Design And Preparation Of Composite Materials Based On Molybdenum Sulfide And Its Application In Lithium Storage

In recent years,global energy demand and environmental issues have gradually attracted high attention from countries around the world.While promoting the development and utilization of new energy,how to realize the safe docking of renewable resources such as solar energy and wind energy with the grid energy storage system is the unremitting pursuit of the research and development field of energy converter components.The main challenge facing the green grid is to build a low-cost large-scale storage system,and clean and pollution-free lithium-ion batteries are the best choice as energy storage equipment.In fact,portable digital products have become an indispensable tool in life.As the energy supply device,lithium-ion batteries with high energy density and low self-discharge rate stand out among many secondary batteries and are widely used in many fields such as electronic consumption and new energy vehicle power system.However,the capacity and energy density of the traditional graphite electrode are relatively low,and new high-performance electrodes need to be developed to meet the technical requirements of the industry development.At present,the transition metal sulfide represented by molybdenum disulfide has unique physical and chemical characteristics and structural characteristics,and is a strong candidate for the next generation of electrochemical energy storage anode materials.Based on the above background,this work has designed and prepared composite electrodes with various structures using molybdenum disulfide.While obtaining excellent electrochemical performance,a detailed exploration of lithium storage mechanism and kinetic analysis of the electrode were conducted to provide feasible solutions for the production and development of transition metal sulfide negative electrodes.The main research work and innovation points include:（1）The core-shell CoS₂@MoS₂ nanorod arrays have been constructed on a hydrophilic carbon cloth substrate using a simple two-step hydrothermal reaction.The influence of reaction conditions on the synthesis of core-shell structure was revealed,and it was proved that the 1D structure of the composite electrode had a significant prompting effect on the diffusion of lithium ions.The carbon skeleton composed of carbon cloth provides a stable electrode structure and improves the overall conductivity of the composite.The close combination with the substrate avoids the loss of capacity caused by the separation of active substances.The surface MoS₂ nanoflakes are firmly wrapped in the outer layer of CoS₂ and form a porous core-shell structure,effectively inhibiting the accumulation of MoS₂.At the same time,it increases the number of active sites and provides more space to adapt to volume changes.One-dimensional structure not only shortens the diffusion distance of Li⁺,but also improves the specific capacity under the cooperation of CoS₂.Even after 500 cycles,the composite self-supporting electrode can still maintain a high capacity and cycle stability of about 600 m Ah g^-1at a current density of 2 A g^-1.Kinetic analysis shows that the composite electrode exhibits high pseudo-capacitance dominated charge transfer and fast lithium ion diffusion ability.This structure helps to understand the lithium ion storage mechanism under one-dimensional array structure,and provides a new strategy for designing reversible lithium storage anode with excellent performance.（2）The tubular CoS₂@MoS₂ composite was deposited on carbon cloth with metal-organic frame derivatives as precursors.The the growth of the array structure was summarized to construct the hollow nanotube structure.The reaction kinetics under the 1D layered structure design were clarified,and its excellent lithium storage capacity as anode was revealed and the corresponding stability was confirmed.The carbon cloth substrate provides a stable and highly conductive template for the integration of nanoarrays.By adjusting the reaction parameters,the morphology and density of the metal-organic framework derivatives are planned to achieve full contact with the electrolyte.The combination of outer MoS₂ and one-dimensional structure makes it uniformly distributed to avoid agglomeration and accumulation.The hollow structure provides more space on the basis of the nano-array to adapt to the volume expansion during the cycle.In the study of lithium storage mechanism,it is proved that the design of layered active substances shortens the ion diffusion path and promotes the charge transfer to realize the rapid charging and discharging process under the synergistic effect of components.Thus,the CoS₂@MoS₂/CC anode provides a high area-specific capacity and excellent reversibility of 2.35 mAh cm^-2 at a current density of 0.5 m A cm^-2 even after 100 cycles.In addition,electrodes show good ductility and foldability in flexible battery,showing potential value in flexible energy storage devices.（3）Three-dimensional multilayer conductive MoS₂@NCF/MoS₂ carbon nanofibers have been prepared by using electrospinning technology and hydrothermal process with MoS₂ as the main component.By analyzing the performance of one-dimensional to three-dimensional composite electrodes,the synthesis rules and structural advantages of hierarchical reactions were summarized,and the lithium ion storage mechanisms of active substances in different structures were clarified.The nitrogen-doped carbon nanofibers encapsulate the active material to avoid continuous capacity loss caused by direct contact with the electrolyte,and the conductivity of the composite is also improved.The embedded one-dimensional MoS₂ and the carbon fiber on the surface enhance the diffusion motion of Li⁺and promote the charge transfer at the interface.The layered structure improves the stability of the material and effectively alleviates the impact of volume change on the electrode.In the analysis of reaction kinetics,compared with the MoS₂ electrode under other structures,it is proved that the three-dimensional multilayer structure has a charge transfer mechanism dominated by enhanced pseudocapacitance behavior.Therefore,the MoS₂@NCF/MoS₂ electrode shows a high specific capacity of 736.7m Ah g^-1 and excellent reversibility even if it continues for 1000 cycles at a current density of 5 A/g.