Study On Lithium Storage Properties Of Transition Metal Phosphides And Selenides

In recent years,lithium-ion batteries are one of the best choices for energy storage equipment because of its high energy density.The electrode material is a key factor determining the performance of lithium-ion batteries.At present,the theoretical specific capacity of commercial graphite as an anode material is low.Therefore,it is urgent to develop new anode materials.It is found that the metal phosphides and selenides have a higher theoretical specific capacity.The metal selenides are also beneficial to increase specific capacity because of its large interlayer distance and conversion reaction mechanism.These advantages of the two compounds have attracted much attention,but their electrical conductivity is poor,and the discussions of the metal selenide lithium storage mechanism are not the same.Thus,this paper focuses on the lithium storage properties and modification methods of NiCoP and the lithium storage mechanism of CoSe and CuInSe₂.The specific content is as follows:1.A variety of metal phosphides are prepared by the hydrothermal method and used in anode material of lithium-ion batteries.Through comparison of lithium storage performance,it is found that the performance of bimetal phosphide is better than single metal phosphides.In addition,the reasons for improving the lithium storage performance of NiCoP by adding carbon nanotubes are discussed.The study find that carbon nanotubes distributed on the surface and inside of NiCoP can effectively improve the conductivity of the composite and activate the lithium storage activity of the internal material.As an anode material for lithium-ion batteries,the specific capacity of NiCoP/CNTs can reach 200 mA h g^-1 after 200 cycles under the current density of 100 mA g^-1.2.The petal-like CoSe is prepared by hydrothermal method,and its lithium storage mechanism is studied.During the charge/discharge cycles,the capacity of the CoSe decreases first and then increases.In the initial stage,the volume of CoSe expands due to the intercalation of Li⁺,which results in the amorphousness of CoSe and reduces the specific capacity.The subsequent increase in specific capacity is due to the recrystallization of the material and the formation of a conductive SEI film.The petal-like CoSe displays a specific capacity of 450 mA h g^-1 at the current density of 100 mA g^-1 after 300 cycles.In order to improve the lithium storage performance,a CoSe/rGO composite is prepared.The addition of GO during the preparation of CoSe changes the morphology of CoSe from a larger petal shape to a smaller rod shape,which weakens the effect of volume change during Li⁺intercalation and shortens the Li⁺diffusion distance,so improves the reduction of specific capacity in the initial stage.At a current density of 100mA g^-1,the specific capacity of CoSe/rGO composite can be as high as 730mA h g^-1 after 200 cycles.Even under a large current density of 1000 mA g^-1,the specific capacity of the CoSe/rGO composite can still reach 570 mA h g^-1after 1000 cycles.3.The CuInSe₂ is prepared by the hydrothermal method and used as an anode material for lithium-ion batteries.The lithium storage mechanism is discussed by ex-situ XRD and XPS tests.It was found that the lithium storagemechanism of CuInSe₂ is different from previous studies.When Li⁺is inserted into CuInSe₂ material,no conversion reaction occurs to generate Cu,In,and Li₂Se,but only lithiation/delithiation reactions occur.At the current density of 100 mA g^-1,the first discharge specific capacity of the material is 514.7 mA h g^-1.