Study On Catalytic Performance And Mechanism Of Modified Molybdenum Disulfide Matrix Composites For Lithium-Sulfur Batteries

With the accelerating process of industrialization and information technology,new requirements are put forward for the new generation of energy storage equipment.Over the past 30 years,Lithium ion batteries（Li Bs）have re volutionized the field of energy storage devices.However,with the deepening of research,the current energy density of Li Bs is approaching the limit,and the development of new technologies is of great significance for the realization of the next generation of high energy storage.Lithium-sulfur batteries（LSBs）is expected to be one of the next generation energy storage devices due to its high specific capacity(1675 m Ah g^-1),high energy density(2600 Wh kg^-1)and environmental friendliness.However,the shuttle effect caused by‘solid-liquid-solid’reaction mechanism has an adverse effect on its electrochemical performance,which seriously restricts the practical application of LSBs.In this dissertation,MoS2,as a typical catalyst,was modified and used for separator modification of LSBs.The adsorption and catalytic effect on polysulfides,as well as the nucleation and growth mechanism of Li2S induced by MoS2 matrix composites materials were ayatematically studied.The main research contents are as follows:（1）Molybdenum dioxide-Molybdenum disulfide（MoO2-MoS2）for constructing high activity heterogeneous reaction interfaceUsing carbon nanotubes（CNTs）,MoO3 and S powder as precursors,the MoO2-MoS2heterostructure supported by CNTs were prepared by a simple high-temperature partial sulfurization method.CNTs improved the conductivity,and the MoO2-MoS2 heterostructure can not only combine the high adsorption capacity of MoO2 with the high catalytic activity of MoS2,but also provide a heterogeneous interface with a high activity for the catalysis of polysulfides and the nucleation of Li2S.As a result,the as-prepared MoO2-MoS2-CNTs/PP separator successfully optimized the REDOX kinetics and improved the utilization rate of S species,thus significantly improving the cycle stability and rate performance of LSBs.（2）N-doped graphene uniformly loaded molybdenum disulfide（MoS2-NG）for enriching catalytic active sitesDifferent from simply growing MoS2 on graphene,a number of active sites that can uniformly adsorb Mo7O24^6-were constructed by loading polyaniline（PANI）to change the surface charge property of graphene,so as to achieve the goal of uniform growth of MoS2nanoflowers on surface of graphene,effectively avoiding agglomeration of MoS2 nanoflowers in the hydrothermal reaction.N-doped graphene enhanced the conductivity.Meanwhile,due to the increase of layer spacing of MoS2,a large number of interlayer active sites were exposed,improving the adsorption and catalytic activity for polysulfides.When MoS2-NG used for separator modification,its excellent catalytic performance can effectively inhibit the shuttle effect and accelerate the conversion of polysulfides into final product Li2S,promoting the specific capacity and cycle stability of LSBs.（3）Inducing the growth of Li2S（100）crystal plane by N-doping molybdenum disulfide（N-MoS2）An ultralsmall N-doped MoS2 nanocrystals anchored onto a porous N-doped carbon network（N-MoS2-NC）was prepared by thermal decomposition of the mixture of dicyandiamide（DICY）and ammonium tetrathiomolybdate（ATTM）.Porous N-doped carbon networks provided transport channels for electrons and lithium ions.The ultra-small size（2～5nm）and the property of N-doping of N-MoS2 nanocrystals offered a number of edge active sites,which played a significant role in promoting the catalytic conversion of polysulfides into Li2S.In addition,compared with pure MoS2,N-MoS2 nanocrystals can induce the preferentially oriented growth of Li2S（100）and promote the continuous growth of Li2S nanosheets along the direction perpendicular to the separator,effectively avoiding the cover of active sites caused by horizontal stacking of Li2S nanosheets and ensuring the ability of N-MoS2-NC to continuously promote the catalytic transformation of polysulfides.It also improved the electrochemical performance of LSBs.