Preparation Of Transition Metal Sulfide/Selenide Anode Material And Lithium Ion Battery Storage

In recent years,the development strategy of new energy has been upgraded to the national level,and the state has also increased research and development efforts in terms of new energy power batteries.Whether people can effectively improve the energy density of lithium-ion batteries to meet the cruising range is an important factor in determining the success or failure of new energy vehicles.Current methods for increasing the energy density of lithium-ion batteries include the development of positive and negative materials,electrolytes and separators.The development of new electrode materials is an important and feasible solution.At present,a variety of new materials such as transition metal oxides,sulfides and silicon-based materials have been developed and used to replace traditional graphite materials for lithium ion battery anode materials.Among these materials,transition metal sulfide/selenide has a large rate performance due to its unique graphene-like structure,and thus becomes one of the important candidates for the anode material of lithium ion batteries.This thesis has done the following three work on the development of a transition metal sulfide/selenide anode material and lithium ion battery performance:1.The hierarchical structure of MoS₂ nanosheets was directly prepared by etching the MoO₃ nanowire precursors by sulfur source.Due to the advantages of large surface area,many active edges and high conductivity,the hierarchical structure of MoS₂ nanosheets has been studied in lithium ion batteries and supercapacitors.When used as a negative electrode for lithium-ion batteries,at a current density of 0.2 A g^-1,the specific capacity is still as high as 850 mAh g^-11 after 100 cycles,and the coulombic efficiency is close to100%.In the asymmetric supercapacitor test,at a current density of 2 A g^-1,the specific capacity remained at 1386 F g^-1after 5000 cycles,and coulombic efficiency was basically99.8%.Reasonable design is also applicable to the etching of other transition metal oxides,which provides an effective way and method for improving electrochemical performance.2.The defect-rich MoS_2（1-x）Se_2xx nanocomposites were prepared by sulfur and selenium,and the ratio of sulfur to selenium was adjusted while maintaining the structural integrity of the skeleton.The effects of different sulfur-selenium ratios on the morphology and structure of MoS_2（1-x）Se_2xx nanomaterials were systematically studied from experimental data and theoretical calculations.The properties of lithium-ion batteries were studied for the optimized materials.For example,because MoS_2（1-x）Se_2x（x=0.25）nanomaterials have the advantages of few layers,large surface area,many defects,high conductivity,etc.,at a high current density of 5C,the specific capacity is still as high as 500 mAh g^-1after 350cycles,coulombic efficiency close to 100%.A rational design is also applicable to other transition metal sulfides or selenides,which provides new ways and means to improve battery performance.3.The CuS micron flowers structure with adjustable layer spacing is assisted by halogen ions in a low temperature solvothermal reaction.The layer spacing of the crystal plane（002）was found to increase from 0.88 nm to 1.35 nm by characterization.The effects of different kinds of halogen ions on the morphology and structure of CuS micron flower were systematically studied.The optimized CuS micron flowers was studied as a negative electrode material for lithium ion batteries and sodium ion batteries.The CuS(Cu²⁺/Cl^-=2:4)micron flowers as an anode for LIBs reveals a high reversible capacity of800 mAh g^-1at 0.2 A g^-1,and 502 mAh g^-1at 2 A g^-1after 750 cycles with no significant capacity degradation.The CuS(Cu²⁺/Cl^-=2:4)micron flowers as an anode for SIBs reveals a reversible capacity of 381 mAh g^-11 at 1 A g^-1.The excellent electrochemical performance is attributed to the unique structure of this material,and the large layer spacing ensures its high rate performance.As a conversion electrode material for high performance LIBs or SIBs,this novel strategy is expected to be an efficient and feasible method for preparing other layered metal sulfides.