Study On Electrochemical Performance Of Co₃V₂O₈/RGO/C Nanofibers Anode Materials

The increasing threat of global warming due to the consumption of fossil fuels calls for new strategies to harness the inexhaustible supply of energy.Hence,developing clean renewable energy and safe power storage devices with high efficiency became one hot topic in the world energy study field.As a potential alternative to traditional energy sources such as oil,gas and coal,lithium-ion batteries are widely used in hybrid electric vehicles?HEVs?,medical devices and various portable electronic products,and will play an important role in supporting sustainable global economic growth and mitigating environmental impacts.Although graphite is a anode material for industrial lithium ion batteries with high reversibility,its low capacity(372 mAh g^-1)cannot meet the growing demand for high energy/high power density of the next generation of lithium ion batteries.In this regard,metal oxides,due to their large theoretical capacity,low cost,low toxicity and wide sources,are considered as alternative materials for graphite anode with broad application prospects.Cobalt vanadate,a binary metal oxide,has high electrochemical activity,which is the synergistic effect of cobalt and vanadium.In this project,electrostatic spinning technology,high-temperature calcination and hydrothermal reduction were used to prepare cobalt vanadatenanofibers?Co₃V₂O₈?,cobaltvanadate/graphenecompositenanofibers?Co₃V₂O₈/RGO?and cobalt vanadate/graphene/carbon composite nanofiber?Co₃V₂O₈/RGO/C?as anode materials for lithium ion batteries.The specific research content is as follows:?1?PVP/Co?NO₃?₂?6H₂O/C₁₀H₁₄O₅V composite nanofiber membrane with uniform diameter was prepared by electrostatic spinning technology.Co₃V₂O₈ nanofibers were calcined at 500?and 600?respectively.Morphology,composition and electrochemical properties of Co₃V₂O₈ nanofibers were characterized by thermogravimetric analysis?TGA?,X-ray diffraction?XRD?,scanning electron microscopy?SEM?,transmission electron microscopy?TEM?and electrochemical performance.XRD and SEM results showed that Co₃V₂O₈ nanofibers prepared at 600?had higher crystallinity,better fiber morphology and rough surface.BET results show that the material has a large specific surface area,which can increase the contact area between the electrode and the electrolyte and accelerate the diffusion rate of lithium ions and electrons.Electrochemical test results showed that,as a cathode material,Co₃V₂O₈ nanofiber had a discharge capacity of 1631 mAh g^-11 in the first week under the current density of 100mA g^-1,and the specific capacity remained at 412 mAh g^-1after 60charges and discharges.Even after a large current density cycle,the battery capacity can be restored to 587 mAh g^-1,showing a good capacity reversibility.?2?In order to further improve the electrochemical properties of Co₃V₂O₈ nanofibers,graphene oxide?GO?was added on the basis of the precursor solution of the first part.Electrostatic spinning technology and high-temperature calcining method were used to doped graphene on the surface of Co₃V₂O₈ nanofibers to prepare Co₃V₂O₈/RGO composite nanofiber anode materials.The results of electrochemical performance show a certain degree of improvement:at a current density of 50 mA g^-1,the initial charge and discharge specific capacity of Co₃V₂O₈/RGO composite nanofibers is 1216 mAh g^-11 and 1661 mAh g^-1,respectively.The discharge specific capacity through fully charge and discharge obtains 602mAh g^-11 after 100 times.Which compared to the electrochemical performance of elemental Co₃V₂O₈ nanofibers has improved.This is caused by the following reasons:the three-dimensional network structure channel can facilitate the rapid transfer of Li⁺between the electrode and the electrolyte.Graphene has unique electronic conductivity and good mechanical properties,which as a buffer framework,that inhibits the huge changes in the electrode volume.?3?Co₃V₂O₈/RGO/C composite nanofibers were successfully prepared by hydrothermal reduction method,high temperature carbonization combined with electrostatic spinning technology.The results of electrochemical properties exhibited that the discharge specific capacity of Co₃V₂O₈/RGO/C composite nanofiber reached 1342 mAh g^-11 in the first week under the current density of 50 mA g^-1,After 60 cycles,the specific capacity remained at1100mAh g^-1.Even though,at a high current density of 1000 mA g^-1,the reversible capacity remains at 334 mAh g^-1.And when the current density returns to 50 mA g^-1,the capacity can be restored to 1123 mA g^-1,showing excellent rate capacity.The improvement of electrochemical properties could be attributed to the following reasons:first,the porous structure of Co₃V₂O₈/RGO/C is conducive to the diffusion of lithium ions;Second,carbon nanofibers have high conductivity and reduce polarization under high current density.Thirdly,good conductivity of graphene can improve the conductivity of the whole material.Fourth,graphene as a buffer framework can effectively prevent the aggregation of active materials.