Induced Structure Evolution And Zinc Storage Properties Of CNFs/V₂O₅-PANI Composite Nanofiber Materials

Aqueous zinc-ion batteries（AZIBs）have received great attention due to their lower cost,higher safety,and sustainability compared to traditional lithium ion batteries.Vanadium based oxides are one of the cathode materials for AZIBs,and V₂O₅ is an important component.V₂O₅ has been widely studied due to its high theoretical capacity（589 m Ah/g）.However,during the charging and discharging process,the de embedding out of Zn²⁺can damage the open structure of V₂O₅,leading to structural instability,which seriously hinders the application of V₂O₅ in AZIBs.Therefore,polyaniline（PANI）molecules are pre embedded out in V₂O₅to form a PANI intercalated V₂O₅ material（V₂O₅-PANI）.This intercalated structure is conducive to alleviating the dissolution of V₂O₅ in aqueous electrolyte and weakening the strong electrostatic interaction between Zn²⁺and its host.On the other hand,combining cathode materials with conductive carbon materials can improve the conductivity of the materials,thereby promoting the progress of surface electrochemical reactions.Among them,electrospun carbon nanofibers（CNFs）have both one-dimensional charge transfer characteristics and three-dimensional porous structure characteristics,which are not only conducive to improving the charge transfer and transfer between the active cathode material and the electrode,but also conducive to the contact area between the active material and the electrolyte,promoting surface electrochemical reactions.In the research work,V₂O₅-PANI was combined with electrospun nitrogen-doped carbon nanofibers to improve its charge transport and surface reaction ability,and its interlaminar structure and electrochemical properties were regulated by heat treatment.In this work,the effects of heat treatment in an inert atmospheres at 300℃and 700℃on the structure evolution of CNFs/V₂O₅-PANI were investigated,and the effects of different temperatures on the structure evolution of CNFs/V₂O₅-PANI and zinc storage performance were explored.The main research contents are as follows:（1）The effect of annealing time（CNFs/V₂O₅-PANI、CNFs/V₂O₅-PANI-20min、CNFs/V₂O₅-PANI-PANI-60min、CNFs/V₂O₅-PANI-100min）on the structure evolution and zinc storage properties of CNFs/V₂O₅-PANI materials under nitrogen atmosphere at 300℃were studied.Four kinds of samples were prepared:CNFs/V₂O₅-PANI,CNFs/V₂O₅-PANI-20min,CNFs/V₂O₅-PANI-60min,CNFs/V₂O₅-PANI-100min.Through X-ray diffraction（XRD）experiments,it was found that with the increase of annealing time,the peak position corresponding to the（001）crystal surface of the sample gradually shifted to a small angle.However,when the annealing time reached 100 minutes,the diffraction peak changed from a sharp peak to a wide peak,indicating that the interlayer distance of the sample increased with the increase of annealing time,and the lattice gradually changed into disorder.When the annealing time is 60 min,CNFs/V₂O₅-PANI-60min have a clearly ordered layered structure with an interlayer distance of 1.47 nm.CNFs/V₂O₅-PANI-60-min sample,at a low current density of 0.1 A/g,has the highest capacity after annealing for 60 min,and is 580 m Ah/g after activation.At a high current density of 10 A/g,a reversible capacity of 113.2 m Ah/g can still be maintained.The capacity and yield of Zn²⁺were higher than those of the samples annealed at other times,which indicated that the ordered layer structure and large interlayer distance could promote the transport and reaction of Zn²⁺,which was beneficial to the improvement of electrochemical properties.In addition,the influence of surface and diffusion processes on Zn²⁺energy storage was revealed through CV curve fitting analysis.The diffusion coefficient of Zn²⁺was measured experimentally,ranging from 10^-8 to 10^-9 cm² s^-1 by GITT experiment.（2）The effect of annealing time on the structural evolution and zinc storage properties of CNFs/V₂O₅-PANI materials under 700℃nitrogen atmosphere was studied.The following four samples were obtained:V₂O₃-CNFs-20min、V₂O₃-CNFs-40min、V₂O₃-CNFs-60min and V₂O₃-CNFs-80min.Through X-ray diffraction characterization,it was found that V₂O₅ was quickly reduced to V₂O₃in the sample at high temperature,but there was no obvious layered diffraction peak when the treatment time was below 40 minutes.When the processing time reaches 40 min,the diffraction peak can be observed by XRD at about 7.5°.When the processing time is 60 min,the diffraction peak moves to 7.9°.Based on transmission electron microscopy（TEM）analysis,it is speculated that the disordered PANI molecular intercalation on the surface of CNFs/V₂O₅-PANI materials at high temperatures reduces the V-O layer and gradually converts it into an ordered carbon layer,The electrochemical performance test of the material formed carbon layer and inserted into the V₂O₃ was tested.The result showed that the samples treated for 60 min exhibited excellent electrochemical performance,with an initial capacity of 780 m Ah/g at a current density of 0.1 A/g,which is much higher than the samples treated for other times.The specific capacity is 360 m Ah/g at a current density of 1 A/g and can still maintain a specific capacity of 231 m Ah/g at a high current density of 10 A/g.In addition,non in-situ scanning electron microscope（SEM）observation of the surface morphology changes of the material during the charge and discharge process showed that the surface dense morphology of the sample before and after charge and discharge was almost identical,indicating that the material has good reversibility of the electrochemical charge and discharge process reaction.