Study On Synthesis Of Oxovanadium Compounds Cathode Materials And Their Electrochemical Performance For Lithium-ion Batteries

The NH4V3O8 material is proposed on the basis of LiV3O8 electrode materials,which has attracted extensive attention of researchers in recent years.NH4V3O8 materials have the characteristics of abundant raw materials,simple preparation,high capacity and good safety performance.It also has photocatalytic properties,electrical conductivity,lithium storage and sodium storage properties.Compared with the LiV3O8,NH4+ can enlarge the interlayer spacing and the formation of intramolecular hydrogen bonds due to the presence of H+,which can effectively improve the stability of the material structure.This is a cathode material with good development prospects.At the same time,it can also be applied to supercapacitor materials,sensor materials and nanometer electronic devices by virtue of its unique structure and electron transport characteristics,which has a wide range of applications and research prospects.Although NH4V3O8 has good electrochemical performance,the low electrical conductivity of NH4V3O8 and ion mobility makes the capacity decay and small energy density during high current charge and discharge.As a positive electrode material for lithium ion batteries,charge and discharge performance needs to be further improved.The dissertation mainly uses solvothermal methods to prepare NH4V3O8 micro-nano particles with different morphologies and different sizes.At the same time,the appropriate carbon materials are selected and the experimental process is explored to realize the bonding and recombination of NH4V3O8 and carbon materials.Prepared nitrogen-doped carbon layer-coated V2O5 materials and cobalt ion-doped V2O5,as the cathode material for lithium-ion batteries,both show good lithium storage performance.This thesis has mainly obtained the following research results:(1)Through the solvothermal method,a 3D flower-shaped spherical NH4V3O8 material with controlled morphology was successfully prepared.By adjusting the pH of the solution to 4,the cycle and rate performance of the battery is better.When current density is 15 mA g-1,the discharge capacity of the sample can be maintained at 365 mAh g-1.After 50 cylcles,the retention rate of specific discharge capacity is 83.8%.By adjusting the type of reaction solvent,the morphology of NH4V3O8 can be effectively controlled.When the reaction solvent is a mass ratio of ethanol to ethylene glycol of 2:1,the shape of the hollow nanotubes is rectangular,providing moreactive site for lithium ion.(2)The composite material of NH4V3O8 and Super P was successfully prepared.The spherical Super P between the NH4V3O8 sheets plays a role of bridging and connecting the NH4V3O8 sheets.It has built a bridge for electron transport and ion diffusion between the NH4V3O8 sheets,which improves the electrical conductivity and lithium ion diffusion coefficient.Meanwhile,rGO/NH4V3O8 composites were also prepared.The maximum discharge capacity of the sample 253 mAh g-1,when the current density is 15 mA g-1.After a series of cycles,the capacity retention rate remainted stable at 88%.(3)V2O5 with nitrogen doped carbon coating was synthesized by organic solvent assisted in-situ hydrothermal growth method.The doped nitrogen atom can not only improve the electronic conductivity but also the specific discharge capacity.After cycling through different current density,the capacity retention rate is 90%,which improve the lithium storage performance.(4)Through solvothermal synthesis,cobalt-doped V2O5was successfully prepared by using anionic surfactant to assist the growth of V2O5 precursor.Through the control of cobalt ion content,we can control the size of V2O5 nanobelt and the growth of nanosheet.When the cobalt ion content was 5%,the electrochemical performance was the best.After the cobalt ion doped,the lattice parameters of the samples V2O5are enlarged,which is conducive to the diffusion and transfer of Li+.