Advanced Electrolyte System Design of Battery towards Expanded Applications on Energy Storage A Dissertation Submitted to the Faculty of the WORCESTER POLYTECHNIC INSTITUTE In partial fulfillment of the requirement for the Degree of Doctor of Philosophy in Materials Science and Engineering by Jiayu Cao November 2020 Approved by: Dr. Yan Wang, Advisor, Professor, Mechanical Engineering Dr. Brajendra Mishra, Head of the Materials Science and Engineering Program Abstract The battery technology is approaching a larger share portion of the energy storage demands nowadays. These sustainable electrochemical-based methods are gradually replacing the traditional fossil resource to power the world with its carry-on capability and eco-friendly nature. Many applications such as, military power supplies, civil transportation, and stationary storage need higher energy density of the rechargeable battery as the development of society. For example, the goal of commercializing next-generation electric vehicles which can satisfy a longer traveling distance is hard to achieve since the lack of lower cost, higher energy density and longer cycling life rechargeable batteries as next-generation energy storage devices. Both lithium sulfur (Li-S) battery and lithium ion battery (LIB) with silicon anode have potential to be the next-generation storage batteries. Because sulfur and silicon are both stored largely on earth, exploited easily and low cost. Therefore, a variety of deep dive and large-scale research have been started about Li-S battery and Si anode applied in LIB. Over the last few years, Argonne National Laboratory team has developed various ideas and methods to optimize Li-S battery and Si anode used in LIB, such as, introducing appropriate co- solvents and additives, replacing traditional electrolyte with ionic liquid and polymer electrolyte and enhancing Si anode by surface modification. For a comprehensive study, here we discuss four design schemes based on two major problems and one main barrier of Li-S battery and Si anode, respectively. In terms of Li-S battery, the first problem is the rapid capacity fading during cycling process and the second problem is the lithium polysulfide shuttling. The main barrier of Si anode applied in LIB is the strength and stability of solid electrolyte interphase (SEI) layer formed on the surface of Si anode. In the first part of this thesis, we report for the first time using hexafluorobenzene (HFB) to tackle the issue of rapid capacity fading during cycling process. When used as an electrolyte additive for Li-S cell, HFB preferably chelates with low-order lithium sulfides Li2S and Li2S2 and subsequently reacts and converts both into active aromatic sulfides: bis(pentafluorophenyl) disulfides and bis(pentafluorophenyl) polysulfides in-situ, thus facilitating the utilization of the electronically insulating Li2S and Li2S2 and improving the cycling stability of Li-S cell. The second part of this thesis is to determine the relationship between various electrochemical properties of Li-S battery and a series of lithium salt concentrations. According to the experimental results, choosing an appropriate salt concentration by balancing different properties the for each electrolyte to maximize their performances is more reasonable than using a certain salt concentration as a standard for all electrolytes and this is also an effective way to constrain the rapid capacity fading during cycling process. In the third part, the impact of the electrolyte solvation structure on the performance of Li-S battery was investigated using an electrolyte system containing various solvent ratios of dioxolane (DOL) and a nonafluorinated ether: 1,1,2,2-tetrafluoroethyl-2,2,3,3,3-pentafluoropropyl ether (TPE). The cell testing results indicate that increasing the ratio of TPE led to both a higher discharge capacity and a higher Coulombic efficiency, because lithium polysulfide shuttling issue is constrained when increasing the ratio of TPE in the electrolyte. In the fourth part, we introduce for the first time using 2,2,2-Trifluoroethyl methyl carbonate (FEMC) to optimize the Si anode. Based on the performance of LIBs, FEMC has potential to be an effective electrolyte co-solvent to protect Si anode due to the rich fluorine groups in its structure. When used as an co-solvent of all-fluorinated electrolyte, FEMC preferably passivates Si anode, helps the formation of a robust and resilient SEI layer, and alleviates the continuous reactions between Si and electrolyte and the delamination of electrode caused by the large volume change of Si during charging and discharging process. Therefore, FEMC co-solvent improves the electrochemical properties of LIB applying Si as anode. II Acknowledgements I would like to express my deep gratitude to my advisors, Prof. Yan Wang and Dr. Zhengcheng Zhang for their persistent supports and professional guidance. They discipline themselves with high standards and show me all the excellent qualities a researcher should have. They will be a role model I am following in my careers. I am honored to have Professor Richard D. Sisson, Professor Yu Zhong and Professor Qi Wen as committee members. Thanks for their help, encouragement, and guidance during my graduate studies. Special thanks to Professor Richard D. Sisson, who is always there and provides great help to me. His generosity and kindness make MSE department look like a big family for all of us. I want to thank Dr. Rachel Koritala and Dr. Zhenzhen Yang for their continuous help and technical guidance with SEM and XPS equipment. I also want to thank Dr. Quinton James Meisner, who helps me a lot on the organic chemistry and chemical characterization. Many thanks to Rita Shilansky, who treats me as a sincere friend, gave me generous help and constant care. I would like to thank all the collaborator and partners in this electrolyte optimization project. Tobias Glossmann from Mercedes-Benz Research & Development North America, Inc; Andreas Hintennach from Daimler AG (Mercedes-Benz Cars); Tomas Rojas, Ritu Sahore, Zhenzhen Yang, Paul Redfern, Anh Ngo, Larry A. Curtiss, from Argonne National Laboratory. I would like to thank my colleagues in Electrochemical Energy Laboratories of WPI and ANL, Zhangfeng Zheng, Qiang Wang, Bin Chen, Ruihan Zhang, Sungyool Bong, Jin Liu, Yubin Zhang, Mengyuan Chen, Xiaotu Ma, Yangtao Liu, Qing Yin, Azhari Luqman, Panawan Vanaphuti, Zifei Meng, Chao Shen, Dapeng Xu, Yadong Zheng, Jinzhao Fu, Jiajun Chen, Zeyi Yao, Yilun Tang; Quinton James Meisner, Sisi Jiang, Qian Liu, Zhangxing Shi, Johnson, Noah Mark, Bin Hu, III Jingjing Zhang, Jianzhong Yang, Haotian Yang, Mingfu He, Kewei Liu, Yuyue Zhao, Mengxi Yang, Lily, A Robertson, Lu Zhang, Chen Liao, who have been helping me a lot in the labs. I thank my parents and friends for their unconditional love and care. Without their support, I won’t achieve anything. I acknowledge the financial support of the Department of Energy and Mercedes-Benz Research & Development North America, Inc. Disclaimer This report was prepared as an account of work sponsored by an agency of the United States Government and Department of Energy and Mercedes-Benz Research & Development North America, Inc. Neither the Department of Energy and Mercedes-Benz Research & Development North America, Inc, the United States Government, nor any agency thereof, nor any of their employees, makes any warranty, expresses, implies, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof or those of Department of Energy and Mercedes-Benz Research & Development North America, Inc. IV Table of Content Abstract···································································································································· I Acknowledgements ···················································································································· III Table of Content ························································································································ V Chapter 1 Introduction of Lithium-Sulfur Battery and Si Electrode ······························································· 1 Chapter 2 Tackling the Capacity Fading Issue of Li-S Battery by a Functional Additive – Hexafluorobenzene ·········· 33 Chapter 3 A Systematic Research on the Relationship between Lithium Salt Concentration and Li-S Battery. ·········· 48 Chapter 4 Understanding the Impact of a Nonafluorinated Ether-Based Electrolyte on Li-S Battery ······················ 66 Chapter 5 Optimize the Lithium-Silicon Battery by a New Kind of All Fluorinated Electrolyte ···························· 83 Chapter 6. Summary ··················································································································· 98 Chapter 7. Future Work ·············································································································· 101 Chapter 8. Publications and Presentations ·························································································