Nanostructured Electrochemical Materials

非技术描述：在这个项目中，氧化锡涂层的碳纳米管被用作模型材料来研究锂的储存机制。氧化锡由于具有较高的锂离子存储容量，被认为是锂离子电池最有前途的金属氧化物负极材料之一。然而，氧化锡作为阳极材料的实际应用受到其在充放电循环中体积变化大（可达300%）的限制，这可能导致其分解和与集流器的电断开。为了解决这一问题，在垂直排列的碳纳米管上生长氧化锡壳，形成了三维碳纳米管-氧化锡核-壳纳米线阵列。碳纳米管作为氧化锡壳的骨架，缓冲了较大的体积变化，而圆柱形氧化锡壳则减轻了氧化锡壳在锂化过程中的降解。该项目的成果将有利于常规锂离子电池的研发，以及片上微电源的开发。对锂离子电池三维分层电极纳米材料电化学性能的深入了解，对其开发和合理设计具有重要意义。这些研究人员每年提供两次公开讲座，以传达材料科学与技术的新知识。佛罗里达国际大学（Florida International University）是一所为西班牙裔服务的机构，参与这项研究的学生各不相同。每年，研究生和本科生都参与这项研究，他们有机会在桑迪亚国家实验室工作。每年，60名高中生和10名高中教师被邀请进行校园实验室参观和研究演示。技术细节：碳纳米管-金属氧化物核壳复合材料是锂离子电池负极材料的理想选择。然而，这类材料的电化学锂化-衰减行为和机理尚不清楚。对纳米级锂化机理的全面了解有助于高性能锂离子电池材料的设计和开发。该项目开发了一种协同方法来合成和表征垂直排列的碳纳米管-氧化锡核-壳纳米线阵列，以在合成时操纵其电化学性能。采用等离子体增强化学气相沉积的方法在集流器上直接合成了垂直排列的碳纳米管阵列，并通过化学溶液和气相沉积的方法在碳纳米管上合成了氧化锡外壳。采用电子显微镜、电子能量损耗谱、能量耗散谱、x射线衍射（原位和非原位）、充放电测量、循环伏安法、电化学阻抗谱和原位透射电镜观察锂化过程，研究了碳纳米管-氧化锡核-壳纳米线的微观结构和电化学性能。该研究有助于更好地了解核壳纳米线阵列的锂化机理及其微观结构对电化学性能的影响。研究结果为研究碳纳米管-金属氧化物复合材料在锂离子电池中的电化学过程提供了新的思路。研究生和本科生接受高级电化学材料合成、表征和设计方面的研究培训。

NON-TECHNICAL DESCRIPTION: In this project, tin oxide-coated carbon nanotubes are being used as a model material to investigate the mechanism for lithium storage. Tin oxide is considered one of the most promising metal-oxide anode materials for lithium ion batteries due to its high lithium ion storage capacity. However, the practical application of tin oxide as anode material is restricted by its large volume change (up to 300%) during charge-discharge cycles, which can cause its disintegration and electrical disconnection from the current collector. To circumvent this problem, a three-dimensional carbon nanotube-tin oxide core-shell nanowire array is being developed by growing tin oxide shells on vertically-aligned carbon nanotubes. The carbon nanotubes serve as the backbone of the tin oxide shell to buffer the large volume change, while the cylindrical tin oxide shell alleviates its degradation during the lithiation process. This project's outcomes will be beneficial to conventional lithium ion battery research and development, as well as on-chip micropower development. A better understanding of the electrochemical properties is making a significant contribution to the development and rational design of three-dimensional hierarchical electrode nanomaterials for lithium ion batteries. Each year, these researchers provide two public lectures to convey new knowledge of material science and technology. A diverse set of students are engaged in the research at Florida International University, a Hispanic-Serving Institution. Each year, graduate and undergraduate students participate in the research, and they have the opportunity to work at Sandia National Laboratories. Annually, 60 high school students and 10 high school teachers are invited for on-campus lab tours and research demonstrations. TECHNICAL DETAILS: Carbon nanotube-metal oxide core-shell composite materials are promising candidates for application as anode materials in lithium ion batteries. However, the electrochemical lithiation-delithiation behavior and mechanism of this type of materials remain unclear. A comprehensive understanding of the lithiation mechanism at the nanoscale benefits the design and development of high-performance lithium ion battery materials. This project develops a synergistic approach for the synthesis and characterization of vertically aligned carbon nanotube-tin oxide core-shell nanowire arrays to manipulate their electrochemical property at the time of synthesis. The vertically-aligned carbon nanotube arrays are synthesized directly on a current collector using plasma enhanced chemical vapor deposition, and the tin oxide shell on the carbon nanotubes is synthesized via chemical-solution and vapor deposition routes. The microstructure and the electrochemical properties of the carbon nanotube-tin oxide core-shell nanowires are being investigated by a combination of electron microscopy, electron energy loss spectroscopy, energy dissipation spectroscopy, X-ray diffraction (both in situ and ex situ), charge-discharge measurement, cyclic voltammetry, electrochemical impedance spectroscopy, and in situ transmission electron microscopy observation of the lithiation process. The study provides a better understanding of the lithiation mechanism of the core-shell nanowire array and the influence of their microstructure on their electrochemical properties. The research results provide new insight into the electrochemical process of carbon nanotube-metal oxide composite materials in lithium ion batteries. Graduate and undergraduate students receive research training in advanced electrochemical material synthesis, characterization and design.