Publication Date
2011
Document Type
Dissertation
Committee Members
Ronald Coutu, Jr. (Committee Member), Tarun Goswami (Advisor), Hong Huang (Committee Member), Bor Jang (Committee Member), Sharmila Mukhopahyay (Committee Member)
Degree Name
Doctor of Philosophy (PhD)
Abstract
Lithium-ion battery anodes with a nanostructure of randomly dispersed carbon nanofibers (CNFs), carbon nanotubes (CNTs), and nanoparticles of tin-oxide or silicon were fabricated and tested in order to develop high capacity, easily manufactured anodes. In these anodes, a mesh of CNTs and CNFs form a conductive network within which the nanoparticles of tin-oxide are suspended. The CNT network directs electron flow to and from the nanoparticles while accommodating their volume changes. The CNFs were intended to aid electron transport by serving as conduction channels between the CNTs and the current collector. Secondarily, the CNFs reinforce the physical structure of the anodes. The nanostructure of the anodes allows the electrolyte to freely penetrate, facilitating ionic transport. In most cases, the components of the anode were held together by Van der Waals forces. Both single-walled carbon nanotubes and multi-walled carbon nanotubes were used in this study in order to determine if there performance would be similar. The anodes take advantage of the specific capacity of tin and tin-oxide, which are 981 mAh/g and 1,491 mAh/g, respectively. Because tin is known to expand to three times its original size when it alloys with lithium, it is used in nanoparticle form for these anodes and thus avoids the tendency of tin to disintegrate. To achieve the desired nanostructure, processing methods based on buckypaper formation were explored. Sonication processes were experimented with to determine the optimum conditions for the fabrication of the anodes. Additionally, additives to aid in the binding of the tin-oxide nanoparticles to the CNTs were explored. These included the addition of polyvinylidene fluoride (PVDF) or carbonized phenolic resins. Anodes were found to exhibit the highest reversible capacity when the processing times were kept to a minimum. This was most likely due to the tendency of CNTs to shorten when sonicated. The shorter sonication times were sufficient to allow the desired level of entrapment of the tin-oxide nanoparticles by the CNTs without degrading the physical characteristics of the CNTs. While the CNTs were intended to move with the tin-oxide nanoparticles and maintain electrical contact as they expanded and contracted, it was discovered that a film of electrolyte-based material formed on the nanoparticles, CNTs, and CNFs, disrupting the current flow. A mechanistic model was developed to illustrate the internal degradation of the anodes. Resistance and reversible capacity prediction models were also developed. The resistance prediction model was used to confirm the effect of the CNFs on the electrical characteristics of the anodes. As its name implies, the reversible capacity prediction model can be used in future endeavors to predict the reversible capacity that may be obtained in buckypaper anodes with various percentages of constituents and processing times.
Page Count
158
Department or Program
Ph.D. in Engineering
Year Degree Awarded
2011
Copyright
Copyright 2011, all rights reserved. This open access ETD is published by Wright State University and OhioLINK.
