Preparation And Electrochemical Properties Of MoS₂/C Alternating Intercalation Structure

Lithium-ion batteries（LIBs）have been widely used in all aspects of production and life because of their high specific capacity,long service life and green pollution-free characteristics.However,the limited lithium resources and increasing mining costs limit their further development.In contrast,sodium-ion batteries（SIBs）not only have the electrochemical intercalation behavior similar to LIBs,but also the sodium element of its main carrier is abundant and evenly distributed,so they are considered to be an ideal substitute for LIBs.However,the slow dynamic behavior of SIBs is easy to cause the rapid deterioration of doubling performance and the continuous attenuation of capacity,which makes it difficult to be applied in practical production and life.In order to solve this problem,researchers have studied a variety of metal materials such as carbon and sulfide.Among many SIBs negative electrode materials,MoS₂has attracted extensive attention because of its unique layered structure,high sodium storage capacity,diversity of synthetic processes and versatility of production and application.However,its small intrinsic conductivity and serious volume effect in the process of sodium ion insertion/removal limit the improvement of its electrochemical performance.Therefore,how to improve the conductivity and structural stability of MoS₂has become a research hotspot in the field of energy storage.In this thesis,carbon layers were successfully inserted between MoS₂layers by simple solvothermal method combined with high-temperature annealing treatment.MoS₂/C alternating intercalation structures with different layer spacing were obtained,and the effects on their morphology,composition and electrochemical properties were discussed.The research contents of this thesis are as follows:1.N-doped carbon layers were successfully inserted into adjacent MoS₂monolayers by solvothermal method combined with carbonization process,and ultra-thin layered MoS₂matrix composites with interlayer expansion were prepared.This structure can not only shorten the diffusion path of Na⁺,provide more Na⁺storage sites,but also significantly improve the conductivity of the material.The successful preparation of the alternating intercalation structure of MoS₂and C was verified by XRD and HRTEM,and its structure and composition were characterized by Raman and XPS.The prepared MoS₂-C/T/C composite has a reversible specific capacity of311.26 m Ah g^-1at a high current density of 10000 m A g^-1.After 3000 cycles at 1000m A g^-1,the capacity can be maintained at 338.31 m Ah g^-1,showing excellent rate performance and cycle stability.2.Through a simple one-step hydrothermal method,1,8-octanediamine was successfully inserted between MoS₂layers.After high-temperature annealing,1,8-octanediamine inserted between MoS₂layers formed an N-doped carbon layer,and hollow nanospheres with MoS₂/C alternating intercalation structure were successfully prepared.The hollow structure can effectively alleviate the volume change in the electrochemical reaction process and promote the infiltration of electrolyte.In addition,the insertion of N-doped carbon significantly improves the electron transport rate of the material,shortens the diffusion path of Na⁺,and provides more active sites.Thanks to the synergy between the hollow structure and MoS₂/C alternating intercalation structure,MoS₂/m-C₂₀has a reversible specific capacity of 463.3 m Ah g^-1at a current density of 0.1 A g^-1.At the same time,after 500 times of charge and discharge at a high current density of 1.0 A g^-1,the capacity can be maintained at 315 m Ah g^-1,showing excellent cycle stability.3.A variety of different organic amines（octylamine,decamine,dodecylamine,1,8-octanediamine,1,10-diaminodecane,1,12-diaminododecane）were used as intercalating agents.After simple solvothermal method and high temperature annealing treatment,MoS₂/C alternating intercalation structures with different layer spacing were prepared,and the controllable adjustment of MoS₂layer spacing was realized.The effects of different organic amine intercalators on their structure,composition and electrochemical properties were studied by means of XRD,Raman and XPS.Among them,the product obtained with 1,8-octanediamine as intercalation agent is named MoS₂/C-DOC.The material has large layer spacing（1.01 nm）and low graphitization（I_D/I_G=1.21）.When used as negative electrode material of SIBs,the material shows high reversible specific capacity(the specific capacity at 0.1 A g^-1current density is655.1 m Ah g^-1),good rate performance(specific capacity of 587.5 m Ah g^-1at 1 A g^-1current density)and cycle stability(323.9 m Ah g^-1after 500 cycles at 5 A g^-1).Based on this,the controllable adjustment of MoS₂layer spacing is realized by introducing different carbon substrates,and shows excellent electrochemical properties.