Green Synthesis Of High Surface Area Porous Carbon Materials And Their Application In Lithium Sulfur Battery Research

Lithium-sulfur batterie(LSB), which use earth-abundant sulfur as a cathode material, are one of the most promising candidates for next-generation rechargeable batteries due to their high theoretical energy density, cost effectiveness, and environmental friendliness. Despite the great promise of LSB, two main technical challenges must be addressed before they can find practical use: 1) the intrinsically poor electronic conductivity of sulfur; 2) the polysulfides’(PS) “shuttle” effect in organic electrolytes. It is therefore crucial to improve the conductivity of the sulfur cathode and maintain/reuse the soluble PS. In this thesis, a simple,green, facile water stream etching method is developed to obtain high surface porous carbon nanotubes(PCNTs) and porous carbon(PC), which are applied in LSB. The main contents are as follows:(1) Using water stream etching methode, the PCNTs are prepared.Researches show that the specific surface area and pore volume of the original CNTs are greatly improved after water stream etching.Furthermore, the intrinsically tubular structure of CNTs is reserved. The electrochemical performance of PCNTs-S composites is superior to that of CNTs-S composites, a capacity of 950 mAh/g is retained after 250 cycles when cycled at 0.2C.(2) Based on the PCNTs-S cathode above, an interlayer serving to intercept the migrating PS and reuse the trapped active material is inserted between the cathode and separator to obtain the PCNTs-S@graphene/TiO2 cathode simply by coating the surface of PCNTs-S cathode with a graphene/TiO2 film. The weight of graphene/TiO2 interlayer is very light, which accounts for only approximately 7.8 wt% of the whole cathode. Meanwhile, researchesshow that the modified electrodes reveal excellent cycling stability and discharge capacity compared with alternative electrodes, an ultralow capacity degradation rate of 0.01% and 0.018% per cycle is obtained,measured over 1000 cycles at 2 C and 3 C, respectively.(3) Applying biologic material chalina as a carbon precursor, PC is obtained by high temperature annealing. Then modified PC with a specific surface area of 360 m2/g is prepared by above water stream etching method. The cell is assembled after preparing the PC-S composites cathode. Electrochemical performance results show that the modified PC-S composites show higher capacity and higher cycle stability, a capacity of 450 mAh/g is retained after 500 cycles when cycled at 0.5C with 90% capacity retention.