Study On Preparation And Lithium/Sodium Storage Properties Of Transition Metal Selenide

In this dissertation,we focus on the research of FeS_1.6Se_0.4,FeSe₂ and MoSe₂,respectively,to improve the cycle performance and rate capability of transition metal selenides.By means of doping of impurities,synthesis of composites,construction of nanostructures,the electrochemical performance of all the above mentioned electrodes for Li-ion batteries?LIBs?and Sodium-ion batteries?SIBs?can be improved.The main research contents and results are as follows:?1?FeS₂ and Se-doped FeS_1.6Se_0.4 are prepared by facile hydrothermal method.They have the similar morphologies and are microspheres,but the diameter of FeS_1.6Se_0.4?1?1.5 ?m?is only half of that of FeS₂,which means that FeS_1.6Se_0.4 has a higher specific surface area.FeS_1.6Se_0.4 has the typical characteristics of sulfide/selenide,the solid solution of S/Se in FeS_1.6Se_0.4 enables it to have better performance than FeS₂.When it is applied for LIBs,the reversible capacity of FeS_1.6Se_0.4 is 481.0 mAh/g after 200 cycles at 200 mA/g.Even at the high current density of 2 A/g,the reversible capacity can still achieve 290.6 mAh/g.?2?FeSe₂/rGO composite is synthesized by one-step solvothermal method.The clusters assembled of FeSe₂ nanorods are anchored on the graphene oxide.The excellent ductility and conductivity of graphene oxide not only prevent FeSe₂ to agglomerate and buffer the volume expansion,but also provide a continuous conductive network which improves the conductivity of the material.Therefore,FeSe₂/rGO has better electrochemical performance than that of pure FeSe₂.As an anode material for LIBs,the FeSe₂/rGO electrode delivers a reversible capacity of 518.2 mAh/g after 200 cycles at a current density of 500 mA/g.The rate performance is tested at different current rate from 50 mA/g to 1 A/g,and each current density runs 5 cycles.Even the current density at 1 A/g,FeSe₂/rGO still can deliver a capacity of 728.0 mAh/g.In addition,due to the pseudocapacitive behavior,the measured specific capacity of FeSe₂/rGO is larger than the theoretical capacity.?3?Hollow MoSe₂ microspheres are prepared by solvent-thermal method.The diameter of MoSe₂ microsphere is about 1.5 ?m.The surface of MoSe₂ microsoheres is assembled by numerous MoSe₂ nano-flakes.The gaps between the flakes constitutes a porous structure.The interlayer spacing of the?002?plane observed by HRTEM is 0.67 nm.MoSe₂ shows good cycle stability and rate performance for the SIBs.After 250 cycles at a current density of 250 mA/g,the reversible capacity of MoSe₂ microspheres is 325.0 mAh/g,and the reversible capacity remains 262.4 mAh/g at a current density of 1 A/g.When the current density is restored to 250 mA/g,the reversible capacity is also recovered to 456.9 mAh/g.