Construction Of Transition Metal Tellurides/Sulfides And Their Electrochemical Properties

The application of lithium/sodium ion batteries in portable electronic devices and electric vehicles has attracted extensive attention.However,the commercial anode such as graphite/hard carbon has a low specific capacity,which is difficult to meet the requirements of high energy density/high power density for energy storage devices in modern society.Therefore,it is of great significance to find and develop advanced anode materials with high specific capacity and long cycle life for the development of the next generation of lithium ion（LIB）/sodium ion（SIB）batteries.Compared with carbon-based electrode materials,transition metal sulfide/telluride rely on conversion reaction to store energy,which has the advantages of high theoretical specific capacity and abundant reserves,and shows a broad prospect in the application of high energy density lithium/sodium ion battery anode materials.In this paper,Fe Te₂@Fe Te_1.5@C core-shell micron structure and Molybdenum disulfide@nitrogen doped carbon composite（MoS₂@NC）with anionic defects were synthesized by gas phase method,and their electrochemical energy storage performance and mechanism were studied.The research contents are as follows:（1）Synthesis of Fe Te₂@Fe Te_1.5@C core-shell microstructures with anion defects and their lithium ion storage properties.The anionic Fe Te₂@Fe Te_1.5@C core-shell microstructure of mil-88 precursor was constructed by the combined synthesis process of polydopamine coating and gas phase tellurization.The synthesized Fe Te₂@Fe Te_1.5@C sample shows a micron-sized rod shape,consisting of a thin N-doped carbon coating,internal Fe Te₂@Fe Te_1.5@C nanoparticles and the gaps between them.The unique structure of the N-doped carbon coating improves the electrical conductivity of the material and effectively alleviates the volume change during the electrode cycle.The presence of tellurium vacancies improves electrochemical kinetics by essentially increasing their electronic conductivity and providing redundant active sites for diffusion and storage of lithium ions.The Fe Te₂@Fe Te_1.5@C electrode exhibits A high discharge capacity of 700 m Ah/g after 300 cycles at A current density of 1 A/g,and a discharge capacity of 341 m Ah/g at a current density of 5.0 A/g,showing good long cycle capacity,long-term cycle stability and superior rate capacity.（2）Synthesis and electrochemical sodium storage of molybdenum disulfide@nitrogen doped carbon composite（MoS₂@NC）.Molybdenum disulfide@nitrogen doped carbon composite was synthesized by means of ammonium molybdate soaking polyaniline nanorods and gas phase sulfurization.In the electrode materials,MoS₂ exists in two forms:monolayer structure embedded in nitrogen-doped carbon（NC）material and nanosheet growing on the surface of carbon nanorods.Compared with nitrogen-doped carbon nanorods,MoS₂/NC electrode materials show superior properties of sodium ion storage,such as high specific capacity（current density of 0.1 A/g,Specific capacity of 586 m Ah/g）,high rate performance（current density of 2 A/g specific capacity of 403.8 m Ah/g）and excellent cycle stability（capacity of 434.1 m Ah/g after290 cycles）.This synthesis method realizes the design of MoS₂/NC materials at the molecular level,and has a good application prospect in the design of high-performance hybrid electrode materials for sodium ion batteries.