【作者】 李文尧；

【导师】 胡俊青；

【作者基本信息】 东华大学 ， 材料物理与化学， 2014， 博士

【摘要】 近年来,超级电容器以其高功率密度、快充放电速度、长使用寿命和高安全性,逐渐成为下一代能源装置中最具潜力的储能设备,能够满足时代发展所需的现代电子设备和能源系统。根据电荷存储机理,超级电容器大致可以分成两类,即使用碳基电极材料的双电层超级电容器和使用具有氧化还原反应电极材料的赝电容超级电容器。到目前为止,对于赝电容超级电容器电极材料的研究主要集中在发展具有商用前景的过渡金属氧化物,因为它们具有丰度高、价格低廉、环境友好的特点,特别是能为氧化还原反应提供多种电荷价态,因而能够获得更高的能量密度和理论比电容值。由于不同的过渡金属氧化物有着各异的微观结构和组分,在作为电极材料时,电极／电解液界面性质和离子传输速率也不尽相同,因而电荷存储能力具有本质的差别。在这篇博士学位论文中,我们以多种不同微观结构的MnO2电极材料的制备为基础,围绕提高过渡金属氧化物电极材料电化学性能所面临的部分挑战,逐步发展Mn基复合金属氧化物电极材料,并探讨其在实际应用中的影响因素。论文中的主要内容概括如下：1采用水热法合成了长～40μm,宽～15nm的单晶α-MnO2超长纳米线。通过改变表面活性剂合成了a-MnO2纳米线和纳米棒。利用TEM-STM样品台测试了单根MnO2纳米线和纳米棒的原位电学性能,结果表明Mn02纳米线的导电性优于纳米棒,在-5-5V电压变化范围内,电流变化范围为-252.5～206.7nA,高于纳米棒(-122.3～92.3nA)。对比三种MnO2电极材料,超长纳米线的电化学性能最为优异,1A/g的电流密度下,其比电容值达到了345F/g,电流密度增大10倍时比电容仍然能保持54.7%。2采用恒电流沉积法在泡沫镍基底上生长了长约数微米,宽8-10nm的a-MnO2超细纳米带。通过改变测试温度,探讨了0℃、25℃和50℃下超细纳米带电极材料的电化学性能。发现在50℃时性能最为优异,200mA/g电流密度下比电容达到了509.5F/g,远高于0和25℃下的电容值。此外,50℃时也表现出较好的倍率性能,当扫描速度增加100倍时,能够保持初始比电容值的39.1%。通过变温下5000次的长循环稳定测试,发现MnO2超细纳米带最终仍然能够保留91.3%初始电容量,证明所制备的超细纳米带具有良好的抗温变效应。3设计并通过分步可控电沉积法将MnO2纳米片或纳米棒生长在Au包覆的C0304多孔纳米墙阵列上,形成Co3O4@Au@MnO2三维层状异质结。由于其独特的自组装结构和特征,即C0304多孔纳米墙、超薄MnO2纳米片以及夹在中间的高导电Au层,使得每一部分都为其用于能量储存提供所需的重要作用。合成的三维层状异质结电极材料具有优异的电化学性能,如高比电容(10mV/s时电容为851.4F/g,1A/g电流密度时为1532.4F/g),高倍率性能以及优异的长循环稳定性(5000圈循环测试后几乎没有衰减),因此该材料在高性能超级电容器中具有很好的应用前景。4采用水热法合成了平均直径为4-6μm的海胆状MnCo2O4.5前驱体,400℃煅烧后获得立方相MnCo2O4.5晶体。SEM和TEM表征发现其分级结构是由颗粒链接而成,使得海胆状MnCo2O4.5富含孔隙。将其作为电极材料,在5mV/s扫速下具有151.2F/g的比电容。重要的是,当电流密度增加50倍情况下,其比电容依然能保持初始的83.6%；不同电流密度充放电测试2100次后无衰减现象发生。更多还原

【Abstract】 Supercapacitors have become the most promising candidates for next-generation power devices in recent years because of their excellent properties such as high power density, fast charge-discharge rate, long cycle life and safe operation for time-dependent power needs of modern electronics and power systems. According to the charge-storage mechanism, they are generally divided into two categories, i.e., electrical double-layer capacitors using carbon-active materials, and pseudocapacitors using redox-active materials. Up to now, for pseudocapacitors, there has been extensive interest in developing commercial attractive transition-metal oxide (TMO) electrodes, as these TMOs are natural abundance, low cost, and environmental friendliness, and particularly can provide various oxidation states for efficient redox charge transfer and enable a higher energy density and a high theoretical specific capacitance. As with different microstructures and compositions, they show substantial differences in supercapacitor performance due to dissimilarities in the electrode/electrolyte interface properties and ion transfer rates during the charge storage processes. Therefore, in this doctoral dissertation, beginning with manganese dioxide, and then developing some Mn-based metal oxide composites to meet some challenges in the transition metal oxide electrode materials. A variety of one-dimensional, two-dimensional and three-dimensional Mn-based TMOs or multi-component composite TMO materials have been synthesized by hydrothermal method and electrochemical deposition, and then were characterized by means of XRD, SEM and TEM, and finally fabricated into electrodes to examine the electrochemical performances, in particular, improving their practical electrode applications. The main points of this dissertation are summarized as follows:1. Single-crystal α-MnO2ultralong nanowires (-40μm in length and～15nm in diameter) were synthesized by a simple process of hydrothermal treatment. By varying the surfactants, the other two kinds of a-MnO2nanostructures (nanorods and nanoflowers) were also prepared. The electrical conductivity of as-prepared MnO2nanowires and nanorods was then studied by a new STM-TEM holder, and their obtained results showed that the MnO2ultralong nanowires possess better electrical conductivity compared with MnO2nanorods, and both of the voltages were ranged from-5to5V, and the current value of MnO2ultralong nanowires varies from-252.5to206.7nA, while the MnO2NR varies from-122.3to92.3nA. Compared with as-synthesized a-MnO2nanorods and nanoflowers, individual α-MnO2ultralong nanowires showed a better electrochemical performance, and their based electrodes exhibited an enhanced specific capacitance of345F g-1at1A/g with high rate capability (54.7%at10A g-1).2. Ultrafine a-MnO2nanobelts (8-10nm in diameter) were synthesized by a facile, template-free and effective electrochemical method on Ni foam, and an extensive study of the electrode properties with respect to changes of the temperature has been carried out. Through both CV and galvanostatic CD investigation, the specific capacitance has been seen to increase with increasing temperature, with values as high as509F g-1observed at50℃, higher than that of in0and25℃. Also, this electrode demonstrated a good rate capability with39.1%retention even the scan rate increasing to100times (1to100mV s-1). More importantly, the specific capacitance of the MnO2nanobelt electrode has91.3%retention after5000cycles with repeated heating and cooling during temperature of0to50℃, showing good high temperature-resistive long-term cycle stability.3.3D hierarchical heterostructures of MnO2nanosheets or nanorods grown on Au-coated Co3O4porous nanowall arrays were designed and synthesized, looking like a sandwiched configuration of Co3O4@Au@MnO2, by a facial and controllable electrochemical deposition process. Due to their unique self-assembling architecture characteristics involving porous Co3O4nanowalls, ultrathin MnO2nanosheets, and a high conductivity Au layer sandwiched between them, each component provides much needed critical function for efficient use of metal oxide for energy storage. The synthesized3D hierarchical heterostructures exhibited favorable electrochemical performances such as a high specific capacitance as851.4F g-1at10mV s-1and1532.4F g-1at1A g-1, good rate performance and an excellent long-term cycle stability (nearly no degradation after5000cycles), thus could be considered as perspective materials for high-performance electrochemical capacitors.4. An urchin-like cubic phase MnCo2O5hierarchical structure with4～6μm in diameter was synthesized by a facile hydrothermal method followed by calculation in400℃. SEM and TEM characterizations confirmed that the unique hierarchical structure was composed of1D nanochains consisting of nanoparticles, making the MnCo204.5becomes a highly porous texture. As an electrode material, it exhibited a specific capacitance of151.2F g-1at scan rate of5mV s-1. More importantly, this unique electrode demonstrated an outstanding rate capability with83.6%retention even at the current density increasing to50times (0.1to5A g-1), and showed excellent long-term cycle stability that it nearly had no decrease after2100cycles at progressively varied current densities.更多还原