Synthesis And Electrochemical Properties Of M_xV_yO_z(M=Li,Co,Zn)Anode Materials For Lithium-Ion Batteries

In recent years,the vanadium-based metal-oxide anode material for lithium-ion batteries,such as Li3VO4 and Co(Zn)xVyOz,have attracted extensive attention due to their good lithium storage performance.Li3VO4 has a suitable working potential,high reversible capacity(?600 mAh g-1)and small volume change(4%)during lithiation-/delithiation process.Co(Zn)xVyOz has a higher specific capacity and good cycle stablility due to the multiple lithium storage mechanism and the intrinsically synergic effects of the metal species.However,these materials suffer from the low electronic conductivity and unstable structure during long-term lithiation/delithiation process.In order to overcome these shortcomings,we have attempted to improve the electrochemical performance of these vanadium-based materials by different means,include element doping and compositing,mophology design,and so on.The main contents of this thesis are as follows:(1)The intrinsic conductivity of Li3VO4 material was successfully tunned by Ca/Na element doping at Li site,resulting into an excellent electrochemical performance.Among the Ca/Na-doped series samples,Li2.97Ca0.03VO4 and Li2.95Na0.05VO4 exhibit the best electrochemical performance.Li2.97Ca0.03VO4 delivers high capacities of 385.8 mAh g-1at 1 C after 180 cycles with capacity retension of 94.9%,and the reversible specific capacity and capacity retention of Li2.95Na0.05VO4 are 398.3 mAh g-1 and 100%,respectively,when measured at 1 C after 150 cycles.The improved electrochemical performances of these Ca/Na-doped Li3VO4 are originated from the improved electronic conductivity,expanded lattice and suppressed particle agglomeration during the material preparation process.(2)The sponge-like hierarchically porous Li3VO4@C was prepared on a nickel foam substrate by the electrostatic spray deposition(ESD)technique.Li3VO4@C material shows outstanding electrochemical properties.It delivers a high capacity of 399 mA h g-1 at the rate of 10 C after 1000 cycles with capacity retension of 100%.The excellent electrochemical performance can be ascribed to the unique morphology can significantly increase the surface area of the material,shorten the diffusion distance of Li+ and accomodate the volume change of the material during charge/discharge process.The nickel foam substrate can act as an electric transport network and a structural supporting for the active material.In addition,the coated carbon network can further facilitate the transmission of electrons in the material.(3)A carbon-coated Zn2VO4/ZnO composite with porous structre was sucessfully prepared through the electrostatic spray deposition method.It delivers a high specific capacity of 930.8 mAh g-1 at 2 A g-1 even after 800 cycles without any capacity fading.The outstanding electrochemical performance of the material can be ascribed to the porous morphology,which can stable the structure of the active material during charge and discharge process,and the coated carbon layer can improve the electronic conductivity of the material.(4)The carbon-coated mesoporous Co2VO4 microspheres were prepared by a solvothermal method.It delivers a high reversible capacity of 929.8 mA h g-1 with the capacity retention of 103.6%at a current density of 1 A g-1 after 400 cycles.At a high current density of 10 A g'1,the capacity can still maintain at 298.1 mA h g-1.The excellent cyclic stability and rate performance are attributed to its unique architecture,which can effectively shorten the diffusion length of Li+,improve the specific surface area,and accommodate the volume variation of the electrode materials during charge/discharge processes.'In addition,the coated carbon layer can further improve the electronic conductivity of the material.(5)The mesoporous core-shell Co3V2O8(CVO-1T)microspheres were prepared through a solvothermal method under 1 T magnetic-field.Compared to the solid mesoporous Co3V2O8(CVO)microspheres prepared without magnetic-field,CVO-1T has a better electrochemical performance.CVO-1T can deliver a high reversible specific capacity of 1210.3 mAh g-1 at a current density of 0.5 A g-1 after 100 cycles and with a capacity retention of 105.2%.However,the corresponding values of CVO material are only 885.2 mAh g-1 and 96.5%.The unique core-shell structure contributes mainly to the excellent electrochemical performance of CVO-1T material,which can considerably alleviate the volume change during the Li+intercalation/deintercalation process.