Effects Of Porous Carbon And Its Composite Structural Materials On The Electrochemical Properties Of Li-S Battery

In recent years,the popularization of electronic equipment and clean vehicles in people's lives and the intensification of non-renewable energy consumption such as oil and natural gas have placed increasing demands on the development of secondary batteries.Lithium-sulfur batteries are one of the most promising secondary batteries due to their high theoretical discharge specific capacity of 1675 m Ah?g^-1 and high energy density of 2600 m Ah?kg^-1.However,there are still several problems with lithium-sulfur batteries.The insulation nature of sulfur and Li₂S leads to low utilization of active materials;The dissolution of polysulfide and volume expansion result in shuttle effect and rapid capacity decay;The dendrite phenomenon of the anode causes the poor cycle stability poor.In order to overcome the problems of low utilization of active substances and the"shuttle effect",this paper prepared porous carbon@sulfur?HPC@S?composites and networked carbon nanotubes coated porous carbon@sulfur?CNTs/HPC@S?electrode materials to improve the electrochemical performance of lithium sulfur battery.The details are showed as follows.?1?The phenolic resin was carbonized at high temperature and then etched with KOH at 800 to prepare porous carbon materials.This experiment is mainly divided into two parts.Studying the effect of HPC@S composites prepared with different alkali-to-carbon ratios and HPC@S composites prepared by resins at different carbonization temperatures on the electrochemical performance of lithium-sulfur batteries.The results show that the HPC@S composites with with a carbonization temperature of 600 and an alkali-carbon ratio of 3 has an initial discharge specific capacity of 968.4m Ah?g^-1 at 0.1C.And the capacity is maintained at486.5m Ah?g^-1 after 300 cycles and the capacity retention rate is 50.2%,which has good cycle stability.This can be attributed to the high sulfur loading and excellent electrical conductivity of the porous carbon material.The carbon shell of porous carbon can also act as a strong physical barrier and adsorbent to inhibit polysulfide dissolution.?2?This part of the experiment is based on previous experiments,using HPC as the structural framework to study the effect of CNTs/HPC@S composite structural materials on the electrochemical performance of lithium-sulfur batteries.This composite material was obtained by coating the surface of HPC@S with different proportions of networked CNTs using the solution dispersion method.The results show that the initial discharge specific capacity of the CNTs/HPC@S-5 composites prepared when the ratio of CNTs to HPC is 5 can reach 1279.6m Ah?g^-1at 0.1C and remains 707 m Ah?g^-1 over 300 cycles with a capacity retention of 55.3%.Even at a high current density of 0.2C and 0.5 C,the discharge capacities remain at 727.8 m Ah?g^-1 and 589.1m Ah?g^-1after 150cycles,showing a good cycle stability and rate performance.Based on porous carbon as a structural skeleton,CNTs can also serve as a container for sulfur and provide connected electron transport channels.The combined effect of these two materials has played a more significant role in inhibiting the dissolution of polysulfides,while greatly improving the conductivity and utilization of S and Li₂S.