Preparation Of MoS₂ Nanomaterials And Study On Their Electrochemical Properties

Due to the large capacity,small size,safety,portability and non-pollution,Lithium-ion batteries have been developed into important energy storage devices in many fields such as electronic products,artificial satellites,military industries,and smart grids.However,graphite,which has been commercialized as an anode material for lithium ion batteries,has a low theoretical specific capacity value of 372 m Ah/g cannot meet the increasing demand for lithium ion batteries.Therefore,exploration of new anode materials with high capacity value and long cycle stability is an important part in the development of lithium batteries.In recent years,molybdenum disulfide is expected to be a new generation of anode material with better performance due to its layered structure,similar to graphene,high capacity?670m Ah/g?and low raw material cost.However,the molybdenum disulfide has large surface energy and is unstable and easy to stack;the insertion and extraction of lithium ions during charge and discharge will cause a large deformation,and the structure is easily broken;in addition,molybdenum disulfide,as a semiconductor material,has poor conductivity.Therefore,as a lithium battery anode material,molybdenum disulfide has great limitations in practical applications.This article aims at above issues,through the preparation of molybdenum disulfide nanocomposite electrode,cobalt doped molybdenum disulfide materials and other transition metal sulfide compounds—MoSe₂ research,preparing three anode materials with high specific capacitance,fast ion kinetics and long cycle life.In order to improve the electrical conductivity and stability of the MoS₂ electrode material,the MoS₂ is compounded with other more conductive sulfides.The MoS₂/Co₉S₈ composite electrode is prepared in situ on the carbon paper by the hydrothermal method,and thus improving the specific capacitance and conductivity of the material.The in-situ preparation of the composite structure on the conductive substrate can avoid the agglomeration and stacking of MoS₂ nanosheets and the synergistic effect of different material combination can improve the stability of the overall structure,and thus obtain a high-performance MoS₂ composite electrode material.Studies have shown that the optimal structure of the MoS₂/Co₉S₈ composite electrode has a better specific capacitance and conductivity than the single MoS₂ electrode material,and its specific capacity remains at 677 m Ah/g after 100 cycles of charge and discharge,which is four times the specific capacitance value of the molybdenum disulfide electrode material alone.In order to improve the performance of MoS₂ material itself,cobalt-doped MoS₂ electrode materials were prepared by hydrothermal method using different contents of cobalt nitrate,and the effects of doped cobalt on specific capacitance,conductivity,and cycle stability of MoS₂ were studied.The results of experiments show that appropriate cobalt doping will not significantly change the morphology of MoS₂ nanomaterials,but the cobalt atoms,doping into the MoS₂ lattice will introduce extra vacancy defects into the?100?crystal plane,which promotes lithium ion in the electrolyte to enter the interior of the MoS₂ electrode material through these defect sites.In addition,cobalt doping can also improve the conductivity of the material.Therefore,the cobalt-doped MoS₂ electrode material has better cycle stability than the pure MoS₂ electrode,and the capacity is 426 m Ah/g after 100 cycles of charge and discharge,which is maintained at 65% of the initial and better than original MoS₂.Finally,we extend our research ideas to MoSe₂ materials which has similar structure and properties of MoS₂.The hydrothermal method is used to prepare the precursors on two-dimensional graphene nanosheets.Then,the precursors are selenized by a tube furnace to make the MoSe₂ nanosheets uniformly disperse on graphene nanosheets.The precursor is obtained under the condition of cobalt nitrate to finally obtain cobalt-doped MoSe₂/graphene composite materials.The graphene allows the MoSe₂ nanosheets to grow uniformly,avoiding their agglomeration and increasing the contact between the electrode material and the electrolyte.Cobalt atoms also introduce defects in the MoSe₂ lattice,increase the reactive sites of the material,and accelerate the ion diffusion in the electrode material.For electrochemical performance test,the Co-MoSe₂/G electrode material have a increasing capacity and activation process during the earlier stage of constant current charge-discharge process.After 100 weeks of charge and discharge,the capacity value can reach 492 m Ah/g and the specific capacity after 200 cycle is about 320 m Ah/g,which is 137% of the capacitance of the initial.