SUBJECT: Ph.D. Dissertation Defense
BY: Xueju Wang
TIME: Friday, August 12, 2016, 10:00 a.m.
PLACE: MRDC Building, 4211
TITLE: Mechanics of Deformation and Failure in Rechargeable Battery Materials
COMMITTEE: Dr. Shuman Xia, Chair (ME)
Dr. Hailong Chen (ME)
Dr. David McDowell (ME)
Dr. Gleb Yushin (MSE)
Dr. Min Zhou (ME)
Dr. Ting Zhu (ME)


Rechargeable batteries are the current dominant energy storage solution for portable electronics, electric vehicles and stationary power management. In the development of next-generation rechargeable batteries, the mechanical degradation and failure in high-capacity electrode materials, such as silicon and germanium, have hindered their wider use. To obtain a thorough understanding of the deformation and fracture characteristics of these materials, an integrated experimental and computational investigation is conducted in this research. A nanomechanical study is conducted on the damage tolerance of electrochemically lilthiated silicon by both in-situ transmission electron microscopy (TEM) experiments and quantitative fracture toughness measurements. The mechanistic underpinnings of the experimental results are elucidated by molecular dynamics simulations. The fracture toughness of lithiated germanium is measured by nanoindentation and compared with that of lithiated silicon. A nanoscale deformation analysis method is also developed and applied for the quantitative measurement of diffusion- and reaction-induced deformation fields in lithiated amorphous silicon. Informed by the experimentally measured deformation and fracture characteristics, a computational cohesive zone model is developed and integrated with a chemo-mechanical two-way coupling continuum model. The integrated model is applied to investigate the effective fracture properties of ion-storage materials and fracture mechanisms of lithiated nanostructures. This highly integrative experimental and computational work has profound implications for the design and development of next-generation, high-performance rechargeable batteries. Furthermore, the experimental and computational methodologies developed in this work can be applied to study other micro- or nano-structured electrode/electrolyte architectures in various electrochemical systems.