The Woodruff School

SUMMARY

Lithium-ion (Li-ion) batteries, which have revolutionized portable electronics, are key to the electrification of transportation vehicles. The development of next-generation Li-ion batteries requires high-capacity electrodes with a long cycle life. However, the high capacity of Li storage is usually accompanied by large volume changes, dramatic morphological evolution, and mechanical failures in the electrodes during charge and discharge cycling. To understand the degradation of electrodes and resulting loss of capacity, this thesis aims to develop mechanistic-based models for predicting the chemo-mechanical processes of lithiation and delithiation in high-capacity electrode materials. The modeling studies will be tightly coupled with in-situ transmission electron microscopy (TEM) experiments to gain unprecedented mechanistic insights into electrochemically-driven structural evolution and damage processes in high-capacity electrodes. To this end, we will develop both continuum and atomistic models that simulate mass transport, interface reaction, phase and microstructural evolution, stress generation and damage accumulation through crack or void formation in the electrodes. Our models have been successfully applied to the study of two-phase lithiation and associated stress generation in both crystalline and amorphous silicon electrodes. In the proposed research, we will further develop these models to study (i) composite nanowire electrodes, including SiOx-coated silicon nanowires under lithiation and bilayer carbon nanofibers under sodiation; (ii) crack patterning in lithiated silicon thin films; (iii) nanovoid formation in germanium nanoparticles during delithiation; and (iv) reactive force field (ReaxFF)-based atomistic simulations of lithiation in silicon. Our modeling research will be tightly coupled with in-situ and ex-situ experiments, so as to provide novel insights into how to mitigate electrode degradation and enhance capacity retention in Li-ion batteries. More broadly, our work has implications for the design and the development of nanostructured electrodes in high-capacity lithium-ion batteries.

SUBJECT:	Ph.D. Proposal Presentation

BY:	Feifei Fan

TIME:	Thursday, May 1, 2014, 10:00 a.m.

PLACE:	MRDC Building, 4211

TITLE:	Revealing Novel Degradation Mechanisms in High-Capacity Battery Materials by Integrating Predictive Modeling with In-Situ Experiments

COMMITTEE:	Dr. Ting Zhu, Chair (ME) Dr. Min Zhou (ME) Dr. Meilin Liu (MSE) Dr. Gleb Yushin (MSE) Dr. Shuman Xia (ME) Dr. Hailong Chen (ME)

SUMMARY Lithium-ion (Li-ion) batteries, which have revolutionized portable electronics, are key to the electrification of transportation vehicles. The development of next-generation Li-ion batteries requires high-capacity electrodes with a long cycle life. However, the high capacity of Li storage is usually accompanied by large volume changes, dramatic morphological evolution, and mechanical failures in the electrodes during charge and discharge cycling. To understand the degradation of electrodes and resulting loss of capacity, this thesis aims to develop mechanistic-based models for predicting the chemo-mechanical processes of lithiation and delithiation in high-capacity electrode materials. The modeling studies will be tightly coupled with in-situ transmission electron microscopy (TEM) experiments to gain unprecedented mechanistic insights into electrochemically-driven structural evolution and damage processes in high-capacity electrodes. To this end, we will develop both continuum and atomistic models that simulate mass transport, interface reaction, phase and microstructural evolution, stress generation and damage accumulation through crack or void formation in the electrodes. Our models have been successfully applied to the study of two-phase lithiation and associated stress generation in both crystalline and amorphous silicon electrodes. In the proposed research, we will further develop these models to study (i) composite nanowire electrodes, including SiOx-coated silicon nanowires under lithiation and bilayer carbon nanofibers under sodiation; (ii) crack patterning in lithiated silicon thin films; (iii) nanovoid formation in germanium nanoparticles during delithiation; and (iv) reactive force field (ReaxFF)-based atomistic simulations of lithiation in silicon. Our modeling research will be tightly coupled with in-situ and ex-situ experiments, so as to provide novel insights into how to mitigate electrode degradation and enhance capacity retention in Li-ion batteries. More broadly, our work has implications for the design and the development of nanostructured electrodes in high-capacity lithium-ion batteries.