SUMMARY

Chemo-mechanics studies the material behavior and phenomena at the interface of mechanics and chemistry. Material failures due to coupled chemo-mechanical effects are serious roadblocks in the development of renewable energy technologies. Among the sources of renewable energies for the mass market, hydrogen and lithium-ion battery are promising candidates due to their high efficiency and easiness of conversion into other types of energy. However, hydrogen will degrade material mechanical properties and lithium insertion can cause electrode failures in battery owing to their high nobilities and strong chemo-mechanical coupling effects. These problems seriously prevent the large-scale applications of these renewable energy sources. In this thesis, An atomistic study of the chemical-mechanical failures at the nanoscale is performed for understanding the hydrogen embrittlement of grain boundary engineered metals and the lithium insertion induced fracture in alloy electrodes for lithium-ion batteries. Hydrogen in metallic containment systems such as high-pressure vessels causes the degradation of their mechanical properties that can result in sudden catastrophic fracture. A wide range of hydrogen embrittlement phenomena was attributed to the loss of cohesion of interfaces due to interstitially dissolved hydrogen. Our modeling and simulation of hydrogen embrittlement will address the question of why susceptibility to hydrogen embrittlement in metallic materials can be markedly reduced by grain boundary engineering. Silicon is one of the most promising anode materials for Li-ion batteries because of the highest known theoretical charge capacity. But Si anodes often suffer from pulverization and capacity fading. This is caused by the large volume changes of Si. In particular, large incompatible deformation between areas of different Li contents tends to initiate fracture, leading to electro-chemical-mechanical failures of Si electrodes. In order to understand the chemo-mechanical mechanisms, we begin with the study of basic fracture modes in pure silicon, and then study the diffusion induced deformation and fracture in lithiated Si. This thesis will provide an atomistic modeling framework for the study of chemo-mechanics of advanced materials such as nano-structured metals and alloys.