Preparation And Lithium Storage Performances Of Graphene/Iron-Based Metal Selenide Composites

Metal selenides are a kind of compounds with high theoretical specific capacity,high electronic conductivity and large crystal plane spacing,making them more promising in the field of energy storage.In addition to the above advantages,iron-based metal selenides also have the characteristics of high electrochemical activity and semiconductor properties.In this thesis,three kinds of iron-based metal selenide composites were prepared by different synthesis methods,and the lithium storage performances of the composites were investigated in detail.The main contents of this thesis are as follows:Graphene/FeSe₂（RGO/FeSe₂）composites were prepared by hydrothermal method.The effects of hydrothermal reaction time and graphene content on the lithium storage performances of the RGO/FeSe₂ composites were investigated in detail.The hydrothermal reaction time affects the particle size of the FeSe₂ material,and graphene can further hinder its growth and agglomeration.The lithium storage performances of the RGO/FeSe₂-10 are the best when the hydrothermal reaction time is 6 h and the content of graphene is 10%,The discharge specific capacity is 709 m Ah g^-1 at 5 A g^-1.The reversible capacity is 1553 m Ah g^-1 after 400 cycles at a current density of 0.5 A g^-1.In order to further improve the capacity of FeSe₂ material,FeSe₂-Sn Se₂（Fe-Sn-Se）bimetallic selenide heterostructure was constructed.Graphene/FeSe₂-Sn Se₂（RGO/Fe-Sn-Se）composites were prepared by co-precipitation combined with vapor-phase selenization method.The effects of the synthesis process and graphene content on the lithium storage performances were investigated in detail.Adjusting the synthesis process can optimize the morphology of the product,and graphene can further maintain the integrity of its morphology.The lithium storage performances of RGO/Fe-Sn-Se-10 are the best when the concentration of Na OH is 2 mol L^-1during the synthesis of the precursor,the selenization time is 2 h and the content of graphene is10%.The specific discharge capacity is 782 m Ah g^-1 at 0.1 A g^-1.The reversible capacity is1002 m Ah g^-1 after 180 cycles at a current density of 0.5 A g^-1.In order to further improve its electrochemical activity,Sn element was doped into FeSe₂material.Graphene/Fe_0.95Sn_0.05Se₂(RGO/Fe_0.95Sn_0.05Se₂)composites were prepared by solvothermal method.The effects of Sn and graphene content on the lithium storage performances were investigated in detail.A proper amount of Sn doping can improve the conductivity of Fe_1-xSn_xSe₂ material and prevent its agglomeration The lithium storage performances of the RGO/Fe_0.95Sn_0.05Se₂-10 composites are the best when the doping amount of Sn is 5%and the content of graphene is 10%.The specific discharge capacities are 782 and659 m Ah g^-1 at current densities of 0.1 and 5 A g^-1,respectively.