Electrochemically-induced Phase Transition in Olivine Type Cathode Materials By Kai Xiang Bachelor of Engineering. Materials Science and Engineering Tsinghua University, 2011 Bachelor of Arts, Economics Tsinghua University, 2011 Submitted to the Department of Materials Science and Engineering in Partial Fulfillment of the Requirement for the Degree of Doctor of Philosophy in Materials Science and Engineering at the Massachusetts Institute of Technology February 2018 © 2018 Massachusetts Institute of Technology All rights reserved Signature of Author: Department of Materials Science and Engineering January 3rd, 2018 Certified by: Yet-Ming Chiang Kyocera Professor of Ceramics Thesis Supervisor Accepted by: Donald Sadoway John F. Elliott Professor of Materials Chemistry Chair of the Graduate Committee 1 2 Experimental and Numerical Study of Electrochemically-induced Phase Transition in Olivine Type Cathode Materials By Kai Xiang Submitted to the Department of Materials Science and Engineering on January 3rd, 2018 in Partial Fulfillment of the Requirement for the Degree of Doctor of Philosophy in Materials Science and Engineering Abstract Phase transitions are commonly observed in ion storage compounds when being used in rechargeable batteries and thus, the phase behavior of ion storage compounds as electrode active materials has significant impact on battery performance. This thesis aims to understand the interplay between materials structure, phase behavior and battery performance. The effects of operating conditions, especially overpotential and temperature, on phase behavior and battery performance are also investigated. Using olivine-type phosphates (i.e. phospho-olivines) with varying composition and particle size as model system, strain accommodation mechanism within single nanoparticles (Chapter 2 to 3) and mesoscale kinetics of nanoparticle aggregates (Chapter 4 to 5) during electrochemically-induced phase transition have been systematically investigated. In the first part, phospho-olivines with varying transformation strain, from 0 – 3vol% for LiMnyFe1-yPO4 (LMFP, y<0.5), 5vol% for LiFePO4 (LFP), to 17vol% for NaFePO4 (NFP), have been studied using operando Powder X-ray Diffraction (PXD), among other methods. While small transformation strain as in LMFP is accommodated and even avoided by formation of metastable solid solution, large transformation strain as in NFP is mitigated by formation and dissolution of intermediate amorphous phase. This novel mechanism to accommodate large transformation strain may pave the way of utilizing battery materials that deem not working otherwise. In the second part, potentiostatic studies are conducted and a model modified from Avrami model is developed to quantitatively describe phase transformation progresses. The phase transition of LMFP and LFP nanoparticle aggregates is found to follow a nucleation and growth process while the growth is governed by lithium ion diffusion. Based on analysis using the modified Avrami model, more instantaneous nucleation and facile growth tend to occur when transformation strain is small (intermediate Mn content and/or small particle size), overpotential is high and/or temperature is high. And instantaneous nucleation and facile growth improve the 3 rate capability of batteries. The relationship between phase behavior and material structure as well as operating conditions is attributed to: 1) decreasing transformation strain reduces energy barrier for both nucleation and growth; 2) increasing overpotential and temperature boost the electrochemical driving force for phase transition and promote more instantaneous nucleation and facile growth. Thesis Supervisor: Yet-Ming Chiang Title: Kyocera Professor of Ceramics 4 Acknowledgements To begin with, I would like to thank my family for supporting my pursuit of PhD study. One of my parents’ dreams is to see their son graduating from the most prestigious engineering school on this planet. Unfortunately, my father would never be able to see this moment to come. Besides my family, I would like to first and foremost express my deep gratitude to my thesis supervisor, Professor Yet-Ming Chiang, for supporting my study at MIT continuously. It has been a great opportunity to work with him and learn from him. Not only have I honed my critical thinking and research skills under his guidance, but also I have developed professionally in other aspects, such as effective presentation skills and hypothesis-driven problem solving skills. I would also like to give the same gratitude to Professor Ming Tang, who has been my mentor on modeling part of my thesis and has put a lot of time discussing with me. I would also like to thank Professor Ju Li and Professor Silvija Gradecak for serving on my thesis committee and for their insights and comments on my thesis. I would also acknowledge funding support from DEO BES Physical Behavior of Materials Program under grant # DE-SC0002626. I would like to give special thanks to Professor Dorthe Ravnsbaek and Professor Zheng Li. Dorthe led me into operando synchrotron powder X-ray diffraction (SR-PXD) studies when she worked in our group as a Carlsberg Postdoc Fellow and continues working as a collaborator after she leaves MIT for professorship back in Denmark. Zheng taught me a great deal about battery materials and guided me to work on developing multiple electrode materials, which led to several high impact publications. Together with Zheng and Kevin Berkemeyer, I developed some big picture on energy storage when exploring the feasibility of commercializing a high power aqueous sodium ion battery technology developed in our group. We formed the team Sodium Energy and won a few business plan contests. I learned a lot through the process. I would also like to thank my collaborators and I really appreciate their help over the course of my PhD study. They are Dr. Karena Chapman, Dr. Peter Chupas, Dr. Olaf Borkiewicz and Dr. Kamila Wiaderek at Advanced Photon Source (APS), Argonne National Laboratory; Dr. Jianming Bai, Dr. Lijun Wu, Dr. Yimei Zhu at Brookhaven National Laboratory; Dr. Ke An at Oak Ridge National Laboratory; Dr. Chongmin Wang and Dr. Meng Gu at Pacific Northwest National Laboratory. I would like to give special thanks to Dr. Ananya Renuka Balakrishna and Dr. Frank Fan, who helped review my thesis and offered great suggestions for revision. Also thanks to awesome group members in Professor Yet-Ming Chiang Group. Besides names already mentioned, group members with whom I have frequent interactions are Linsen Li, Wenting Xing, Li Sun, William “Billy” Woodford, Allen “Red” Ransil, Rachel Zucker, Giovanna Bucci, Ruhul Amin, Bohua Wen, Sam Pan, Liang Su, Ping-Chun Tsai, Ariel Jackson, David Young, Tushar Swamy, Richard Park and Yiliang Li. Besides, I would like to give thanks to Toni Centorino, Maria Tsafoulias, who have been helping with order processing and travel reimbursements. I would like to give the same gratitude to Angelita Mireles and Elissa Haverty who provided prompt help and advice throughout my graduate school. 5 Outside of research, I have been taking a few initiatives at/around MIT, where I met a lot of awesome people. Many thanks to Stephen Rodan, Jessica Bryant, Thomas Petersen, Zhao Zhu, Akwasi Owusu-Akyaw and many more, with whom I founded MIT Energy Hackathon, which has evolved to become an annual event with hundreds of participants from all over the world. Many thanks to Coach Wei, Yue Guan, Xinkai Fu, Haozhe Wang, Tianyi Chen, Shuguang Li, Mandy Zhu, among others, with who I founded MIT Chinese Entrepreneurs Organization (MIT CEO), which has become a high level platform for business leaders, investors, entrepreneurs and researchers to communicate and collaborate. Another organization which I have been spending quite a bit time on is Tsinghua Alumni Association at Greater Boston (THAA-Boston). I have had great time and learn a lot from all volunteers there, especially Wei Lin, Zhenke (Jack) Liu, Song Han, Xiaodan Zhuang, Yang Song, Jia Xue, Jing Zhang, Ji Zhao, and many others. Together with Aly Eltayeb, Pavitra Krishnaswamy and Tunde Alawode, we won the 1st Prize at 2013 Harvard-MIT Case Competition. It was a great experience and I got exposed to consulting industry as a result. I would love to thank my consulting buddies, William Herbert, Ming Jiang, Summer Zhao and Bangqi Yin, who helped me get an intern offer from Boston Consulting Group. I have also had some badass roommates at MIT, many of whom have become entrepreneurs, including Dr. Feng Tan, Dr. Zhifei Ge, Dr. Lixin Shi and Maxim Lobovsky. Another roommate, Rohan Paul, was nominated as TR35 by prestigious MIT Technology Review. I have been benefiting a lot from living and communicating with them. I have harvested tremendous energy from my running buddies at Tsinghua Running Club at Boston and BEN Running Club. Ming Lei, Chunhua Liu, Wei Lin, Man Peng, Bing Wang and Thomas Petersen have inspired me to become a serious runner and have shared a lot of wisdom with me both in running and in life. I have also been enjoying Poker at MIT, where Poker is studied and practiced with the highest scientific rigor. I learned from a lot of poker pros at/around MIT including Maokai Lin, Kai Pan, Di Chen, Xianwen Mao, Kelvin Wu, Hang Chen, Feng Tan, Cheryl Cui, Helen Li, Kelvin Teo and many more. Last but not least, I would give special thanks to my skiing buddies, with whom I am able to free myself from setbacks in work and life, including Aurora Shen, Terry Xie, Daniel Wu, Daniel Xia, Yong Sun, Guangda Shi