Studies On Solid-State Chemical Synthesis And Performances Of V₂O₅ Cathode Materials For Lithium Ion Batteries

As a secondary energy device,lithium ion battery has high energy density and high power density,suitable for all kinds of electricity equipments and devices.The performance of the cathode material often determines the discharge specific capacity and cycle charge-discharge performance of lithium ion battery?LIB?.Therefore,the researchers have done a lot of exploration and research for the cathode material.They have developed a lot of cathode materials with high capacity and good charge-discharge performance,such as the lithium cobalt oxide,lithium nickel oxide,lithium manganese oxide and lithium iron phosphate and so on.However,these materials have still not enough high discharge capacity,or not enough good cycle stability for practical application.Therefore the exploitation of new cathode materials is still an urgent subject for researchers.V₂O₅ has special layered structure,can accommodate multiple Li⁺ as lithium ion cathode materials,thus exhibited high theoretical capacity,which have great potential for application in LIB.At present,synthetic methods of V₂O₅ nanomaterials mainly include hydrothermal method,solvothermal method,sol-gel method and so on.The synthesis of V₂O₅ nanomaterials by low-heat solid-state chemical reaction was not reported.This paper adopts the low-heat solid-state chemical reaction for synthesis of precursor,the method has the advantages of simple operation,without solvent?avoid causing environmental pollution?and be suitable for mass production.Then V₂O₅ nanomaterials were obtained by the calcination of as-prepred precursor.The electrochemical performance of the V₂O₅ nanomaterials as lithium ion battery cathode material were studied.Further research on modification for the performance of V₂O₅ nanomaterials was also carried out.The discharge specific capacity of V₂O₅ nanomaterials were increased by the doping of Cu element,and the long cycle stability were also improved by compounding with graphene.This thesis mainly includes the following three parts:?1?The precursor was first synthesized by room-temperature solid-state chemical reaction between ammonium metavanadate and organic acid.Then V₂O₅ nanomaterials are obtained by the heating-treatment of the precursor.The fluence of organic acid,the proportion of reactants,calcination temperature and other factors on the morphology and the electrochemical properties of V₂O₅ nanomaterials were investigated.The experimental results show that the organic acid,ratio of reactants,and calcination temperature have influence on the morphology of V₂O₅,and affect the electrochemical properties of V₂O₅.Under the synthetic condition that organic acid chooses tartaric acid,the rate of reactant is 1:2,and calcination temperature is 600?,the V₂O₅ nanomaterials have narrow size distribution,good dispersion and stable structure,and showed good electrochemical performance.Its discharge capacity can reach 235 mA g h-1.?2?In order to increase the discharge capacity of V₂O₅ nanomaterials,the cheap Cu element that have the high electrical conductivity second to silver was doped into V₂O₅ nanomaterials by solid-state chemical reaction,and the effect of the doping to the electrochemical properties of V₂O₅ nanomaterials was explored.Transition metal Cu makes the discharge capacity of V₂O₅ nanomaterials have an obvious increasement.When the doping amount of Cu element was 1%,the discharge capacity of the sample can reach 293 mA h g^-1.Because Cu²⁺ that have the radius slightly larger than the one of V⁵⁺ inserts into the lattice of V₂O₅,which will effectively broaden the ion channels and accommodate more lithium ion.But the crystal cell structure of V₂O₅ will happen some distortions after the doping of Cu²⁺,leading to the worse cycle stability of V₂O₅.?3?On the basis of previous work,in order to reinforce the cycle stability of the material,we synthesized rGO/Cu-V₂O₅ composite by a heating reflux method.The highly conductive graphene sheets could provide a fast electron conduction path to collect currents from V₂O₅.In addition,randomly stacked graphene sheets possess a mesoporous structure with a large electroactive surface,which facilitates formation of a good interface with the electrolyte.The cycle stability of the rGO/Cu-V₂O₅ composite has an obvious promotion.The capacity retention rate is 82.5% after two hundred cycles,compared with Cu doped sample?The capacity retention rate is 59.0%?,the capacity retention rate increased by 23.5%.