Preparation And Electrochemical Performance Of High-performance Activated Pitch Based Carbon Fiber

Supercapacitor has not only higher energy density than conventional capacitors,but also much higher power density than batteries.Supercapacitor is a promising energy storage device.Electrode material is one of key factors influencing the performances of supercapacitor.Therefore,the researched and developments of electrode materials have become the hot topics in the recent years.In this dissertation,the preparation,structural modification and supercapacitive performances of pitch-based activated carbon fibers were systematically investigated.We focus on investigation the effects of activated conditions on the structure and electrochemical performances of ACFs and modification by heat treatment and metal doping to improve the supercapacitive performance.The results are as follows:?1?Microporous activated carbon fibers?ACFs?with high surface area and high yield were successfully prepared by chemical etching using mesophase pitch-based carbon fibers?CFs?as raw materials and KOH as a activating agent.The activation was carried out under low temperature and short activation time.The effects of activation temperature,activation time and the mass ratio of KOH/CFs on the morphology,degree of crystallinity,surface structure,pore structure,and supercapacitive performances were systematically investigated.The results showed that the optimal reaction conditions were KOH/CFs mass ratio of 4/1,the activation temperature of 550°C,and activation time of 1 h.The as prepared electrode materials showed a ultra-high capacitance up to 426.6 F g^-1 at 0.1 A g^-1 in 6 M KOH aqueous electrolytes,which is higher than most of the reported carbon materials.Furthermore,they manifest excellent cycle stability(391.3 F g^-1 after 1000 cycles,91.9%capacitance retention).?2?In order to improve the degree of crystallinity of the ACFs,the as-prepared carbon fiber were modified by carbonization.The effects of carbonization temperature on the morphology,crystallinity,pore structure and supercapacitive performances as the electrode material of the supercapacitor were systematically investigated.The results showed that the ACFs electrodes carbonized at 1200°C?ACFs-1200?had higher conductivity,higher specific capacity at high current density and cycle stability than the non-carbonized ACFs electrodes.The ACFs-1200 electrodes exhibited excellent electrochemical performance with a specific capacity up to 204.2 F·g^-1 at 0.1A·g^-1;a higher specific capacity of 148.6 F·g^-1 than the non-carbonized ACFs at 20A·g^-1;low impedance(R_ct,0.25?;R_s,1.41?);and excellent cycling stability?97.0%after 1000 cycles?in 6 M KOH aqueous solution.esoporous.?3?Based on the analysis of the structure characteristics of carbonized graphitized activated carbon fibers,the as-prepared ACFs were modified by in-situ nickel catalytic graphitization of carbon.The results show that the high graphitization can be achieved at a lower temperature after metal catalysis than the non-catalyticed ACFs electrodes.The ACFs catalytic graphitizated at 900°C had higher conductivity,higher specific capacity at high current density than the other temperature treated ACFs electrodes.