摘要
超级电容器是一种高功率、长寿命、但能量密度较低的新型储能器件。提高能量密度最有效的方法是提高超级电容器的工作电压和电极材料的电容。由于离子液体电化学稳定窗口宽,因此采用离子液体作电解液,可有效扩宽超级电容器的工作电压,显著提高超级电容器的能量密度。根据离子液体粘度高、离子尺寸大的特点,采用较大孔径的电极材料将有利于离子移动和电子传输。炭气凝胶具有丰富的中孔,是一种具有应用前景的电极材料。本论文采用不同方法合成一系列具有不同孔结构的炭气凝胶,通过循环伏安法、交流阻抗法对其在1-乙基-3-甲基咪唑四氟硼酸盐离子液体中的电化学性能进行表征,探讨孔结构与电化学性能之间的关系。主要进行以下方面的工作：
以间苯二酚和甲醛为碳源,分别采用两种方法制备具有不同微孔／中孔面积比的炭气凝胶：1)以硅溶胶为模板,通过改变二氧化硅与炭源的质量比；2)通过改变间苯二酚与催化剂碳酸钠的摩尔比,合成炭气凝胶。将制备的炭气凝胶作为电极材料制成电极,用循环伏安法测定其在离子液体中的电容。结果发现：当微孔与中孔面积比为0.2-2.0时,电容与中孔面积比和微孔与中孔面积比之间成线性关系,并得到单位微孔面积电容和单位中孔面积电容,分别为14.2μFcm-2、5.2μf cm-2。
以间苯二酚和甲醛为碳源,添加阳离子表面活性剂十六烷基三甲基溴化铵(CTAB),分别以水、乙醇溶液为溶剂,合成不同孔径范围的炭气凝胶。采用红外光谱、扫描电镜和氮吸附对材料的微观结构进行表征,并采用循环伏安和交流阻抗对材料的电化学性能进行表征。结果发现：以水为溶剂合成,加入CTAB制得的材料由中孔结构变成微孔结构；以乙醇溶液为溶剂合成,加入CTAB制备的材料孔结构的变化则与前者相反。比表面积为549 cm2 g-1的中孔材料与比表面积为515 cm2 g-1的微孔材料相比,电容值：中孔材料>微孔材料,在较低频率范围内阻抗的模：中孔材料<微孔材料,电流与电压的相位差：中孔材料<微孔材料。结果表明：比表面积接近的中孔材料和微孔材料,电化学性能中孔材料优于微孔材料,并初步推测表面活性剂在合成过程中的作用。
Supercapacitor, as a new energy storage device, is characterized by high power and long-life. However, the energy density of supercapacitor is still low. It is efficient to obtain maximum energy density by increasing electrode capacitance and widening maximum operating voltage. The use of ionic liquid electrolyte is one of the promising strategies to widen the electrochemical stability windows of supercapacitor. Carbon xerogels with high and tunable mesoporosity as the electrode seem to be suitable for IL-based supercapacitors because relatively large ionic sizes and high viscosity of IL need more mesoporosity to move ions easily. In this work, a series of carbon xerogels with different pore structures were prepared using different methods, and its the electrochemical performance in 1-ethyl-3-methylimidazolium tetrafluoroborate electrolyte by cyclic voltammetry (CV) and AC impedance was investigated, and to explore the relation between double layer capacitance and porous structure of carbon xerogels. The main work is shown as follows:
A series of carbon xerogels with different ratio of micropore surface to mesopore surface area were prepared with resorcinol (R) and formaldehyde (F) by two methods. One is synthesized using silica sol as the template with different mass percentage of SiO2 to the total mass of R and F. Another method is synthesized with different molar ratio of R to Na2CO3. The capacitance was determined by CV method. The results show that the ratio of capacitance to mesopore surface areas has a linear relation with the ratio of micropore to mesopore surface area in the range of micropore/mesopore surface ratio from 0.2 to 2.0. The capacitance per unit micropore surface area and the capacitance per unit mesopore surface area were obtained from the linear relation.
A series of carbon xerogels with different pore size distribution are prepared using R and F as carbon precursor, adding cetyltrimethylamonium bromide (cationic surfactant), selecting water or ethanol solution as solvent. The microstructure of carbon xerogels was studied by IR, SEM and nitrogen adsorption. The electrochemical behavior was characterized by CV and AC impedance. It was found that the mesopore material with a BET surface area of 549 cm2 g"1 shows better electrochemical performance than the micropore material with a BET surface area of 515 cm2 g-1. And the role of surfactant in the process is discussed.
引文
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