Study On The Synthesis Of Spinel Lithium Manganate Cathode Materials And Ions-doped Modification

Spinel LiMn2O4 cathode material had drawn many researchers' attention due to the environmental protection,abundant sources,low cost,and good performance.However,the disadvantages including the low diffusion coefficients of Li+,poor electronic conductivity and bad cycling performances,thus the industrial field and market were limited.In order to improve the performances of the material,in this paper,the anion-cation compound substitution of cathod materials were synthesise by hydrothermal method and high temperature solid state method.It gave technical advieces in expanding the application of materials.1.The spherical MnO2 was synthesized by hydrothermal method.Using MnO2 as the precursor,then the Li Mn2O4 sample was prepared by two-step sintering method.The effects of temperature and Li/Mn on the microstructure,crystal structure and electrochemical performances was studyed,showing that the optimum reaction conditions was heating at 500? for 6 h,and then calcined at 750? for 18 h.2.The hydrothermal method was used to synthesize spherical MnO2 precursor which was assembled by tiny rods,then the LiMn2O4 spheres and LiFe0.08Mn1.92O3.84F0.16 spheres were synthesized by two-step sintering process.The morphologies of MnO2 were studied by SEM.Li Mn2O4 and LiFe0.08Mn1.92O3.84F0.16 samples were characterized by SEM,XRD,CV and charge-discharge tests.The results showed that Fe,F co-doping lithium manganese oxide had a regular morphology,a more stable crystal structure,better cycle and rate performance.The initial discharge capacity of LiFe0.06Mn1.94O3.88F0.12 was 133.6 m Ah/g at 0.2 C rate with better electrochemical performances and the capacity of LiMn2O4 was 128.8mAh/g respectively.The LiFe0.06Mn1.94O3.88F0.12 sample delivered a good initial discharge capacity of 121.6 mAh/g at 0.5 C and the capacity retention was 83.06%after 80 cycles,whereas the initial discharge capacity of LiMn2O4 was only 117.7mAh/g and the capacity retention was 77.57% respectively after 80 cycles.3.The nanometer spherical MnO2 was synthesized by hydrothermal method and used as precursor.And then spherical LiMn2O4,LiFe0.06Mn1.94O4 and LiNa0.06Mn1.94Fe0.06O4 were synthesized by 2-step sintering method.XRD,SEM,XPS and EDS were used to measure their physical characterizations,and EIS,CV and charge/discharge test were used to study their chemical performances.The results indicated that LiNa0.06Mn1.94Fe0.06O4 had stable crystal structure and smaller particles(about 160 nm),and it had better cycling performance and rate performance.After100 cycles at 0.5 C rate,the discharge capacity of LiNa0.06Mn1.94Fe0.06O4 was 108.0mAh/g,while that of LiMn2O4 was only 92.2 mAh/g,and their capacity retaining rates were 90.91% and 74.12%,respectively.At 10 C rate,the discharge capacity of LiNa0.06Mn1.94Fe0.06O4 was 34.3 mAh/g more than that of Li Mn2O4.Further study showed that the composite doping of Na+ and Fe3+ had a positive effect on the Li+diffusion coefficient and charge transfer resistance of the material.4.The single and composite doping had been studyed.LiMn1.97Zn0.03O4 was the optimal Zn2+ single doped material.Compared with LiMn2O4,LiMn1.97Zn0.03O4 had better electrochemical performances,better electrochemical reversibility and more stable structure.The LiMn1.97Zn0.03O3.92F0.08 sample has outstanding cycling and rate performance and its Li+ diffusion coefficient was bigger than that of Li Mn2O4 and LiMn1.97Zn0.03O4.