Preparation?Modification And Electrochemical Performance Of Peanut Shell-Based Carbon/Surful Composite Materials

Lithium sulfur?Li-S?batteries are considered to be the new-generation secondary batteries and have been under great attention,duing to their high theoretical energy densities(2500Whkg^-1)high theoretical capacity(1675mAhg^-1),environmental friendliness and low cost.However,as the cathode of Li-S batteries,sulfur shows lots of deficiencies,including the poor electronic conductivity,the large volume change of the sulfur cathodes during cycling,the dissolution of the reaction intermediates of polusulfides in the electrolyte and the shuttle effect,which result in poor cyclic stability and low rate capability.It is these shortcoming that limit the use of the Li-S batteries in the market.Based on a introduction of the developments of the sulfur/carbon cathode composite materials,and the characteristics of the agricultural country,the environment friendly biomass carbon,hierarchically porous carbon?HPC?is synthesized using peanut shells as carbon source,KOH as the activator and composites with sulfur for lithium-sulfur batteries.In addition,the carbon materials were modified with FeS₂,which were used as additive,and nitrogen doping,to prepare the S/HPC added by FeS₂ and S/NHPC composite materials.The main contents are as follows:1.Hierarchically porous carbons with different special surface area and pore volume are synthesized using peanut shells as carbon source and KOH as the activator by changing the dosage of KOH and carbonization temperature.The results show that the hierarchically porous carbons exhibits high electrochemical performance when the quality of KOH is 4.0g and carbonization temperature is set at 800?.Special surface area and pore volume of the porous carbons obtained are 1818.0m²g^-1 and0.920cm³g^-1.The S/C composite materials?with 30.35%sulfur loading?show an initial capacity of 1643.8 mAhg^-1 at the 0.5C,and retain capacity of 815.7mAhg^-1after 100 cycles.The improved electrochemical performance of S/HPC composite materials is attributed to the absorption of the hierarchically porous carbon to sulfur,which evidently limits the dissolution of polysulfide in the electrolyte and enhances the electron conductivity of the composite;The large pore volume reduces the volume effect of the sulfur cathode during cycling.2.Granular FeS₂ is synthesized by sulfurization method,then is added to S/C composite electrode with different dosage of annexing agent by changing the quality of FeS₂.The results show that the composite electrode exhibits high electrochemical performance when the dosage of FeS₂ is 15%.This S/HPC composite materials?with53.02%sulfur loading?show an initial capacity of 1206.7 mAhg^-1 at the 0.5C,and retain capacity of 621.4mAhg^-1 after 100 cycles.It shows that the suitable addition of FeS₂ is useful to improve the electrochemical performance and the coulomb efficiency of S/C composite materials.3.Nitrogen doped porous carbon is synthesized by adding tripolycyanamide?as a nitrogen source?to HPC following calcination treatment at high temperature.The results show that the composite electrode exhibits high electrochemical performance when the mass ratio of tripolycyanamide to HPC is 30:1.The S/NHPC composite materials?with 57.82%sulfur loading?show an initial capacity of 1298.8 mAhg^-1 at the 0.5C,and retain capacity of 595.3mAhg^-1 after 100 cycles with the high coulombic efficiency of 95%above.