Internal And External Structure Design And Performance Research Of Self-supporting Carbon Nanofibers For Lithium-sulfur Batterie

Lithium-sulfur batteries have been widely studied by domestic and foreign scholars for their high theoretical specific energy(2600 Wh Kg^-1)and bulk energy density(2800Wh L^-1).However,the insulating properties of sulfur,volume expansion,and the"shuttle effect"have prevented the commercial application of lithium-sulfur batteries.The fibers obtained by electrospinning have the advantages of nanoscale size,large specific surface area,continuity,and controllable structure,and have become a hot research topic for self-supported cathodes and interlayers for lithium-sulfur batteries.In this paper,we developed a self-supported cathode and interlayer for lithium-sulfur batteries with excellent performance based on electrostatic spun carbon nanofibers with internal and external spatial structure design to improve the electrochemical performance by improving the conductivity of the sulfur cathode and mitigating the"shuttle effect".The main research conducted is shown below:（1）Based on the"inner"strategy-design of internal pores structural of CNFs:using polyacrylonitrile（PAN）as core layer solution,PAN and polymethyl methacrylate（PMMA）mixed solution as shell solution,a core-shell nanofiber（SPCNFs）with a porous structure of the shell layer distribution was prepared by coaxial electrospinning and carbonization,and then SPCNFs@S composite cathode was prepared by solution dripping and molten sulfur loading.Then the morphology and electrochemical properties were characterized:The amorphous carbon of the core layer and the porous structure of the shell give the material good mechanical properties and limiting effect on polysulfides.The initial discharge specific capacity was 986 m Ah g^-1 at 0.2 C and still reached 499.8 m Ah g^-1 after 100 cycles.（2）Based on the"external"strategy-design of external space structure of CNFs:a three-dimensional bicontinuous CNTs-CNFs conductive network framework was prepared by electrospinning PAN,electrodeposition,and chemical vapor growth,and then the CNTs-CNFs@S composite cathode was prepared by solution dripping and molten sulfur loading,and the morphology and electrochemical properties were characterized:As an independent freestanding substrate,CNFs builds a large-scale continuous conductive network,and the tip cross-winding CNTs forms a locally fine conductive network.This three-dimensional bicontinuous structure promotes electron transport,accelerates redox kinetics,and has a good limiting effect on polysulfides.The battery with CNTs-CNFs@S as cathode has a small charge transfer impedance;the initial discharge capacity was as high as 1386.4 m Ah g^-1 at 0.2 C and 802 m Ah g^-1after100 cycles,and 607.7 m Ah g^-1after 500 cycles at 1 C,with a decay of 0.088%per cycle.（3）The three-dimensional bicontinuous CNTs-CNFs conductive network was used as both the cathode and the interlayer to construct a bilayer adsorption structure,which eased the polysulfide shuttle,accelerated the kinetics,reduced the electrode polarization,and improved the active material utilization.At 1 C,the discharge specific capacity was 426.9 m Ah g^-1 after 1000 cycles with a decay rate of 0.064%per cycle,and the coulomb efficiency was maintained above 95%;with excellent rate performance and a capacity recovery rate of 93.01%.