Preparation And Research On Carbon-based Composite Cathode For Lithium-sulfur Batteries

With the growth of population and the development of society,traditional energy can hardly meet the increasing needs of reality.Because of its high theoretical specific capacity(1675 mAh g^-1)and the low cost,environment-friendly and abundant reserves of the S cathode,lithium sulfur batteries?LSBs?have attracted extensive attention of researchers.However,before the commercialization of LSBs,there are some problems to be solved.Elemental sulfur and lithium sulfide are electron/ion insulators.,the huge volume expansion of elemental sulfur during the charge/discharge process,the circulating intermediate lithium polysulfide is easily soluble in electrolyte and causes"shuttle effect".The electrochemical performance of LSBs can be improved effectively by designing new composite electrode with good conductivity.In this paper,special precursors are selected,carbon/sulfur composite materials with novel structure are designed,and LSBs composite cathode with special porous conductive network with many active sites and good catalytic performance are prepared by MoS₂ cladding,and its electrochemical properties was studied.The specific research contents and results are as follows:?1?MoS₂@CZIF67/S composite anode was prepared by hydrothermal method and melting sulfur infiltration method.Among them,CZIF67 provides a complex porous conductive network as fast electron/ion transport channel.MoS₂ provides an external active site and work as a catalyst.In addition,the doped N can change the atomic hybrid structure of carbon,and improving its conductivity effectively.The electrochemical properties of MoS₂@CZIF67/S composite anode were significantly improved:An initial discharge capacity of 1047.2 mAh g^-1 is achieved at 0.5 C and the capacity retention is 88.3%after 200 cycles.Even under the current density of 1 C,the initial discharge specific capacity can up to 795.9 mAh g^-1,and the capacity retention is 74.9%after 400 cycles.The discharge capacity at 5 C is achieved 473.7 mAh g^-1.?2?The B-AC-CS/S composite electrode was prepared by traditional popcorn maker and melting sulfur infiltration which take cassia seed as a precursor.Among them,B-AC-CS provides a porous conductive network.In addition,natural N and P double doping can improve its conductivity and increase the active sites,effectively improving the electrochemical performance of the composite anode.The electrochemical performance of the B-AC-CS/S composite electrode was significantly improved compared with other two electrodes.The initial discharge capacity under the current density of 1 C is up to 1027.6 mAh g^-1,the discharge specific capacity remains at 982.2mAh g^-1 and the capacity retention is 95.1%after 100 cycles.Even under the current density of 5 C,the initial discharge specific capacity can up to 844.5 mAh g^-1,and the capacity retention is 97.8%after 100 cycles.?3?MoS₂@B-AC-CS/S composite electrode was prepared by coating MoS₂ on the surface of B-AC-CS by hydrothermal method and melting sulfur infiltration method.Among them,B-AC-CS provides a complex porous conductive network as fast electron/ion transport channel.MoS₂ on the surface provides an external active site and work as a catalyst.In addition,the doped N and P can improve the atomic hybrid structure of carbon,and improving its conductivity effectively.The electrochemical performance of MoS₂@B-AC-CS/S composite electrode has been greatly improved,and the initial discharge capacity under the current density of 1 C is up to 1167.9 mAh g^-1,the discharge specific capacity remains at 1079.9 mAh g^-1 and the capacity retention is 88.2%after 100 cycles.