University of Tennessee, Knoxville TRACE: Tennessee Research and Creative Exchange Doctoral Dissertations Graduate School 12-2019 Understanding Cathode Electrolyte Interfaces of Nickel-Rich LiNixMnyCozO2 Electrodes Nathan Phillip University of Tennessee, [email protected] Follow this and additional works at: https://trace.tennessee.edu/utk_graddiss Recommended Citation Phillip, Nathan, "Understanding Cathode Electrolyte Interfaces of Nickel-Rich LiNixMnyCozO2 Electrodes. " PhD diss., University of Tennessee, 2019. https://trace.tennessee.edu/utk_graddiss/5697 This Dissertation is brought to you for free and open access by the Graduate School at TRACE: Tennessee Research and Creative Exchange. It has been accepted for inclusion in Doctoral Dissertations by an authorized administrator of TRACE: Tennessee Research and Creative Exchange. For more information, please contact [email protected]. To the Graduate Council: I am submitting herewith a dissertation written by Nathan Phillip entitled "Understanding Cathode Electrolyte Interfaces of Nickel-Rich LiNixMnyCozO2 Electrodes." I have examined the final electronic copy of this dissertation for form and content and recommend that it be accepted in partial fulfillment of the equirr ements for the degree of Doctor of Philosophy, with a major in Energy Science and Engineering. Claus Daniel, Major Professor We have read this dissertation and recommend its acceptance: Gabriel Veith, Thomas Zawodzinski Jr., Claudia Rawn Accepted for the Council: Dixie L. Thompson Vice Provost and Dean of the Graduate School (Original signatures are on file with official studentecor r ds.) Understanding Cathode Electrolyte Interfaces of Nickel-Rich LiNixMnyCozO2 Electrodes A Dissertation Presented for the Doctor of Philosophy Degree The University of Tennessee, Knoxville Nathan Dale Phillip December 2019 Copyright © Nathan Dale Phillip All rights reserved. ii Dedication To my mother, for teaching me patience; to my father, for teaching me work ethic; to my brother, for friendship when it was hard to come by; and to my fiancée, for always being there for me. iii Acknowledgements This work could not have been done without my immense support network. I thank my family, friends, mentors, and colleagues for helping me throughout my graduate work and everything that led to it. To all my group members in their innumerable projects at Oak Ridge National Laboratory, I say thank you for guiding me to become a scientist, collaborating with me on fascinating experiments, and teaching me how to use our countless instruments. I appreciate my group leader, Nancy Dudney, for welcoming me to the family she has set up and providing me with access to the people and resources I needed to excel. I am grateful for my office mates who provided a bottomless font of laughter to wash away the stress of the day, as well as for being gracious guinea pigs for my baking projects. I thank my dissertation committee: Gabriel Veith, Claus Daniel, Thomas Zawodzinski, and Claudia Rawn, for mentoring me through the tortuous process of earning a PhD. Above all I thank Gabe for without his magnanimous patience and encouragement in the face of what was called, “an aggressive timeline,” for finishing my research, this work simply would not have come to fruition. I am indebted to his wisdom and mentorship and look forward to repaying the favor in kind down the road. I also had many informal mentors: Andrew Westover, Beth Armstrong, Robert Sacci, Andrew Kercher, David Wood, Jianlin Li, Lee Riedinger, Tom Rogers, and Lynn Youngs all enriched my multi-faceted adventure through the Bredesen Center, and I appreciate their time and dedication to me beyond what their job titles required. And to my fellow students in the Bredesen Center and other programs, it was my pleasure to work along side you and share stories on our journeys. I am particularly grateful to Jonathon Romero, Ashley Cliff, David Reeves, and David Garcia, who have remained my close friends ever since I first bumped into them in our first years of graduate school. Despite our different interests and paths, I have loved having a group to step away from it all and enjoy board games and movies with. Katie Browning and Landon Tyler, thank you for welcoming me to the lab group with open arms. You were the cornerstone of our happy office space with all the wonderful interns and post- bachelor’s who joined us, and I am honored to call you friends. My friends in Ohio also deserve praise here: Josh Godar, Jack Brinton, Max Pauly, Kevin Nicholson, Katherine Thomas, Maggie Perme, and Alex Merk, I know it was bittersweet when I left for Tennessee, so thank you all for giving me a second home to come back to for weekends and vacations. And to my other Ohio friend who became my fiancée, climbing partner, backpacking partner, SCUBA buddy, gaming partner, and soon to be partner in life, Tori Delap, thank you. I love you for all the adventures we have had together and have planned together. You gave me an excuse to climb and backpack throughout the Southeast and explore more of Florida and Texas than I ever thought I would during my four years here. Thank you for making time for me despite your own hard-won journey through flight school and hanging out with us nerds instead of your cool pilot friends. Thank you for finding patience and sympathy even during journeys into uncut wilderness where you may have questioned my sanity and my definition of fun. I cannot wait to go on countless adventures with you in Washington and wherever else life may lead us. And finally, I thank my family. Mom and Dad, thank you for raising me to be the man I am today and for supporting me even as my passions have drawn me further from home. You have always been my biggest fans and it warms my heart to share my experiences with you. Ty, you have always been my best friend and I do not know how I would get through it all without having you to talk with on the phone or through a headset when gaming. Thank you for visiting me in iv Knoxville and going on road trips which I plan down to the half penny, and for keeping me grounded to Earth along the way. I could not have asked for a better older brother. To my cousins: few members of the broad Phillip family had ventured outside of the Chicagoland area before I went to Ohio and eventually Tennessee, and I know it was hard for us to be apart because most of us grew up within three blocks of each other. It has been one of my greatest pleasures in life to watch you all grow up despite Ty and me influencing you as troublesome older cousins. Ryan, Nick, Brad, Joe, Emily, Anna, Amira, and Sam, the more people I meet, the more I realize how fortunate we were to grow up as friends. A big part of that is due to my grandparents, so thank you Grandma Judy, Gramps, Grandma Pat, and Grandpa Jim for making sure we all played together nicely and had an awesome lake house to hang out at. I am grateful for this family and look forward to sharing these lessons as I expand my own branch of it. v Abstract The rapid growth of the energy storage market has fueled demand for battery materials with higher energy densities, longer cycle lives, and better safety features. This necessitates pushing the limits of known structures such as Ni-rich LiNixMnyCozO2 (x + y + z = 1) cathodes which offer high energy densities (>200 mAh/g) at high cutoff voltages (≥ 4.5 V vs. Li/Li+). Pushing into this high voltage regime introduces challenges of structural rearrangement, electrolyte decomposition, and the formation of an unstable cathode/electrolyte interphase layer (CEI) comprised of decomposition products. The CEI is poorly understood at high voltages but considered critical for passivating these materials against continuous degradation. This thesis addresses that knowledge gap through the development of thin film cathodes which were applied as a model system for studying interfacial modifications. Polymeric binders were deposited in various morphologies and found to reduce interfacial resistance by an order of magnitude compared to uncoated samples. The formation of a thin, LiF-rich passivation layer informs the selection of future binding agents as well as processing conditions for thin uniform coatings in commercial cells. Modification of the initial surface chemistry of the cathode by thin metal oxide coatings of varying isoelectric points demonstrated that an acidic surface is more effective for capacity retention and a stable CEI than more neutral or basic surfaces. This answered the question of how surface treatment of cathode materials influences electrolyte degradation at the surface and indicated that future efforts should focus on coatings which preferentially react with Li salts to form a fluorinated interphase. The degradation mechanism of NMC622 was deconvoluted from challenges of liquid electrolytes which are unstable at high voltages through the construction of the first Ni-rich NMC/Lipon/Li solid state battery. It was determined that using a solid electrolyte which is proven at high voltages did not stabilize the NMC material with cycling, indicating that despite interest of the field, Ni-rich NMC cathodes are not viable for solid state batteries without structural modification. This also demonstrated that accessing additional Li inventory with high voltage operation of Ni-rich NMC is not enabled by a stable CEI alone. vi Table of Contents 1. Why Study Ni-rich Lithium Ion Battery Interfaces? .............................................................. 1 1.1 The Lithium-ion Battery ............................................................................................