Preparation Technology And Electrochemical Behavior Of Na_0.44MnO₂ As Cathode Material For Sodium Ion Batteries

Due to the shortage of lithium resources, sodium ion batteries have attracted much attention in recent years. Sodium ion batteries are now actively studied, because of the potential advantages of low cost and widespread availability of sodium resources. The research of cathode materials is an important aspect of sodium ion batter ies development, especially Na_0.44MnO₂ with unique three dimensional tunnel structures, which can promote the migration of Na+. In this thesis, Na_0.44MnO₂ materials are prepared by different sintering temperature, sintering time, n（Na）/n（Mn） ratio and doping amount of cation. And the influences of above factors on Na_0.44MnO₂ materials are also indicated. The structure and morphology are characterized by X–ray Diffraction（XRD） and Scanning Electron Microscope（SEM）. The electrochemical properties are investigated by cyclic voltammetry（CV） and electrochemical impedance spectroscopy（EIS）.The main research results in this thesis are listed as follows:（1） For solid state method, one well-crystallized Na_0.44MnO₂ particles with moderate size are synthes ized at 800℃, which process high discharge capacity, stable cycle performance and rate performance. Impurities are produced in Na_0.44MnO₂ under too high or too low temperature, which impair the electrochemical properties of material.（2） The uniform particles are synthes ized during appropriate sintering time under certain sintering temperature. The capacity of material increases first and then decreases. With the sintering time increasing, the cycle stability has a good improvement.（3） Pure phase Na_0.44MnO₂ particles are prepared under appropriate n（Na）/n（Mn） ratio, and results show that Na_0.44MnO₂ with better electrochemical properties are synthes ized when n（Na）/n（Mn） ratio is 0.50. When n（Na）/n（Mn） ratio is below 0.48, Mn2O3 impurities are produced which impair the capacity and cycle stability.（4） The doping of Fe³⁺ change the reaction pattern. Under suitable doping ratio, the cycle stability improves, yet the specific capacity of material reduces. The electrochemical properties of material decline if the doping ratio beyond certain range. The doping of Fe3+ change the morphology, and the Na_0.44MnO₂ particle exhibites a structure of wide and thin flat plate via Fe3+ doping, which shorten the sodium ion diffusion paths effectively and promote the diffusion of the sodium ions.（5） After Li doping, there are two kinds of material with the morphology of rod-shaped and ball-shaped. The doping of Li also change the reaction pattern. The doping of Li improves cycle stability, but the charge and discharge specific capacity of material reduces. Li-doped improves the rate performance of Na_0.44MnO₂.