Construction And Electrochemical Properties Of Composite Cathodes For Lithium-Sulfur Batteries

Progress of science and technology promotes the continuous development of society.In order to meet the needs of human,all kinds of portable electronic equipment,high-power electric locomotives and mobile devices have come to our life.Now,lithium-ion battery is difficult to meet the needs of high-power equipment.Lithium sulfur battery attract more attention,due to higher energy density,and can meet the needs of high-power equipment.However,the problems of lithium sulfur battery bring huge hindrance to the application of high-power equipment,for example,the shuttle effect of lithium polysulfide,the poor conductivity of sulfur and lithium sulfide,and the volume expansion during charging and discharging.By rationally designing and constructing the structure of the positive electrode material,it aims to effectively solve the above-mentioned problems and improve the cycle performance of lithium-sulfur batteries.1.In order to behave the advantages of Ni-Co sulfide as a sorbent and catalyst for polysulfide.Ni-Co sulfides grown on Ni-foam was synthesized with a simple one-step hydrothermal method,which aims to increase the specific surface of nickel foam and provide enough space for the loading of sulfur.As a result of Ni-Co sulfide with complete mechanical structure at the macro level,it guarantees the integrity of the microstructure,using as hosts for lithium sulfur battery,which can ensures that Ni-Co sulfide can provide rich polar sites and catalytically active sites for polysulfides.The specific discharge capacity of the electrode is 1352.36 mAh g^-1 after 10 cycles at 1 C current density.2.Owing to Mo2C with the ability of catalyzing inert Li2S,PAN carbon fibers are used as the hard template and carbon source,and ammonium molybdate as the molybdenum source to prepare nano-scale Mo2C particles.This nano-scale Mo2C particles have a large specific surface and highly exposed active surface,which can effectively reduce the coating thickness of sulfur and enhance chemisorption and catalytic activity for lithium sulfide and lithium polysulfide.The capacity retention rate of cathode after 150 cycles is 69.66%.3.C@Ni/MnO nanofibers were synthesized via electrospinning and carbothermal reduction,where fibers are highly dispersed Ni particles on the surface.MnO particles are inserted in the network structure.With the functional adsorption layer of C@Ni/MnO nanofibers for lithium sulfur battery,Ni plays a role in catalyzing the conversion of polysulfide,and MnO can capture polysulfide.The synergistic effect of two component can effectivly improve the electrochemical performance of the electrode.With the sulfur content of the electrode is 1.6 mg.cm²,the first discharge specific capacity is 687.36 mAh g^-1.The fourth chapter states that C@Co_1-xNi_xS₂composite was synthesized with one-step hydrothermal method.Due to the poor conductivity of C@Co1-xNixS2,the composite is used for the host of lithium sulfur batteries,which cycle performance of the electrode is poor.