Study On The Synthesis And Performance Of Cathode Materials For Sodium-ion Batteries

Compared with lithium,sodium is richer in resources and its price is cheaper.So sodium ion batteries and their electrode materials have become the focus of research in recent years.At present,one the most widely studied cathode materials is layered metal oxide NaxMnO2.Because the radius of sodium ion is much larger than that of lithium ion,the migration rate of sodium ion in charge and discharge process becomes slower and the cycle performance and rate performance of sodium ion battery are affected.An effective way to improve the performance of materials is to dope metal ions.P2-Na0.67Ni0.33Mn0.67O2 material has high specific capacity and its derivatives have attracted wide attention.In this study,Na0.7ZnxMnyO2(x=0.1,0.15,0.2),P2-Na0.67LixNiyMn0.67O2(x=0.05,0.08,0.1)and O3-Nao.9Li0.2Ni0.45Mn0.5O2 materials were prepared by high temperature solid state method,and the effects of doping ion ratio,calcination temperature and calcination time on the structure,morphology and electrochemical performance of the materials were studied.The research contents and results are as follows:(1)The Na0.7ZnxMnyO2 materials with different doping ratios of Zn2+ have good crystallinity,obvious lamellar structure and no obvious agglomeration of particles.In the 2.0～4.4 V voltage range,the first charge curve of the material has a plateau at 4.1 V.XPS results show that the valence state of Mn4+has not changed significantly,while the valence state of O2-has changed.The potential of oxidation peaks and reduction peaks in the cyclic voltammetry curve is consistent with that of the plateaus in charge and discharge curves.When x=0.15,the charge transfer impedance is the smallest and the electrochemical performance is the best.The first charge and discharge specific capacities are 192.0 and 158.1 mAh/g,respectively.The capacity retention rate is 64.5%after 60 cycles.(2)When calcination temperature is 850℃ and x=0.05,the characteristic diffraction peaks of Na0.67Li0.05Ni0.3Mn0.67O2 material are basically consistent with the standard spectra of Na0.67Ni0.33Mn0.67O2.The material is composed of lamellar with a certain thickness.In the range of 2.0～4.0 V voltage,the first charge and discharge specific capacities of the material are 92.0 and 90.4 mAh/g,respectively.After 60 cycles,the capacity retention rate is 95.1%.There are three pairs of oxidation and reduction peaks in the cyclic voltammetry curve,which correspond to different redox reactions.The charge transfer impedance of the material is 101Ω.(3)When calcination time is 12 h,the XRD pattern of Na0.9Li0.2Ni0.45Mn0.5O2 shows that the structure of the material is O3.The morphology is lamellar structure and the distribution of particle is uniform.In the range of 2.0～4.0 V voltage,the first charge and discharge specific capacities of the material are 118.3 and 121.5 mAh/g,respectively.After 60 cycles,the capacity of the material remains 90.9%.There are three pairs of obvious redox peaks in the cyclic voltammetry curve,which correspond to the electrochemical reactions of different elements.