【作者】 赵生娜；

【导师】 宋怀河；

【作者基本信息】 北京化工大学 ， 材料科学与工程， 2010， 硕士

【摘要】 超级电容器是继锂离子电池之后的又一新型储能元件,近几年来逐渐成为新能源研究的热点。多孔碳材料由于具有较高的比表面积和稳定的化学性质而被广泛地用作超级电容器电极材料,但是由于其导电性较差、孔结构复杂等原因限制了其在超级电容器中的广泛应用。石墨烯作为一种单层的二维碳原子层,由于结构简单、导电性好、比表面积大而成为超级电容器电极材料的最佳选择之一本文以天然鳞片石墨和人造石墨为原料,通过氧化-热膨胀的方法制备出膨胀石墨,并在此基础上采用球磨法获得石墨烯纳米片,研究了石墨烯纳米片作为超级电容器电极材料的性能。对样品的形貌结构进行扫描电子显微镜、透射电子显微镜、X射线衍射、氮吸附比表面积测试、傅立叶红外光谱和拉曼光谱测试。在质量浓度为30%的KOH水溶液中进行了电化学充放电测试、循环伏安和交流阻抗测试。研究表明,以不同原料制备的膨胀石墨都具有蠕虫状多孔结构,膨胀人造石墨的体积膨胀倍率远小于膨胀天然石墨,但其比表面积却高于后者,分别为524m2·g-1和358m2·g-1。在相同充放电条件下,膨胀人造石墨电极的比电容量比膨胀天然石墨电极高,在100mA·g-1的电流密度下分别达到196F·g-1和157F·g-1,但随着电流密度逐渐增大到2000mA·g-1,前者的容量保持率低于后者。球磨后膨胀石墨的蠕虫状结构遭到破坏,形成片层状结构,随着球磨时间延长,碳原子堆垛层数先减少后增加,球磨3h样品堆垛层数最少,电镜照片显示其结构为相互堆叠的石墨烯纳米片。球磨后,且随着球磨时间延长,样品的比电容量先增加后减少,球磨3h时比电容量达到最大值,在100mA·g-1的电流密度为211F·g-1,4h和6h样品比容量有所降低,分别为170F·g-1和167F·g-1,但仍明显高于膨胀石墨电极。具体的原因可以从石墨烯纳米片的简单结构易于电解液的扩散、球磨过程中产生的表面缺陷有利于电荷的聚集等方面分析。随着电流密度不断增大,石墨烯纳米片电极都表现出了良好的容量保持率。更多还原

【Abstract】 Supercapacitor is a new-generation energy storage device after lithium ion battery and attracts worldwide researchers’interests as a promising high-power energy source in many fields. Many porous carbon materials have been investigated for supercapacitor electrode materials for their high specific surface areas and chemical stability. However, their specific surface capacities are always much lower than the theoretical value, which should be attributed to the anfractuous pore-texture and poor electric conductibility. Graphene as a two-dimensional layer with one atomic thickness has been proposed a competitive material for supercapacitors applications for its high specific surface area, electric conductivity and simple layer structure.In this thesis, graphene nanosheets (GNSs) were synthesized by grinding the expanded graphite which was prepared from natural flake graphite and artificial graphite via the oxidation-thermal explosion method and were applied as the electrode materials for supercapacitor. The morphologies and structures of both expanded graphite and GNSs were characterized by Scanning Electron Microscope, Transmission Electron Microscope, X-ray Diffraction, nitrogen adsorption measurement, Fourier transform InfraRed spectrum and Raman spectrum mea. Electrochemical performances as electrode materials for supercapacitor were studied by constant current Galvanostatic charge/discharge test, cyclic voltammetry and alternating current impedance in 30wt.% KOH electrolyte.The results show that expanded graphites prepared from different raw materials all have a worm-like porous structure. Expanded artificial graphite has not only a larger specific surface area of 524m-g-1 than that of expanded natural flakes graphite,358m2·g-1 exactly, but also a higher expansion volume. Under the current density of 100mA·g-1, the specific capacity of expanded artificial graphite is obviously higher than expanded natural flake graphite,196F·g-1 and 157F·g-1 respectively. However, its capacity retention is lower than the latter as the current density increasing to 1000mA·g-1 gradually. After milling, the worm-like porous structures are broken into randomly-oriented graphene nanosheets with a size distribution from tens to hundreds nanometers. The stacking height of GNSs samples present a decreasing-increasing trend and reach a weakest point at 3h milling. Accordingly, the specific capacities of GNSs increase obviously after milling as the milling time increases from 2h to 6h, and GNS-3h electrode achieves a highest specific capacity of 211F·g-1 at a current density of 100mA·g-1. For GNS-4h and GNS-6h, although specific capacity values obviously fall back, 170F·g-1 and 167F·g-1 respectively, there is a significant improvement compared to that of expanded natural flakes graphite. The reasons should be attributed to the simple layer structures of GNSs samples, lattice defects on the GNSs surfaces produced during the ball-milling process and so on. At the same time, although the specific capacity slightly decreases with the increasing of the current load from 100 to 2000mA·g-1 for each sample, all the GNSs samples keep excellent capacity retentions.更多还原