SUBJECT: Ph.D. Dissertation Defense
BY: Hao Luo
TIME: Monday, October 30, 2017, 10:00 a.m.
PLACE: MRDC Building, 2405
TITLE: Predictive Modeling of Degradation Mechanisms in Advanced Lithium Batteries and Barrier Coatings
COMMITTEE: Dr. Ting Zhu, Chair (ME)
Dr. Hailong Chen (ME)
Dr. Meilin Liu (MSE)
Dr. Mattew McDowell (ME)
Dr. Olivier Pierron (ME)
Dr. Shuman Xia (ME)


Lithium batteries play a critical role in the emerging landscape of renewable energies. Silicon is a promising candidate to replace the currently used graphite anode in Lithium batteries. However, the mechanical degradation of Si anode induced by the large volume changes during charge and discharge hinders its wide applications. To mitigate the degradation, Si nanowires, nanotubes or nanaparticles with surface coatings are often used. But it remains unclear regarding the effects of coatings and structural changes on the degradation mechanisms in Si anodes. In this work, a predictive chemomechanical model has been developed to account for two-phase lithiation/delithiation and large volume changes during the lithiation and delithiation process. Combined with in situ transmission electron microscopy experiments, this chemomechanical model has been used to investigate the degradation mechanisms in Si nanowires, nanotubes and nanoparticles with coatings. The optimal design of coatings has been explored to maximize the benefits of Si based anodes. In addition to lithium batteries, barrier coatings are crucial for the reliable operation of flexible electronics. To characterize the strain limits of barrier coatings in flexible electronics, a singular value of critical onset strain is often used. However, such metrics do not account for time-dependent or environmentally assisted cracking, which can be critical to the overall reliability of these thin-film coatings. To address issue, the time-dependent channel crack growth behavior of silicon nitride barrier coatings on PET (polyethylene terephthalate) substrates has been investigated in dry and humid environments. To elucidate the origin of the time-dependent crack growth behavior, predictive numerical simulations has been carried out based on the continuum elastic-viscoplastic model. The integrated experiment and modeling provide insight and guideline for the optimal design of reliable barrier coatings. Overall, the models and numerical procedures developed in this thesis will provide an effective platform for further study of the reliable lithium batteries and barrier coatings.