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Preparation And Application Of High Performance Activated Carbon Electrode Materials

Posted on:2009-01-29Degree:MasterType:Thesis
Country:ChinaCandidate:J YangFull Text:PDF
GTID:2132360242478371Subject:Physical chemistry
Abstract/Summary:PDF Full Text Request
Supercapacitor,also named as electrichemical capacitor,is a new kind of energy storage device in-between conventional capacitor and second battery.It has been widely applied in military and electronic products or equipments.The electrode is an important component influencing the performance of supercapacitor.Therefore,the research on high performance electrode materials has been hot topic in this filed. Carbon electrode materials have attracted great attention to academe and industry, because of their abundant sources,commercial available,low price,excellently physical and chemical stability and feasibility of manufacture.The purpose of this study is to prepare low cost and high performance carbon electrode material for supercapacitor and to study the relation between carbon property and performance of the carbon electrode base supercapacitor.The nitrogen adsorption was used to study the specific surface area,pore volume,average pore diameter and pore size distributions.The properties of supercapacitors,such as specific capacity,equivalent series resistance(ESR),leakage current were studied by electrochemical methods of cyclic-voltammetry,constant current charge/discharge, alternating current impedance etc.Main investigations and achievements were discribed as following:Activated carbon samples were prepared by means of simultaneous ZnCl2-CO2 physical-chemical activation using walnut shell as precursor.The specific surface area,pore size distribution was studied according to the nitrogen adsorprion-desorption isotherms by using BET model,t-plot and BJH method.The influence of ZnCl2/shell ratio,activation temperature,activation time and CO2 gas flow on the specific surface area and porosity parameters of activated carbon was studied through designed orthogonal experiments.The resurt showed that ZnCl2/shell ratio and activation temperature are two key factors influencing the porosity of activated carbon.By optimizing activation conditions,the specific surface area and pore volume of resultant AC could be as high as 2266 m2/g,1.4169 cm3/g;and the average pore size of another sample could reach to 2.73 nm with a medium specific surface area of 1206 m2/g.The sandiwich-type supercapacitors were assembled with resultant carbon electrodes and electrolyte of 6 mol/L KOH solution.Their electrochemical properties were investigated by charge-discharge of constant current,cyclic voltammogram etc. The results demonstrated that pore structure,especially the pore size distribution had a significant inference on the performance of supercapacitors.For KOH electrolyte solution,the pore size distribution in the range of 1.5 nm-4 nm is favorable to the formation of electric double layer on the carbon surface.And the surface functional groups can improve the wettability and generate pseudocapacitance,so that enhanced the specific capacitance of carbon electrode.The specific capacitance increased proportional with increasing microporous and BET surface area of AC with an advange pore size arround 2 nm.Compared with a commerical AC,the resultan ACs prepared showed higher ratio of effective surface area for the formation of electric double layer and better electrochemical performance.The specific capacitance could be as high as 292 F/g at 5 mA change/discharge current;and retained a high value of 210 F/g at 80 mA.The resistance and leakage current of the capacitor are 0.57Ωand 0.19 mA,respectively; the energy density,power density and maximum power of capacitor were 7.3 Wh/kg, 770 W/kg and 5.1 W/g,respectively.The capacitance maintained above 90%after 1000-cycle charge-discharge.NiOx/AC composite electrode materials were prepared by means of sol-gel method and characterized by the nitrogen adsorption,XRD,TGA.And the performance of electrode of composite material was also tested.The results showed that the performance and specific capacitance of the composite electrode were improved compared to the blank AC.The composite materials were thermally treated at different temperature.The result showed that the specific capacitance of composite material treated at 320℃could be as high as 235.2 F/g,87.4%higher than of original carbon.The corresponding volume specific capacity is 131.3F/cm3, 80.1%higher than of original carbon.The capacitors with composite carbon electrodes exhibited much better performance in terms of electrochemical stability, cyclic voltammogram,charge-discharge,impedence spectrum and leakage current.In order to increase the energy and power density,the organic electrolyte Et4NBF4/PC instead of KOH solution was used in the carbon-based supercapacitors. The specific capacitance of a lab-made mesoporous carbon sample was 182 F/g at the discharge current of 5 mA;the corresponding energy density attain to 39.5Wh/kg. The highest power density could be 2583.5W/kg.
Keywords/Search Tags:Activated carbon, Functional group, Composite carbon electrode, Electrichemical capacitor, Organic electrlyte
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