Study On The Construction Of Lithium-Sulfur Battery Positive Electrode Based On Multi-dimensional Carbon Nanomaterials And Its Performance

Lithium-sulfur batteries are the most promising next-generation electrochemical energy storage device to replace lithium-ion batteries.The theoretical specific capacity of the positive electrode active material sulfur in lithium-sulfur batteries is as high as 1675mAh g^-1,and its energy density is far higher than the electrode materials of lithium-ion batteries found today,but the conductivity of sulfur and discharge products Li₂S/Li₂S₂ is poor.The"shuttle effect"caused by the dissolution of polysulfides restricts the development of lithium-sulfur batteries.Therefore,it is the key to improve the performance of lithium-sulfur batteries by designing cathode materials with novel structure and good conductivity.This paper intends to cooperate with the special structural characteristics of helical carbon tubes（HCNTs）,good dispersibility of two-dimensional graphene oxide（GO）,and good adsorption performance of carbon nanospheres（CSs）,making full use of the excellent properties and synergies of the building units It can be controlled to obtain three-dimensional wrapped nano-sulfur structure,and further improve the electrochemical performance of lithium-sulfur batteries through nitrogen doping,providing a certain technical support for the application of lithium-sulfur batteries.The details are as follows:（1）A three-dimensional network structure of reduced graphene oxide（rGO）coated HCNTs and loaded with nano-sulfur was designed and synthesized using solution self-assembly and vulcanization strategies.HCNTs and GO are easy to form a three-dimensional hole-shaped reinforced concrete structure,which is conducive to the integration of nano-sulfur into the three-dimensional hole structure and plays a role in wrapping and fixing sulfur.The addition of HCNTs can effectively prevent the stacking of GO and improve the conductivity.This special structure greatly reduces the direct contact between the polysulfide and the electrolyte,improves the nucleation/conversion redox kinetics and reduces the overpotential of the polysulfide.The results show that the specific discharge capacities of the HCNTs/rGO/S composite cathode at the first cycle of 0.1C,0.2C,0.5C can reach 1196 mAh g^-1,1130 mAh g^-1,1009 mAh g^-1,respectively.The capacity retention rates after 200 cycles are 85%,86%,and 86.5%,respectively.（2）Using hydrothermal reduction nitrogen doping method,aminated HCNTs and sulfurized GO were prepared into nitrogen-doped black hydrogel for flexible lithium-sulfur battery positive electrode.Nitrogen doping can improve the conductivity of the composite material and the adsorption capacity of polysulfides.The spiral structure in HCNTs can convert the external stress into the bending of the electrode,can provide all-round deformation without generating uneven interface stress and sliding stress,and improve its flexibility characteristics.HCNTs form a conductive network to provide fast electron/ion transmission channels.The results show that the specific discharge capacities of S/N-rGO/E-HCNTs composite cathodes at 0.1C,0.5C,1C rates can reach 1083 mAh g^-1,1051 mAh g^-1,1001 mAh g^-1,respectively.The capacity retention rates after 500 cycles are 68%,70%,and 71%,respectively.（3）Using the molting method,the mixture of HCNTs and CSs@S was prepared into a"nest egg"structure with carbon balls as the adsorption center.Among them,HCNTs shorten the diffusion path and effectively achieve fast reaction kinetics.The walls of HCNTs effectively limit the volume expansion of sulfur during discharge.CSs have excellent adsorption capacity,and nano-sulfur can be evenly dispersed into the internal cavity and stably exist.The results show that the specific discharge capacity of the HCNTs/CSs/S-3 composite positive electrode at 0.1C,0.5C,and 1C rates can reach 1085 mAh g^-1,1047 mAh g^-1,1005 mAh g^-1,respectively.The capacity retention rates at 0.1C,0.5C after 200 cycles are 81%and 88%.