Atomic Scale Simulations of the Solid Electrolyte Li7La3Zr2O12 by Seungho Yu A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy (Mechanical Engineering) in the University of Michigan 2018 Doctoral Committee: Associate Professor Donald Siegel, Chair Professor Udo Becker Assistant Professor Neil Dasgupta Associate Professor Jeff Sakamoto Seungho Yu [email protected] ORCID iD: 0000-0003-3912-6463 © Seungho Yu 2018 Acknowledgements First, I would like to express my sincere appreciation to my advisor, Professor Don Siegel, for his invaluable mentorship during my Ph.D. studies. Without his guidance and persistent help this dissertation would not have been possible. I am also deeply grateful to Professor Jeff Sakamoto, whose research insights have been greatly beneficial and helpful to me. I additionally thank Professors Neil Dasgupta and Udo Becker for their valuable advice and service on my committee. I would like to thank Dr. Jeff Wolfenstine, Dr. Travis Thompson, Dr. Asma Sharafi, and Eric Kazyak for their experimental efforts. I am also grateful to members of the Siegel research group for their supportive discussions. This work was supported by the U.S. Department of Energy (DOE) Advanced Battery Material Research (BMR) program under Grant DE-EE-0006821 and Advanced Research Projects Agency – Energy (ARPA-e), grant no. DE-AR0000653. I also acknowledge financial support from the Kwanjeong Educational Foundation. Last but not least, I am greatly indebted to my parents and my wife, Sooyeon Kim, for their warm love, encouragement, and endless support. ii Table of Contents Acknowledgements .................................................................................................................... ii List of Tables............................................................................................................................ vii List of Figures ........................................................................................................................... ix Abstract ................................................................................................................................... xiv Chapter 1 Introduction ................................................................................................................ 1 1.1 Motivation ......................................................................................................................... 1 1.2 Solid Electrolytes .............................................................................................................. 2 1.3 Li7La3Zr2O12 (LLZO) ........................................................................................................ 4 1.4 Challenges ......................................................................................................................... 6 1.5 Goals and Outline .............................................................................................................. 8 Chapter 2 Methodology ............................................................................................................ 12 2.1 First Principles Calculations ............................................................................................ 12 2.1.1 Kohn-Sham Density Functional Theory .................................................................... 12 2.1.2 Exchange-Correlation Functional ............................................................................ 14 2.1.3 GW Methods ............................................................................................................ 16 2.1.4 Implementation ......................................................................................................... 17 iii 2.2 Classical Molecular Dynamics ....................................................................................... 18 2.2.1 Principles of Molecular Dynamics ............................................................................ 18 2.2.2 Force-Fields .............................................................................................................. 19 Chapter 3 Electronic Properties and Electrochemical Stability .................................................. 21 3.1 Introduction ..................................................................................................................... 21 3.2 Methodology ................................................................................................................... 22 3.2.1 Bandstructure and Density of States .......................................................................... 22 3.2.2 Band Edge Positions ................................................................................................. 23 3.3 Results and Discussion .................................................................................................... 27 3.3.1 Electronic Properties ................................................................................................. 27 3.3.2 Electrochemical Window .......................................................................................... 29 3.4 Conclusions ..................................................................................................................... 33 Chapter 4 Impact of Surface Contamination.............................................................................. 35 4.1 Introduction ..................................................................................................................... 35 4.2 Methodology ................................................................................................................... 36 4.2.1 Thermodynamic Driving Force of the Reaction ......................................................... 36 4.2.2 Work of Adhesion and Wetting Angle ...................................................................... 38 4.2.3 Li+ and H+ Ion Transport........................................................................................... 40 4.3 Results and Discussion .................................................................................................... 41 4.3.1 Impact of Air Exposure on Surface Chemistry .......................................................... 41 iv 4.3.2 Li Wettability at the Li-LLZO Interface .................................................................... 45 4.3.3 Impacts of Proton Contamination on the Transport Properties ................................... 47 4.4 Conclusions ..................................................................................................................... 51 Chapter 5 Elastic Properties ...................................................................................................... 52 5.1 Introduction ..................................................................................................................... 52 5.2 Methodology ................................................................................................................... 53 5.3 Results and Discussion .................................................................................................... 57 5.3.1 Elastic Properties of Al and Ta-Doped LLZO ........................................................... 57 5.3.2 Ductility and Elastic Anisotropy ............................................................................... 61 5.3.3 Elastic Properties of Metallic Lithium ....................................................................... 62 5.3.4 Discussion and Implications...................................................................................... 64 5.4 Conclusions ..................................................................................................................... 66 Chapter 6 Grain Boundary Contributions to Li-Ion Transport ................................................... 67 6.1 Introduction ..................................................................................................................... 67 6.2 Methodology ................................................................................................................... 69 6.3 Results and Discussion .................................................................................................... 72 6.3.1 The Energetics and Composition ............................................................................... 72 6.3.2 Li-ion Trajectory....................................................................................................... 75 6.3.3 Li-ion Diffusivity ...................................................................................................... 78 6.4 Conclusions ..................................................................................................................... 83 v Chapter 7 Grain Boundary Softening, A Mechanism for Lithium Metal Penetration ................. 85 7.1 Introduction ..................................................................................................................... 85 7.2. Methodology .................................................................................................................. 89 7.2.1 Molecular Dynamics ................................................................................................. 89 7.2.2 Elastic Properties ...................................................................................................... 94 7.3 Results ...........................................................................................................................