| In this paper,the metal vanadates Zn3V3O8,BiVO4/Fe VO4 and Ce VO4 are chosen as anode materials for study.The synthesis,modification and electrochemical properties for the above materials are studied and discussed.The Zn3V3O8 anode material is mainly modificated by compositing with Fe3O4and doping with Co2+,and the Ce VO4 anode material is modificated by compositing with Fe3O4.The electrochemical properties and reaction mechanism for both BiVO4/Fe VO4 and Ce VO4/Fe3O4 are discussed also.The important conclusions obtained are listed as follows:(1)The Zn3V3O8 micron flowers were synthesized by solvothermal method using Zn(NO3)3·6H2O and NH4VO3 as raw materials.The Zn3V3O8 was composited by Fe3O4 to form Zn3V3O8/Fe3O4 composite.In addition,Zn2.88Co0.12V3O8 was synthesized by solvothermal method using Co(NO3)2·6H2O to replace part of Zn(NO3)3·6H2O.The samples were characterized by X-ray diffraction and scanning electron microscopy.Electrochemical tests showed that the initial discharge specific capacity for Zn3V3O8/Fe3O4 nanoparticles was1431.8 m Ah·g-1 when the current density was 100 m A·g-1,which was much higher than that of both pure Zn3V3O8(563.5 m Ah·g-1).and Zn2.88Co0.12V3O8(640.4 m Ah·g-1),but after 80cycles,the discharge specific capacity of Zn3V3O8/Fe3O4 decayed to 369.5 m Ah·g-1,which was more serious than that of Zn3V3O8(566.8 m Ah·g-1)and Zn2.88Co0.12V3O8(652.2m Ah·g-1).The impedance test showed that the charge transfer resistance of Zn2.88Co0.12V3O8was the smallest among three samples.Therefore,Zn2.88Co0.12V3O8 behaved outstanding electrochemical cycle performances as an anode material.(2)The BiVO4/Fe VO4 composites with different molar ratios were synthesized through a solvothermal method using Bi(NO3)3·5H2O and Fe(NO3)3·9H2O as raw materials.The structure and morphology of the composites were characterized by X-ray diffraction(XRD)and scanning electron microscopy(SEM).The results showed that the morphology of the composite could be affected by adjusting the ratio of Bi3+to Fe3+.The synthesized BiVO4/Fe VO4(1:1)composite took on morphology of microrods with a length of about 3-7?m and also contained some micron particles with diameter of 100 to 350 nm.The Electrochemical performance tests showed that the discharge specfic capacity of BiVO4/Fe VO4(1:1)composites was 417 m Ah·g-1 after 100 cycles,which was higher than that of pure BiVO4(204.7 m Ah·g-1),Fe VO4(291.1 m Ah·g-1),and other composites(such as BiVO4/Fe VO4(2:1)(383 m Ah·g-1)and BiVO4/Fe VO4(1:2)(220.5 m Ah·g-1)).And also,the charging platform of the BiVO4/Fe VO4(1:1)was relatively low(about 0.9 V),so the BiVO4/Fe VO4(1:1)composite was a promising anode material for lithium-ion battery application.(3)Pure cerium vanadate(Ce VO4)nanoparticles were prepared by one-step hydrothermal method using Ce(Ac)3·x H2O and NH4VO3 as raw materials,water and ethylene glycol as solvents,and the Ce VO4 was compisited with Fe3O4 in different mole ratios.The expected products were characterized by X-ray diffraction,scanning electron microscopy and x-ray photoelectron spectroscopy techniques.The electrochemical performance test results for diffrent products showed that Ce VO4/Fe3O4 nanoparticles had higher specific capacity and better cycle performance than that of Ce VO4 prepared under the same conditions.The initial specific discharge capacities of Ce VO4 and Ce VO4/Fe3O4-2 as anode materials were 671.7and 964.0 m Ah·g-1,respectively.After 100 cycles,the specific discharge capacities for the two samples remained at 416.4 and 875.9 m Ah·g-1,corresponding to capacity retention rates were 62%and 91%,respectively.In addition,Ce VO4/Fe3O4-2 had better rate performance than those of other products.When the current density was 2 A·g-1 and voltage window was between 0.01-3V,the discharge specific capacity of Ce VO4/Fe3O4-2 was about 550 m Ah·g-1.when the current density returns to 100 m A·g-1,the discharge specific capacity of Ce VO4/Fe3O4-2 can go back to 745 m Ah·g-1.What is more,the prepared Ce VO4/Fe3O4nanocomposite electrode had smaller charge transfer impedance and larger lithium ion diffusion coefficient.The smaller polarization degree during charging and discharging process can lead Ce VO4/Fe3O4 composite to behave excellent electrochemical performance among all samples. |
PDF Full Text Request