Preparation Of Nanometer Carbon Sphere/Sulfur Complex And Its Application In Lithium Sulfur Battery

Lithium-sulfur batteries are considered to be one of the most promising options for the next generation of rechargeable batteries due to higher theoretical energy density and lower cost.However,the practical application of lithium-sulfur batteries is severely hampered by polysulfide dissolution and sulfur intrinsic insulation.Therefore,this paper studies a new strategy to solve the above problems of lithium sulfur battery,which are mainly carried out in the following contents:First,based on the current research status of carbon/sulfur composite materials for lithium sulfur batteries,it is found that carbon sphere materials have good conductivity,adjustable size and large pore area,and can be used as a good host material for sulfur positive electrode.The reagents and instruments required in the experiment and the characterization methods and testing methods required during the research process are described.Then,a cobalt-nitrogen co-doped hollow carbon sphere?Co,N@CPDA-HCS?is designed and synthesized,whose carbon shell is highly conductive to contain sulfur.In this unique material architecture,the highly conductive shell carbon can provide a fast electron conduction paths and structural stability.The superfine Co nanoparticles uniformly embedded in the carbon shell can accelerate the conversion kinetics of the polysulfides by strong chemical interaction.Moreover,the hollow structure provides a buffer space for the volume change of sulfur during charging and discharging,thus leading to a good cycle stability of sulfur cathodes.The Co,N@CPDA-HCS exhibits balanced high electrochemical performance with respect to specific capacity,rate capability,and cycling stability.Specifically,the S/Co,N@CPDA-HCS presents a high initial gravimetric capacity of 1365 m Ah·g^-1at 0.1 A·g^-1.The discharge capacity of 588 m Ah·g^-1still remained at the current density of 1 A·g^-1after 300 cycles.In addition,a carefully designed hollow carbon sphere frame?S/Fe₃O₄-NC?is reported here as an efficient sulfur carrier for lithium-sulfur batteries.In this unique hollow carbon sphere framework,the strong chemical interaction between polar Fe₃O₄nanoparticles and nitrogen-carbon binds the active substance,inhibits the diffusion of polysulfide intermediates,and promotes rapid electron/ion transport.Moreover,hollow carbon spheres improve electrical conductivity and serve as a buffer layer to accommodate volume changes during charging/discharging.With this advantage,the S/Fe₃O₄-NC cathode exhibits high initial discharge capacity(1461m Ah·g^-1at 0.1 A·g^-1),excellent rate performance(636 m Ah·g^-1at 2 A·g^-1)and long cycle stability(the capacity decay of each cycle only is 0.08%after 500 cycles at 1A·g^-1).Finally,the work in this thesis is summarized,and the future development of lithium sulfur batteries hollow carbon sphere composite cathode materials is prospected.