Preparation And Electrochemical Properties Study Of Cathode Materials For High-performance Lithium-sulfur Battery

Lithium sulfur is novel secondary energy storage batteries,and the specific capacity of sulfur cathode can reach 1675.0 mAh/g.Besides elemental sulfur is of great advantages,including low price,and non-toxic,attracting considerable researches and attention.Despite lithium sulfur batteries have many advantages,there are still some obstacles to its commercial application,including the low electrical conductivity of sulfur,severe capacity degradation at large current,and the shuttle effect of polysulfide.Aiming at the existing problems of lithium sulfur battery cathode material,we prepared and studied three different structures of sulfur-carbon composite material in order to store sulfur,limit sulfur,and immobilize sulfur,our main research contents as follows:(1)Sulfur-impregnated hollow carbon sphere composite was prepared as the cathode material for lithium sulfur batteries.The morphology,composition,and structure of the as-synthesized composite were characterized by Scanning Electron Microscopy(SEM),X-ray diffraction(XRD),and the Transmission Electron Microscopy(TEM)technique.It was found that uniform mono-dispersive hollow carbon sphere can be synthesized by the template method combined with chemical polymerization.The diameter of the sphere is about 450 nm and the thickness of its wall is about 25 nm.Furthermore,sulfur-impregnated hollow carbon sphere composite can be achieved by the melting-diffusion method.The mass loading of sulfur is 2.67 mg/cm~2.The electrochemical performance of the as-synthesized composite as a cathode material for lithium sulfur batteries was also investigated.The results indicate that the specific capacity can reach 1285.0 mAh/g,and it can even keep 756.2 mAh/g after 500 cycles.(2)We prepared a novel tube-in-tube structured carbon nanomaterial(TTCN)as the host for sulfur cathode.MWNTs were encapsulated into hollow porous carbon nanotubes,S-TTCN composite can be obtained by melting-diffusion method.The mass loading of sulfur is 2.4 mg/cm~2.The electrochemical performance of the as-synthesized composite as cathode material for lithium sulfur batteries was also investigated.The results indicate that the specific capacity can reach 1464.7 mAh/g,and even in 0.5 C current density,the specific capacity can keep 581.7 mAh/g.(3)Flexible lithium sulfur cathode material composed of graphene-carbon nanotube-Poly-diallyldimethylammonium chloride-sulfur(G-CNT-PDDA-S)was synthesized by the method of vacuum filtration.The results show that the solution method can effectively improve the phenomena of agglomeration and overlap of the nanomaterials,and the sulfur in the cathode electrode membrane is uniform.The mass loading of sulfur is 2.14 mg/cm~2After the electrochemical performance test,the initial discharge capacity could reach1280.1 mAh/g,and the capacity retention rate was 58.8%after 500 cycles.