Study On Preparation Of Porous Carbon From Peony Shell For Cathode Material Of Lithium Sulfur Battery

Biomass carbon materials are often used as energy storage materials due to their advantages of good electrical conductivity,low cost,environmental protection and renewable.In recent years,due to the development of lithium-sulfur batteries,biomass carbon materials are widely used in the cathode of lithium-sulfur batteries.Porous carbon materials with large specific surface area and good conductivity can be prepared by simple carbonization activation treatment of biomass materials,the prepared sulfur/carbon composite can enhance the conductivity of the positive electrode and alleviate the non-conductive problem of elemental sulfur and lithium sulfide,and the high pore volume and abundant pore structure can alleviate the volume expansion of sulfur and the shuttle effect of polysulfide in the reaction process.Using peony shell as carbon source,the structure of porous carbon prepared under different conditions and the effect of these structures on the cycling performance of lithium-sulfur batteries were studied.On this basis,nitrogen-doped porous carbon materials were prepared,and the effects of nitrogen doping on porous carbon pore structure and electrochemical propertywere investigated.Porous carbon was prepared from peony shell as carbon source and KOH as activator.The effects of activation temperature and alkali carbon ratio on the structure and electrochemical properties of porous carbon were investigated.The results show that if the activation temperature is too low or the amount of KOH is too small,the activation of porous carbon will be insufficient,and the specific surface area and pore volume will be too small.If the activation temperature is too high or the amount of KOH is too large,the porous carbon structure will collapse or be activated excessively and become flaky.Through SEM and BET analysis of the prepared porous carbon,the suitable activation temperature is 800?and the alkali carbon ratio is 4:1.Under these conditions,the specific surface area of the porous carbon OPC-800?OPC-1:4?was 1896 m²·g^-1 and the pore volume was 0.936 cm³·g^-1.The initial specific capacity of OPC-800/S was 792.2 m A·h·g^-1 at 0.2 C and retained458.6 m A·h·g^-1 after 200 cycles.Urea was used as the nitrogen source and impregnated with KOH and precarbonized peony shell,and nitrogen-doped porous carbon was prepared by activation of the mixture.The amount of nitrogen doping was controlled by controlling the ratio of urea.With the increase of the ratio of urea,the nitrogen content in porous carbon increased gradually,but the specific surface area of porous carbon increased first and then decreased.The nitrogen doping amount of NOPC-2 is1.26%,with the highest specific surface area(3177 m²·g^-1)and the largest pore volume(1.994 cm³·g^-1),and the mesoporous proportion is up to 31%.The sulfur content of the prepared carbon/sulfur composite material NOPC-2/S is up to 70.1%,and the sulfur surface load on the prepared polar sheet is about 1.6 mgcm^-2.At such a high surface load,NOPC-2/S shows excellent electrochemical performance.The initial capacity was 931.2 m A·h·g^-1 at 0.2 C,and there was 618.4 m A·h·g^-1 after200 cycles,the coulombic efficiency was about 100%,and the capacity was reserved at 66.4%.The initial capacity was 590.8 m A·h·g^-1 at 1 C,and there was 449.3m A·h·g^-1 after 400 cycles,the coulombic efficiency was about 100%,and the capacity retention rate was up to 76%.In this paper,a new idea is provided for the preparation of a positive sulfur material for a biomass based lithium sulfur battery.The porous carbon of peony shell shows excellent electrochemical properties and has the potential of practical application.