Study Of Synthesis And Properties Of Cathode Material For Sodium-Ion Batteries

Sodium-ion batteries have the following characteristics of abundant resources, low cost, lower electrolyte decomposition potential and high safety. Therefore, sodium ion batteries have a bright application prospect.In this thesis studies, two kinds of cathode materials P2-Na2/3Ni1/3Mn2/3O2and O3-NaNi0.5Mn0.5O2were synthesized. The structure and morphology of the prepared samples were examined by X-ray diffraction (XRD) and scanning electron microscope (SEM), and the charge and discharge performance of materials was tested at both room temperature and elevated temperature of55℃.(1) The Na2/3Ni1/3Mn2/3O2material was synthesized by a solid-state reaction method using Na2CO3, NiO and MnO2as reactant materials. The reaction temperature was850℃for12h. There was a trace amount of impurity NiO in the product. Its particles showed a polygon layered structure. The first specific discharge capacity of the material was88.4mAh/g at0.1C, and the capacity retention rate after20cycles was98%. When the current rate was increased to IC, the specific discharge capacity was79.5mAh/g and the capacity retention rate was98.4%after20cycles.(2) Adjusting the composition of the Na2/3Ni1/3Mn2/3O2material, we synthesized the Na0.8Ni0.4Mn0.6O2material by the same solid-state reaction. The material had no impurity phase and its particle morphology was good. The discharge capacities of Na0.8Ni0.4Mn0.6O2materials were respectively92mAh/g and85.3mAh/g at0.1C and IC, capacity retention rates after20cycles were97.4%and97.5%, respectively. Compared with the material Nao.67Ni0.33Mn0.67O2, the electrochemical performance of Na0.8Ni0.4Mn0.6O2had been improved. Furthermore, at elevated temperature (55℃), the material also remained good electrochemical performance.(3) The material NaNi0.5Mn0.5O2was prepared by a solid-state reaction method and an acetate decomposition method respectively. The sample prepared by acetate decomposition method was better than the one by solid state reaction method in ingredient purity, particle morphology and electrochemical performance. The discharge capacity of samples was116.7mAh/g at0.5C. After30cycles, the capacity retention rate was94.8%. The discharge capacities at1C,2C and5C were110.1mAh/g,95.3mAh/g and73.8mAh/g, respectively. When the current rate was returned to0.1C again, the discharge specific capacity restored to124mAh/g.