ 1.0) cathode materials are synthesized by the high-temperature solid-state method, and the influence of varying sodium contents on the structure, Na occupancy, and various performance of the materials is analyzed. The results indicate that all four samples are P2 phase. However, they have different sodium sites (directly under the transition metal element (Na f ) and directly under the gap of the three transition metal elements (Na e )) occupancy. It is found that the Na f to Na e ratio of Na 0.9 Ni 1/3 Fe 1/3 Mn 1/3 O 2 material is 0.55, at which time Na f /Na e is lower and the electrochemical performance is the best. Its initial discharge specific capacity is 112mAg −1 , and after the multiplicative performance test, the discharge specific capacity is 95.7mAg −1 . The study shows that by adjusting the initial sodium content, the occupancy rate of different sodium sites is changed, which significantly affects the morphology, capacity, and cycling stability of the material.
危险品化学品经营许可证（带存储）