Study On The Preparation And Electrochemiacl Properties Of Porous Carbon-based Composite Materials

The porous carbon material is the most commonly used materials inelectrochemical capacitors, the nature of which determines the energy density andpower density of electrochemical capacitors. Porous carbon contains a wide varietyof materials, such as activated carbon, mesoporous carbon, carbon nanotubes,graphene, etc. These porous carbons cover macroporous materials, mesoporousmaterials, microporous materials. Researches on these different types of carbonmaterials could help us understand the relationship between the capacitancecharacteristics and porous carbon materials’s characteristic, and provide a referencefor the preparation of porous carbon materials with more excellent performances. Inthis dissertation, activated carbon, mesoporous carbon, graphene, activated grapheneand their composite materials were prepared. And the pore structure and surfacefunctional groups of these porous carbon materials were analyzed, and theinfluencing factors of the performance for the electric double layer capacitance ofthe different carbon materials were investigated. In addition, the preparation ofsulfur/activated carbon composites and their performances in lithium-sulfur batterieswere also studied.The optimal procedures for the fabrication of electrochemical capacitors wereobtained through studying the influences of different types of current collectors andbinders on the capacitor performances. The results show that the electrochemicalcapacitors prepared with the mixed binder of CMC and SBR not only have a verylow equivalent serial resistance （ESR） in the1M （C₂H₅）₄NBF₄/PC, but also exhibita very good rate capability.By using KOH as activating agent, petroleum coke as raw material, weprepared activated carbons with high specific surface area. XPS analysis showedthat, the surface of activated carbon containing more C=O functional group afterpre-oxidation process. The specific capacitance values of without pre-oxidation andwith pre-oxidation treatment of activated carbon in1M （C₂H₅）₄NBF₄/PC can be upto150F·g^-1and180F·g^-1at the current density of50mA·g^-1. We also found that thecharge and discharge voltage range is a very important impact on the value ofspecific capacitance of these activated carbons.The sulfur/activated carbon composite material was prepared by hightemperature heat treatment. This material has a charge capacity of500mAh·g^-1anda discharge capacity of300mAh·g^-1in the lithium-sulfur battery at the first cycle,and it also has poor cycle stability. This shows that the combination of the sulfur and activated carbon is very weak, and sulfur generated lithium sulfide during thecharge-discharge process.The short rod-like SBA-15was prepared by hydrothermal reaction; we usedSBA-15as template prepared short rod-like CMK-3.This mesoporous carbonmaterials could get a specific capacitance value of53.5F·g^-1at0.2V·s^-1by cyclicvoltammetry.Activated graphene was prepared by using KOH as a reductant of grapheneoxide. The specific surface area of activated graphene reached the2193.3m2·g^-1when alkali-carbon ratio is5:1. And its specific capacitance value was up to130F·g^-1at the current density of2A·g^-1in the organic electrolyte. In addition, thethe petroleum coke and graphene was mixed innovatively by using KOH in thisartical. We prepared activated graphene/carbon microsphere composite materialswith electrochemical performance superior to activated carbon. Change ofalkali-carbon ratio can effectively adjust the hybrid carbon material’s pore sizedistribution, thus changing its electric double layer capacitor performance indifferent electrolytes.