Based On Commercial Graphene Modified Sulfur-based Composite Preparation And Electrochemical Performance Research

Commercialized lithium-ion batteries are subject to the specific capacity of positive and negative active materials,which is difficult to meet the needs of higher energy density.The theoretical specific capacity of elemental sulfur in the high-energy specific lithium-sulfur battery system is 1675mAh·g^-1,and the theoretical specific energy density can reach 2600Wh·kg^-1.Now,there are three major factors that hinder the commercial production of lithium-sulfur batteries:?1?The elemental sulfur,reaction products Li₂S₂ and Li₂S have poor electronic conductivity and ionic conductivity,resulting in low utilization of active materials and rapid capacity degradation.?2?The elemental sulfur,reaction products Li₂S have a large density difference.In the process of charging and discharging,the large volume changes can destroy the electrode structure,leading to the dissociation of sulfur,resulting in the attenuation of capacity.?3?The long chain polysulfide of electrochemical reaction product,which is easily dissolved in electrolyte and migrates through the diaphragm between the positive and negative electrodes.We called this the shuttling effect.That results in low Coulomb efficiency and faster capacity decay.Therefore,many scientific researchers have done a lot of research around the main aspects of positive electrode material modification,separator modification,electrolyte modification,and negative material modification.The modification of positive electrode material is particularly important and has significant effects.Based on the modification of sulfur composite positive electrode by commercial graphene.The influence of graphene/Molybdenum dioxide composite on the electrochemical performance of the sulfur electrode was studied by one-step hydrothermal method after optimization of the preparation process.At the same time,the conductive polymer poly?3,4-ethylenediothiophene?was prepared by in situ chemical oxidation reduction method,and the influence of the polymer on the electrochemical performance of graphene/sulfur composites was studied.All of the specific research is as follows:?1?Graphene/sulfur composites were prepared by a thermal melting process based on commercial graphene as the carrier of active material sulfur.The research results show that the quality of domestic commercial graphene is uneven.And the physical and chemical properties showed that commercial graphene was lamellar and multilayer graphene.The results of scanning electron microscope show that lamellar graphene can effectively cover sulfur and inhibit the agglomeration of sulfur particles.Compared with pure sulfur electrode,commercial graphene can effectively improve the electronic conductivity of composite materials and improve the cycle stability of the battery.?2?Based on the optimization of the preparation technology,graphene/molybdenum dioxide composite was prepared by one step hydrothermal method.And the influence of molybdenum dioxide load on the electrochemical performance of the sulfur electrode was studied.The results show that compared to graphene/sulfur electrode,the loading of molybdenum dioxide can effectively improve the electrochemical performance of the battery.This is mainly attributed to the polarity of Mo-O on the surface of the conductive metal oxide molybdenum dioxide,which can effectivelyadsorbpolysulfideandinhibitthe"shuttleeffect".Meanwhile,the graphene/molybdenum dioxide composite can effectively reduce the polarization of the battery and enhance the electrochemical stability of the composite.?3?The poly?3,4-ethylenediothiophene?/graphene/sulfur composites were prepared by in-situ chemical redox method,and their electrochemical properties were studied.The results show that in the composite structure,polyethylene?3,4-ethylene dioxythiophene?and laminated graphene jointly construct the three-dimensional conductive network structure,which is beneficial to the charge transport and shorten the diffusion path of lithium ions.At the same time,poly?3,4-ethylenediothiophene?was coated on the surface of graphene/sulfur composite materials,which can further inhibit the"shuttle effect"of polysulfide and improve the electrochemical performance.