【作者】 顾鑫；

【导师】 钱逸泰；

【作者基本信息】 山东大学 ， 无机化学， 2014， 博士

【摘要】 由于日益凸显的能源危机、环境问题,核能、太阳能等产生的电能需得到高效储存的要求,发展高效、廉价和环境友好的储能装置就成为科学界和工业界面对的重要的挑战和机遇。二次锂离子电池相较于传统的铅酸、镍氢电池,具有高能量密度、电压平稳、自放电率小、持久的循环性能以及绿色环保等优点,在我们日常所用的小型移动电子设备中发挥着重要的作用。目前,随着锂离子电池在电动汽车和智能电网等大功率用电器和储能领域的发展,人们对商业化的锂离子电池提出了更高的要求。而高性能锂离子电池的实现依赖于其中电极材料的结构设计和性能提升。过渡金属氧化物负极材料具有高于传统的碳/石墨基负极材料2-3倍的理论比容量,是实现高容量、高功率、长寿命的锂离子电池的潜在电极材料。但是,其较差的电子电导率及循环过程中的体积效应限制了其应用。研究发现,纳米技术在过渡金属氧化物材料中的应用可以有效的缓解以上缺点。因此,发展过渡金属氧化物纳米电极材料来解决上述问题,对提高锂离子电池的整体性能具有重要的实际意义。在本论文中,我们旨在利用简单的方法构筑高性能的锂离子电池纳米电极材料,为锂离子电池负极材料的发展提供有益的探索。本论文的主要内容如下：(1)采用水热反应,首次在β-MnO2纳米棒表面成功外延生长α-FeOOH纳米棒。并通过时间演化,研究了该结构的生长过程。该β-MnO2/a-FeOOH枝状结构呈现出四次对称性的新颖特征,经高分辨透射电镜照片证明,主要是由于FeOOH的(010)晶面与Mn02的(100)晶面的晶格匹配。经过高温煅烧,得到结构保持的β-MnO2/a-Fe2O3枝状纳米棒。并且详细考察了β-MnO2纳米棒、α-Fe2O3多孔纳米棒以及β-MnO2/a-Fe2O3枝状纳米棒的电化学性能。β-Mn02/a-Fe2O3枝状结构具有最优异的电化学性能,在1Ag-1的电流密度下,循环200圈后,还能保持1028mAhg-1的比容量；在4Ag-1的电流密度下,比容量还能达到881mAhg-1。 β-MnO2/a-Fe2O3枝状结构具有的较高的比表面积、丰富的多孔性以及β-MnO2与α-Fe2O3之间的协同作用等对提高电极材料的性能起到至关重要的作用。(2)采用枝状β-MnO2/a-Fe2O3纳米棒与葡萄糖溶液在190℃下水热反应5小时,制备得到多级核壳α-Fe2O3@C纳米管。该纳米管继承了β-MnO2/a-Fe2O3结构的尺寸、形貌和多级的表面结构。通过调节反应物β-MnO2/a-Fe2O3纳米棒与葡萄糖的比例,得到具有不同碳层厚度的多级核壳a-Fe2O3@C纳米管,并研究了其锂离子电池负极性能。通过锂电测试发现,碳层最薄的样品具有最优的倍率性能和循环稳定性。他们在0.2和1Ag-1电流密度下循环100圈后,还能分别得到1173,1014mAh g-1的比容量。甚至在4Ag-1下循环1000圈,容量还能保持在482mAh g-1.该优异的电化学性能主要得益于多级核壳a-Fe2O3@C纳米管较薄的碳层,可以有效地促进电子、离子传输和抑制充放电过程中的体积效应。(3)采用MnOOH纳米棒为模版,利用吡咯单体的聚合反应,合成了MnOOH@PPy同轴纳米棒。MnOOH@PPy同轴纳米棒经过高温还原,得到了氮掺杂的碳包覆MnO同轴纳米棒结构(MnO@C-N)。研究了MnO@C-N与MnO的电化学性能,发现MnO@C-N具有明显增大的比容量、倍率性能和循环性能。Li/MnO@C-N电极在500mAg1电流密度下的循环100圈后,比容量达到982mAh g-1,相比于Li/MnO电极的703mAh g-1有了较大的提高。Li/MnO@C-N电极在1000mAg-1的大电流密度下循环900圈,还能保持679mAh g-1的比容量。该优异的电化学性能可以归结于氮掺杂的碳包覆一维结构,其可以有效地促进电荷转移和抑制体积效应。更多还原

【Abstract】 One of the most important challenges academia and industries are facing today is to provide high efficient, low cost and environmental friendly energy storage devices to address the problems of environmental pollution, the impending exhaustion of fossil fuels and to support the sustainable usage of green and clean energy sources likenuclear power,solar, etc. Since the practical applications of LIBs highly rely on the performance of electrodes, how to design and achieve high-efficient, low-cost and safe electrode materials turns into a great challenge. Transition metal oxides are promising electrode materials because of their high specific capacity, typically2-3times higher than that of carbon/graphite based materials. However, their cycling stability and rate performance still can not meet the requirements of practical applications due to their poor electronic conductivity and large volume expansion during cycling. It is reported that nanoscale materials can greatly increase the performance of the metal oxide electrodes. Therefore, numerous efforts are urgently required to design advanced electrode nanostructures with high performance in the application of electrochemical energy storage devices.In this paper, we rationally designed nanostructured electrode materials withexcellent electrochemical performance for the LIBs. The main results are as follows:(1) Hierarchical nanocomposites rationally designed in component and structure, are highly desirable for the development of lithium ion batteries, because they can take full advantages of different components and various structures to achieve the superior electro-chemical properties. Here, the branched nanocomposite with β-MnO2nanorods as the back-bone and porous α-Fe2O3nanorods as the branches are synthesized by a high-temperature annealing of FeOOH epitaxially grown on the β-MnO2nanorods. Since the β-MnO2nanorods grow along the four-fold axis, the as-produced branches of FeOOH and a-Fe2O3are aligned on their side in a nearly four-fold symmetry. This synthetic process for the branched nanorods built by β-Mn02/a-Fe2O3is characterized by XRD patterns, SEM, TEM and HRTEM images. The branched nanorods of β-MnO2/a-Fe2O3present an excellent lithium-storage performance. They exhibit a reversible specific capacity of1028mAh g-1at a current density of1000mA g-1up to200cycles, much higher than the building blocks alone. Even at4000mA g-1, the reversible capacity of the branched nanorods could be kept at881mAh g-1. The outstanding performances of the branched nanorods are attributed to the synergistic effect of different components and the hierarchical structure of the composite. The disclosure of the correlation between the electrochemical properties and the structure/component of the nanocomposites, would greatly benefit the rational design of the high-performance nanocomposites for lithium ion batteries in the future.(2) High-performance anode materials in lithium ion batteries greatly lie on the elaborate controls on their size, shape, structure and surface. However, it is difficult to assemble all the controls within one particle, due to difficulties in synthesis. Here, hierarchical carbon-coated a-Fe2O3nanotubes were prepared by a facile hydrothermal reaction between branched MnO2/Fe2O3nanorods and glucose. The resulting nanotubes realize all these controls in one particle in terms of nanoscale size, one-dimensional shape, hollow structure, hierarchical surface and carbon coating. Meanwhile, the thickness of the carbon layer could be easily controlled by the ratio between different reactants. Electrochemical measurements show that the core-shell nanotubes with a thinnest carbon layer give the best cycling and rate performances. They deliver a specific capacity of1173mAh g-1after100cycles at a current density of0.2A g-1,or1012mAh g-1after300cycles at1A g-1. Even after1000cycles at a current density of4A g-1, the specific capacity could be still kept at482mAh g-1. The excellent lithium-storage performances could be attributed to the well-designed controls in this nanocomposite and a thin carbon layer that increase the electron conductivity of the electrode and keep the carbon content lower simultaneously.(3) MnOOH@PPy coaxial nanorods were firstly prepared by the polymerization reaction of pyrrole in the present of MnOOH nanorods. Then, MnOOH@PPy core-shell nanorods tansformed to coaxial MnO@C-N nanorods after treated in Ar/H2at700℃o The Li/MnO@C-N electrode demonstrates a specific capacity of982mAh g"1after100cycles at500mA g-1, higher than that of Li/MnO electrode. Even after 900cycles at1000mA g-1,Li/MnO@C-N electrode can still display679mAh g-1. The excellent electrochemical properties are related to the rationally designed nanostructures, such as, one dimensional, carbon coating and N-doping.更多还原