Degree Type

Dissertation

Date of Award

2014

Degree Name

Doctor of Philosophy

Department

Aerospace Engineering

First Advisor

Valery I. Levitas

Abstract

Hollow nanoparticles (NPs) are produced by void nucleation and growth during chemical reactions. However, there is no proper understanding of nucleation and growth mechanisms, and their predictive modeling. Furthermore, models based on the Kirkendall effect predict the process time, which is larger by orders of magnitude than in the experiment. A continuum-mechanics approach for nucleation and growth of a nanovoid in reacting NPs based on the Kirkendall effect is developed, which quantitatively describes the experimental results for oxidation of copper NPs. The results show that the core is under compression (which eliminates fracture hypothesis) which promotes void nucleation by decreasing equilibrium concentration of vacancies at the void surface.

Si is a promising anode material for Li-ion batteries, since it absorbs large amounts of Li. However, insertion of Li leads to 334 % of volumetric expansion, huge stresses, and fracture; it can be suppressed by utilizing nanoscale anode structures. Continuum approaches to stress relaxation in LixSi, based on plasticity theory, are unrealistic, because the yield strength of LixSi is much higher than the generated stresses. Here, we suggest that stress relaxation is due to anisotropic (tensorial) compositional straining that occurs during insertion-extraction at any deviatoric stresses. Developed theory describes known experimental and atomistic simulation data. The stress evolution is modeled for different nanostructures (thin film, solid, and hollow nanoparticle) during lithiation-delithiation.

DOI

https://doi.org/10.31274/etd-180810-3507

Copyright Owner

Hamed Attariani

Language

en

File Format

application/pdf

File Size

102 pages

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