Synthesis And Application Of Carbon-based Materials In Lithium-sulfur Batteries

Li-S battery is one of the most promising candidates due to its high theoretical capacity and energy density of 1675 mAh g^-1 and 2600 Wh kg^-1,respectively.In addition,the natural sulfur has advantages of abundant,non-toxic,environmental friendliness and low price,so Li-S batteries have become a research focus in electrochemical energy storage with broad application prospects.But its poor electrical conductivity and shuttle effect seriously affects the development of Li-S battery.Due to its high conductivity and the diversity of nanometer structure,biomass-derived carbon based materials as sulfur host have attracted much attention in the application of lithium sulfur batteries.The research in this thesis mainly centered on the high-stable carbon/sulfur composite cathodes,designing the preparation of the cheap green and heteroatom doping carbon-derived materials as the host of sulfur,which can improve the electrochemical performance of lithium sulfur batteries via effectively suppressing the shuttle effect.The main contents and results are summarized as follows:In this paper,we have designed and prepared a series of coralline-like hierarchically porous carbon materials with nitrogen,oxygen co-doped and high specific surface area as the host matrix for improving cycling stability in Li-S battery.The hierarchically porous carbon materials were made by hydrothermal carbonization and activation of enteromorpha.The raw material is rich who belongs to marine waste pollution,the preparation method is simple,economic and environmental protective.The CNHPC/S composite exhibits an initial discharge capacity of 1555 mAh g^-1?93% of theoretical capacity?at 0.1 C and a capacity loss of 0.05% per charge-discharge cycle after 500 cycles at 0.5 C with a stable coulombic efficiency of 100%.The improved electronic conductivity and the adsorption of polysulfides due to physical confinement of porous structure and itself rich nitrogen?oxygen co-doping,effectively restrains shuttle effect,further enhances good electrochemical activity.We have designed and prepared a series of tremella-like hierarchically microporous carbon materials with high nitrogen,oxygen and fluorine co-doped and high specific surface area as the host matrix for improving cycling stability in Li-S battery.The microporous carbon was made by hydrothermal carbonization and activation of fly larvae.The activation and pickling of sample during the preparation process is optimized to ensure that the samples can be mixed well and improve the purity of sample.The raw material that is fly larvae are abundant in nature and are one of the four pests,its synthesis is facile and reasonable.The TNMC300/40%S exhibits a high discharge capacity of 851.2 mAh g^-1 at 0.1 C after 100 cycles.Under different current density,all TNMCs show high coulomb efficiency that is close to 100%,and average capacity loss of per cycle is below 0.05%.Pure micropores can well confine more polysulfides,itself inherent rich nitrogen,oxygen and fluorine improved the electrical conductivity of the composite materials,suppressed the migration and diffusion of polysulfides,and reduced the loss of active materials,further improved the cycling stability and high capacity.