Fabrication And Properties Of Graphene/s Composites As Cathode In Lithium-ion Battery

The lithium–sulfur (Li-S) battery has been recognized as a promising high efficiencylithium-ion battery because of its high theoretical specific capacity and energydensities, low cost and toxicity. However, the lower conductivity of sulfur and thedissolution of polysulfide, generated during the discharge process, in organicelectrolyte have bad influence on cycle stability of the cell. Graphene, a one-atomlayer of graphite, possesses a unique two-dimensional (2D) structure, highconductivity and charge carrier mobility, huge specific surface area, great mechanicalstrength and low density, has showed great potential and prospect in the area ofcathode material of Li-S battery.This paper designs several graphen/sulfur composites with high sulfur content ascathode in lithium-ion battery. The morphology and structure of composites werecharacterized by FT-IR, XRD, SEM and TG, and the cycle stability was characterizedby charging and discharging at constant current. Then we the connection between thestructure and specific capacity, cycle stability has been researched.We prepared intercalated structure graphene/sulfur (HRGO/S) composite with sulfurcontent as high as77.8%via a melting method. The first cycle capacity of compositeswas660mAh/g at0.1C, but fad to425mAh/g over50cycles. The conservation rate ofcycle capacity just was61.7%. The quick decrease in capacity is mainly due to nonfully enclosed structure which leads to quick active mass loss from polysulfidedissolution.We prepared submicron sulfur enveloped by grapheme (S@RGO) particles withsulfur content as high as83.9%in alkaline GO aqueous. The first cycle capacity ofcomposites was653mAh/g at0.1C and fad to535mAh/g over50cycles. And theconservation rate of cycle capacity was increased to81.9%. The totally encapsulatedstructure by graphene had impose restrictions on the dissolution and diffusion oflong-chain polysulfide.We first prepared stable sulfur particles coated with polymer with the help ofsurfactant and then encapsulated by graphene to obtain S@PEG@RGO compositeswith sulfur content as high as77.8%. The first cycle capacity of composites was 546mAh/g at0.1C but only fad to516mAh/g over50cycles, and theconservation rate of cycle capacity was increased to94.5%at0.1C. Even more, itkept88.5%(508mAh/g) discharge capacity over150cycles at0.2C. Although theinsulative polymer lower the utilization efficiency of sulfur, but help keep betterrestrictions on the dissolution of long-chain polysulfide and structure stability, andenhance the cycle stability of cell.