Preparation And Electrochemicalperformance Of Composite Carbon Materials Based On Metal Organic Frameworks

In recent years,researchers have found that lithium-sulfur batteries with extremely high energy density(2600 Wh/kg)and theoretical specific capacity(1675m Ah/g)are expected to become one of the next generation energy storage systems.However,the practical application of lithium-sulfur battery is still hindered by many difficulties,including the poor conductivity of active material sulfur,the shuttle effect of intermediate lithium polysulfide(LPS)and the volume expansion of lithium sulfide.In order to solve the above problems,starting from the modification of cathode carrier materials and the design of sandwich materials for lithium-sulfur batteries,multifunctional zeolite imidazolyl skeleton-67(ZIF67),graphene,carbon nanofiber(CNF)composites(CZ@r)and cobalt doped carbon nanofiber(Co-CNF@CF)sandwich materials were synthesized by spray drying,natural sedimentation and chemical vapor deposition,and their preparation methods and properties were studied.The effect of different sulfur loading on the structure of cathode materials was investigated,and its electrochemical properties were studied deeply,which provides an important reference for the application research of lithium-sulfur battery.The main results are as follows:(1)ZIF67 graphene composites were prepared by spray drying,and rambutan-like CZ@r carrier materials containing carbon fibers were obtained by chemical vapor deposition.After high temperature treatment,the structure of loaded Co nanoparticles / multi-pore diameter microspheres was formed.The synergistic effect of reduced graphene and rich carbon fibers ensured the structural stability of CZ@r materials.The cycle life and electrical conductivity of the electrode are greatly improved.The abundant Co and N elements doping enhance the adsorption capacity of the carrier material and effectively improve the electrochemical performance of the electrode.The electrode has a discharge specific capacity of 1223.0 m Ah/g at current density of 0.2 C(2)The effect of sulfur loading on the electrochemical performance of S-CZ@r was studied.When the mass ratio of loaded active material to carrier material was 1: 3,the electrochemical performance of the composite was the best.After 100 cycles,the discharge specific capacity of the composite was stable at 967.5 m Ah/g.(3)Using ZIF67 and carbon fiber as precursors,ZIF67@CF interlayer was synthesized by natural sedimentation method.Co-CNF@CF sandwich material co-doped with carbon nanofiber and Co and N was prepared by chemical vapor deposition method using ZIF67@CF as template.The existence of Co and N can fix and adsorb the lithium polysulfide in the electrolyte and improve the utilization rate of active materials.The properties of several sandwich materials are compared and analyzed.The results show that the electrode materials obtained from Co-CNF@CF sandwich materials have good discharge capacity and cycle stability,and the Coulomb efficiency is 100% after the first discharge specific capacity is up to 1268.2m Ah/g,100 cycles at 0.2 C.