Solvothermal Synthesis And Modification Of FeSe₂ Nanomaterials

FeSe₂,as an important transition metal selenide,has a special two-dimensional graphene-like layered structure and a high theoretical specific capacity?501 mAh·g-1?,which made FeSe₂ become the research focus of anode materials for Na-ion battery?SIBs?in recent years.In this paper,FeSe₂ nanomaterials were synthesized by solvothermal method.By optimizing relevant process parameters,the effects of different solvothermal parameters on the phase composition and morphology of final powders were discussed,the mechanism of FeSe₂ nanomaterials generation was clarified.And single phase FeSe₂ nano powder with flower-like morphology was obtained successfully.Subsequently,modification of the obtained FeSe₂ nanoparticles by adding surfactants to adjust the microstructure and carbon coating with different carbon materials.Combining the analysis results of the phase composition,microstructure and electrochemical properties of the composite materials,the mechanism of electrochemical performance changes caused by the process was systematically described.The main contents of the paper are as followsThe effects of different solvothermal parameters on the phase composition and microstructure of FeSe₂ nanomaterials were explored.Finally,single-phase FeSe₂ nano powder were successfully prepared,and the optimal solvothermal parameters for preparing single-phase FeSe₂ were obtained as:Se powder was used as the Se source,the reagent was added in the order of Se powder and FeCl2·4H2O,the solvent was a mixed solution of the volume ratio of ethylene glycol to NaOH solution was 1:3,the reactant molar ratio of Fe source to Se source was 1:2,the reaction temperature was 180? and the reaction time was 16 h.The amorphous carbon and graphene-coated FeSe₂@C composites were prepared by one-time hydrothermal carbon method and two-time hydrothermal carbon method respectively.Through systematic analysis of microstructure and electrochemical performance,it was found that the coating mechanism and FeSe₂ particle growth mechanism involved in several different coating processes are different.Among them,the advantage of one-time hydrothermal preparation of FeSe₂@C was that it can suppress the excessive growth of FeSe₂ particles and obtain a structure fully coated with amorphous carbon,and the charge-discharge performance and cycle performance are both great.The advantage of one-time hydrothermal preparation of FeSe₂@G was that the system has a higher electrical conductivity.While the two-time hydrothermal preparation of FeSe₂@C has the advantage of obtaining sufficient refinement of the powder and improving the specific discharge capacity of the system for the first time.By introducing EDTA-Na as a surfactant during the preparation process of the FeSe₂ nanomaterials,it was found that it can significantly affect the nucleation-growth kinetics process of the system,thereby obtaining FeSe₂ nanoparticles with different morphologies.The results of electrochemical performance measurements show that the columnar particles obtained after adding EDTA-Na have a larger size and grow to the micron scale during the carbon coating process,and the specific charge-discharge capacity of the system decreases.However,due to the reasonable carbon coating process,the cycle performance of different structures is better.