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能量密度较低是双电层超级电容器急需突破的瓶颈问题之一，材料/电解液的表界面作为离子吸附以及储存能量的场所，其特性对超级电容器的比电容具有重要影响。本文通过向离子液体和水系电解液中加入不同的有机添加剂，研究有机添加剂对固-液表界面润湿性以及界面离子浓度分布等的影响，揭示了有机添加剂对超级电容器比电容和能量密度的影响及机制。取得主要结论如下：（1）针对离子液体电解液黏度高、润湿性差的问题，采用添加乙腈来提高表界面的润湿性。结果表明当离子液体[EMIM]BF4与乙腈的体积比达到1:3时，界面的接触角从43°降低到15°，润湿性的大幅提高导致材料的比表面积利用率增加，材料的比电容从12.1 F/cm3增加到29.4 F/cm3。 （2）在水系电解液中，研究了异丙醇对超级电容器比电容和能量密度的影响。发现异丙醇的加入不仅可以提高活性炭界面的润湿性，同时还有效的提高了体系在长循环后的比电容保持率；20vol%的异丙醇可以明显抑制体系在高电势下的极化现象，将工作电压窗口从-0.8~0 V提高到-0.8~0.5 V，超级电容器的能量密度也从纯水体系中的7.0 Wh/kg增加到了19.4 Wh/kg；活性炭在高电流密度（10 A/g）下比电容的衰减幅度也因为异丙醇的加入得到了巨大改善，从30.3%降低到13.9%。（3）采用实验与模拟相结合的方法，揭示了电极表面离子分布对超级电容器比电容的影响及其动力学调控机制。首先研究了电解质浓度对比电容的影响，DFT模拟发现高浓度电解质导致电极表面离子呈现多层有序分布，导致比电容的升高。通过添加有机添加剂甘油来改变离子的传递速率和充电速率，发现了动力学过程对表面离子分布的影响，提出高能量密度的离子吸附模型及其动力学优化路径。;Low energy density is one of the bottleneck problems hindering the development of double layer supercapacitors. The interface of materials and electrolytes serves as the place for ion adsorption and energy storage, which has a great influence on the specific capacitance of supercapacitors. In this paper, by adding different organic solvents into the ionic liquid and the aqueous electrolyte, the effects of organic additives on the interfacial wettability and the ion concentration distribution at interface of electrode were investigated respectively. The interface characteristics were associated with the specific capacitance and energy density of supercapacitors. The main conclusions are shown in the followings:（1）High viscosity and poor wettability are the main problems of ionic liquid as the electrolyte of supercapacitors. The acetonitrile was selected in this study and added into ionic liquid [EMIM]BF4 to improve the wettability. It was showed that when the volume ratio of [EMIM]BF4 and acetonitrile was 1:3, the contact angle of interface decreased from 43° to 15°, which resulted in a good wettability and a high utilization rate of specific surface area. The specific capacitance of materials increased from 12.1 F/cm3 to 29.4 F/cm3 as a result of the addition of acetonitrile（2）The effect of isopropanol on the specific capacitance and energy density of aqueous electrolyte was investigated in this study. It was found that the addition of isopropanol not only enhanced the wettability of the interface, but also improved the specific capacitance retention after long-term cycles effectively. In addition, 20vol% addition of isopropanol inhibited the polarization at high potential significantly, which increased the voltage window from -0.8~0 V to -0.8~0.5 V, leading to the energy density improved from 7.0 Wh/kg in 6 M KOH to 19.4 Wh/kg. The specific capacitance attenuation at high current density (10 A/g) was also improved greatly by the addition of isopropanol, which dropped from 30.3% to 13.9%.（3）By the experiments and simulations, the influence of ion distribution in the surface of electrode on the specific capacitance and its kinetic regulation mechanism was revealed. Firstly, the effect of aqueous electrolyte concentration on the specific capacitance was investigated. The DFT simulation revealed that there was multi-layered orderly packing of ions at the interface of electrode at the high concentration of electrolyte, which resulted in a high specific capacitance. By regulating the transport rate of ions in electrolyte and the charging rate of ions, the influence of kinetics process on the specific capacitance was investigated. A model with multi-layered adsorption of ions was proposed for a high capacitance , and the kinetic in favor of multi-layered adsorption was pointed out.
|刘桐桐. 有机添加剂对超级电容器界面特性及能量密度的影响[D]. 中国科学院大学,2019.|
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