The proposed research will develop electrochemical storage materials based on three dimensional carbon nanotube composites. The carbon nanotube templated microfabrication (CNT-M) composites consist of patterned vertically aligned carbon nanotube (VACNT) templates coated with electrochemically active material. These structures allow for complex hierarchical structuring of the material on both the micro and nanoscale. An application where hierarchical structuring could play a transformational role is in high capacity battery materials, like nanostructured silicon, the target of the proposed work. Research on nanostructured silicon anodes has resulted in materials with extremely high specific capacities, but it has not generally resulted in materials with correspondingly high areal and volumetric capacity, which are also required for high capacity cells. Additionally, capacity stability is a challenge on these very high surface areas materials due to the formation of surface electrolyte interphase (SEI) layers. We will fabricate and test silicon CNT-M anodes that will provide a high degree of structural control, which we will use as a tool to study the influence of surface area on SEI stability and impact, and the influence of pore size, layer thicknesses and structure on electrode capacity at different rates. We will also extend this fabrication process to create microscale encapsulation cells for the nanostructured silicon material, separating the liquid electrolyte from the nanostructured silicon surface in order to control SEI stability and dramatically reduce the negative impact of SEI formation. In short, the proposed transformational work will allow us to understand and optimize the influence of electrode structure on the performance of energy storage electrodes in a way that has not previously been possible.
It also holds the promise of creating structurally engineered electrodes, including microencapsulated and three dimensional electrodes, for a new generation of high-performance electrical storage devices.
Objectives of the proposed work include:
1. Fabrication of hierarchically patterned silicon electrodes. Structures based on patterned VACNT templates that can facilitate optimal ion and electron conductivity, allow for control of the silicon/electrolyte interface using microencapsulation, and provide a platform for the development of three dimensional batteries will be fabricated.
2. Characterization and optimization of CNT-M electrodes. Structural and electrochemical characterization will be coupled with computational modeling to identify and quantify rate limiting mechanisms and the influence of geometry on rate and stability.
An interdisciplinary team of experts from BYU with an established record of successful collaboration has been assembled to take advantage of this transformational opportunity. The team includes a physicist with expertise in nanofabrication including extensive work in vertical nanotube growth and chemical vapor deposition; another physicist with expertise in nanoscale materials characterization including transmission electron, scanning transmission electron, and focused ion beam microscopy and microanalysis; and a chemical engineer with expertise in electrochemistry and energy storage materials and systems.
The intellectual merit of the proposed work is that it introduces potentially transformational electrochemical materials based on templated carbon nanotube composites. These new materials have the potential to enable the development of energy storage systems with both high energy density and high power density, including 3D electrodes. Energy storage with these characteristics is desperately needed to address a wide variety of issues in our rapidly changing energy generation and delivery systems. These unique materials also provide a well-controlled test bed for fundamental understanding of the structural factors that limit electrode performance.
Broader Impacts:
The broader impacts include the development of new energy storage materials with the potential to have significant societal and environmental impact. In addition, the proposed work will involve education of undergraduate and graduate students in a multidisciplinary environment where the specific training is in energy storage materials. The PI?s have a long track record of involving undergraduates in a positive research mentoring environment and will continue this effort. The impact of the work will be extended further through a primary school outreach program that will develop and sustain interest in science and technology by underrepresented groups.
