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Preparation And Electrochemical Performance Of Electrode Material For Supercapacitors

Posted on:2019-04-24Degree:MasterType:Thesis
Country:ChinaCandidate:Q LuFull Text:PDF
GTID:2382330548481792Subject:Chemistry
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Supercapacitors,also called electrochemical capacitors or ultracapacitors,have attracted significant attention from both industry and academia due to its high power density,rapid charge/discharge rate,long cycle life,green environmental protection etc.However,the low energy density of supercapacitors greatly limits its application.Therefore,how to improve the energy density of supercapacitors and maintain the advantages of supercapacitors has become a research hotspot.As we all know,the energy density of supercapacitors is mainly determined by the capacity of electrode materials and the voltage window of capacitor.There are various types of electrode materials,such as carbon materials,metal oxide and conducting polymer etc.Among them,carbon materials have been widely used,which have many advantages of the abundant source,large surface area,developed pore structure,low price,environment ·friendly,good stability and excellent conductivity.Nevertheless,the low specific capacitance of carbon materials cannot satisfy the practical application for demand of the high energy density of supercapacitors.The metal oxide and conductive polymers have high theoretical specific capacity,but their stability,conductivity or cycle performance is too poor.They just evade the advantages of supercapacitor.Based on the above considerations,composite materials are prepared to be assembled into a high performance supercapacitor in order to make full use of the advantages of different materials and combined with the characteristics of different materials.These composites include carbon/metal compound composite,carbon/conductive polymer composite,conductive polymer/metal compound composite.In this paper,the hollow carbon microsphere@polypyrrole(HCS@PPy)composite has been designed and synthesized through in situ chemical oxidation polymerization using TEOS as template and phenolic resin as a carbon source.The physical and electrochemical properties of HCS@PPy composite are further studied.Besides,the manganese dioxide/three-dimensional ant-nest-like hierarchical porous carbon composite(MnO2/ANHPC)is successfully prepared and its physical and electrochemical properties are studied.In addition,to further optimize the performance of supercapacitor and increase the energy density of supercapacitor,hybrid lithium ion capacitor successfully assembled employ biomass derived porous carbon cathode material and silicon/flake graphite/carbon(Si/FG/C)nanocomposite as anode material.Its electrochemical performance was studied and obtained a series of meaningful results.The main work in this thesis are as follows:(1)Ant-nest-like three-dimensional hierarchical porous carbon(ANHPC)is successfully prepared via KOH chemical shearing using the fullerene as carbon source.Afterwards,MnO2/ANHPC is successfully synthesized through redox reaction of the KMnO4 solution with porous carbon.The results show that the specific surface area of MnO2/ANHPC composite is up to 543 m2 g-1,and the average pore size is 7.21 nm.The specific capacitance is up to 662 F g-1 at the current density of 1 A g"1.Besides,the capacity retention rate of symmetric supercapacitor based on the MnO2/ANHPC composite is up to 93.4%after 5000 cycles.In addition,the maximum energy density is 21.5 Wh kg-1 at the power density of 250 W kg-1,while its power density is still at 14.5 Wh kg-1 when the power density is 5000 W kg-1.(2)Hollow porous carbon microspheres(HCS)are synthesized using phenol formaldehyde resin as carbon source and tetraethyl orthosilicate as template.A conductive polymer polypyrrole(PPy)is coated on the surface of HCS by chemical in situ polymerization.The results show that the HCS@PPy composite is composed of interconnected mesoporous/microporous shells,developed internal pore structure and hollow macroporous structures,which is conducive to the rapid transmission of electrolyte ions.The specific capacitance of HCS@PPy composite is up to 508 F g'1 at the current density of 1 A g-1.Furthermore,asymmetrical supercapacitor assembled by HCS as the positive electrode and HCS@PPy composite as negative electrode shows a high energy density of 46 Wh kg-1 at 350 W kg-1,even at the high power density of 5600 W kg-1,its energy density still remains at 19.6 Wh kg-1.(3)The Chinese-chives derived porous activated carbon(CPAC)is prepared by a two-step process using Chinese-chives as carbon source and KOH as activator,and the influence of activation ratio on its physical and electrochemical properties are discussed.As a result,the result shows that when the mass ratio of activated carbon to KOH is 1:5,CPAC-5 possesses the largest specific surface area of 3011 m2 g-1 and average pore size of 2.77 nm.The specific capacity of CPAC-5 is up to 135 mAh g-1 at the current density of 0.3 A g-1,and the capacity retention rate remains at 94%after 2000 cycles.Subsequently,hybrid lithium ion capacitor(Si/FG/C//CPAC)is successfully assembled using the active porous carbon as cathode materials and Si/FG/C as anode material,which can be charged/discharged at an operating voltage of 2-4.5 V.Si/FG/C//CPAC hybrid system exhibits a high energy density of 159 Wh kg-1 at 945 W kg-1.Furthermore,the capacity retention rate of the hybrid system is 80%after 8000 cycles and the the coulombic efficiency is almost 100%.
Keywords/Search Tags:Supercapacitor, Porous carbon, Composite materials, biomass, Lithium-ion supercapacitor
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