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.
