超级电容器用活性炭电极材料制备及性能研究

【作者】 宋海申；

【导师】 李劼； 李荐；

【作者基本信息】 中南大学 ， 电化学工程， 2007， 硕士

【摘要】 超级电容器是介于传统电容器和二次电池之间的新型储能器件。具有高功率密度、高能量密度、循环寿命长等优点，在移动通讯、信息技术、消费电子、航空航天等领域具有广阔的应用前景，并引起了世界各国的广泛关注。目前，对超级电容器的研究主要集中在对高性能电极材料的制备上。本文选定廉价的煤焦油沥青为原料，采用预碳化工艺制备中间相沥青，并通过化学活化和物理化学联合活化制备超级电容器用电极材料；结合多种材料研究测试方法和电化学研究手段，系统地研究了相关工艺技术条件对活性炭材料比表面积、孔隙结构和电化学性能的影响；以自制活性炭材料为原料，组装了2.5V／14F的超级电容器单元，系统考察了器件的充放电特性、循环伏安特性、容量、内阻、循环性能和高低温特性等。主要结论如下：（1）中间相沥青调制温度从350℃提高到500℃，采用化学活化（碱碳比4：1，活化温度800℃）制备的活性炭比表面积先增加随后减小，在450℃调制温度下具有最大值，达3250 m²／g。活性炭质量比电容量随着调制温度的提高逐渐增大，在500℃调制温度下具有最大值，达到了123F／g。（2）碱炭比从2：1增加到5：1，在活化温度为700℃条件下制备的活性炭比表面积、总孔容、微孔孔容都显著增大，比表面积在碱炭比为5：1时具有最大值3190m²／g；中孔孔容和中孔率随碱炭比的增加先增大后减小，在4：1时具有最大值0.1753cm³／g和11.96％。在比表面积相差不大的情况下，活性炭比电容量同中孔含量具有相同的变化趋势，并在碱炭比4：1时具有最大值122.64F／g；活性炭内阻与中孔率具有相反的增加趋势，随中孔率的增加而减小。（3）活化温度从700℃提高到1000℃，在碱碳比为2：1条件下制备的活性炭比表面积和微孔孔容先增大后减小，活化温度800℃时分别达到最大值1836m²／g和0.755cm³／g；活化温度在800℃以上时，随着活化温度的升高，活性炭中孔含量急剧增加，活化温度1000℃时制备的活性炭中孔率达到29.75％。在不同活化温度下，活性炭比电容量基本上同比表面积有相同的变化趋势，但是，也较多地受到中孔含量的影响。（4）随着物理—化学联合活化碱碳比从0.5：1增加到4：1，制备的活性炭比表面积、总孔容和中孔孔容都急剧上升。当碱碳比从3增加到4时，由于生成的K₂CO₃对前驱体表面的完全覆盖，阻止了CO₂的烧蚀，防止了微孔的坍塌，致使活性炭比表面积有了显著的增大。随着联合活化的进行，活性炭中微孔的产生和扩孔作用同时进行，使得活性炭比表面积、总孔容、中孔孔容和中孔率都呈上升趋势。采用联合活化后，活性炭比表面积和总孔容没有大的变化，但是其中孔孔容和中孔率相比化学活化却有了较大幅度的提高，特别是在碱碳比较小的情况下，提高得更加明显。（5）以自制活性碳为电极材料制备的卷绕式超级电容器，外壳尺寸为φ12.5×28mm，在（C₂H₅）₄NBF₄／PC电解液中电容为14.7F，内阻为60mΩ。超级电容器单元在0.2-1.6A的放电电流下容量基本保持不变，表现出理想的大倍率放电特性，在1.6A的放电电流时，能量密度为2.96Wh／kg，在恒压一小时后，电容器漏电流小于0.5mA，在5000次循环后，超级电容器容量与500次循环时相比，衰减量小于3％。表现出良好的温度特性，能在在-40℃-70℃的温度范围内正常工作，电容器容量随温度升高而升高，在低温时，超级电容器的内阻较大。更多还原

【Abstract】 Supercapacitors have been recognized as unique energy storage devices that fillthe gap between conventional dielectric capacitors and rechargeable batteries. Assupercapacitors have the advantages of high power density, high energy density andlong cycle life, they have been used widely in the fields such as mobiletelecommunication, information technology, consumer electronics, aviation andaerospace and so on, and have been attraction more and more attention throughout theworld. Nowadays, studies on supercapacitors are mainly focused on the preparation ofhigh performance electrode material. With coal-tar pitch as raw material, mesophasepitches were produced at different temperatures, and ultra-high surface area activatedcarbons for supercapacitors were prepared by chemical activation and simultaneouslychem-physical activation. By investigating various electrochemical and materialmethods, this dissertation has investigated the influences of the process on the specificsurface area, pore structure and electrochemical properties of the activated carbons.Finally, 2.5V/14F supercapacitor was prepared and prepared activated carbon was used aselectrode materials to fabricate the carbon-based supercapacitor. The charge and dischargebehaviors, the properties of cyclic voltammetry, specific capacitance, equivalent serials resistance（ESR）, cycle properties, and temperature properties of prepared supercapacitor were all examinedin detail. The main results are as follows:（1） The specific surface area of activated carbons （chemical ratio 4:1, activatedtemperature 800℃） increased and then decreased with the increasing of modificatedtemperature from 350℃to 500℃, and the maximum surface area of activated carbonis 3250m²/g, which is obtained at 450℃. The specific capacitance of the activatedcarbons increase with temperature, and maximum value of 123F/g is obtained at500℃.（2） In chemical activation process, when activation temperature is kept at 700℃,with increasing chemical ratio from 2:1 to 5:1, the surface area and micropore volumeincrease, and the maximum surface area is 3190m²/g. The mesopore volume and ratioof mesopores increase with increasing chemical ratio from 2:1 to 4:1, and thendecrease when further increase to 5:1, the maximum value are 0.1753cm³/g and11.96%. The specific capacitance of carbons has the same tendency with mesoporevolume, and maximum value of 122.64F/g is obtained at 4:1. The resistance ofcarbons has the opposite tendency with mesopore volume. （3） In chemical activation process, when chemical ratio is kept at 700℃, withtemperature increasing from 700℃to 800℃, the surface area and micropore volumeof activated carbon increase, and both decrease with further increasing thetemperature to 1000℃. The maximum surface area of 1836m²/g is attained at 800℃,and the maximum specific capacitance of 87F/g is also attained at 800℃. The ratio ofmesopore is as high as 29.75% when prepared at 1000℃. Surface area and mesoporevolume are both important factors to affect the capacitance of activated carbons, andthe maximum capacitance is attained from the activated carbon which has the relativehigher surface area and mesopore volume.（4） In chem-physical activation process, the surface area, pore volume andmesopore volume increase with increasing the chemical ratio from 0.5:1 to 4:1. Whenthe chemical ratio increases from 3 to 4, because of the complete coverage of K₂CO₃preventing the micropore from burnt by the attack of CO₂, the surface increasesrapidly. With the progress of activation, the development of micropore and wideningof micropore appear simultaneously, so the surface area, pore volume, mesoporevolume and ratio of mesopore increase. Compared with chemical activation, theactivated carbons prepared with chem-physical method have no obvious differences insurface, but the mesopore volume and ratio of mesopore increase a lot, especially atlow chemical ratio.（5） With the prepared carbon as electrode material, the cylinder supercapacitor isprepared, and the size of case isφ12.5×28mm, the capacitance of supercapacitor is14.7F in the electrolyte of（C₂H₅）₄NBF₄/PC, and ESR is 60mΩ. In the current rangingfrom 0.2 to 1.6A, pitch carbon supercapacitor shows ideal power discharge behavior,and its capacitance is almost unchanged, the energy density of this supercapacitor is2.96Wh/kg at the current of 1.6A. The current leakage is less than 0.2mA afterkeeping stable voltage of 2.5V for 1h. After 5000 times cycles, the capacitance decayis less than 3%, compared with the capacitance of 500th cycle. The preparedsupercapacitor shows ideal temperature properties, which can be operated at thetemperature range of-40℃～70℃. The capacitance of supercapacitor may increasewith the increase of temperature, and the ESR is relatively high at low temperature.更多还原