University of Rhode Island DigitalCommons@URI Open Access Dissertations 2014 ANODE SOLID ELECTROLYTE INTERPHASE (SEI) OF LITHIUM ION BATTERY CHARACTERIZED BY MICROSCOPY AND SPECTROSCOPY Mengyun Nie University of Rhode Island, [email protected] Follow this and additional works at: https://digitalcommons.uri.edu/oa_diss Recommended Citation Nie, Mengyun, "ANODE SOLID ELECTROLYTE INTERPHASE (SEI) OF LITHIUM ION BATTERY CHARACTERIZED BY MICROSCOPY AND SPECTROSCOPY" (2014). Open Access Dissertations. Paper 202. https://digitalcommons.uri.edu/oa_diss/202 This Dissertation is brought to you for free and open access by DigitalCommons@URI. It has been accepted for inclusion in Open Access Dissertations by an authorized administrator of DigitalCommons@URI. For more information, please contact [email protected]. ANODE SOLID ELECTROLYTE INTERPHASE (SEI) OF LITHIUM ION BATTERY CHARACTERIZED BY MICROSCOPY AND SPECTROSCOPY BY MENGYUN NIE A DISSERTATION SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY IN CHEMISTRY UNIVERSITY OF RHODE ISLAND 2014 DOCTOR OF PHILOSOPHY DISSERTATION OF MENGYUN NIE APPROVED: Dissertation Committee Major Professor Brett Lucht Arijit Bose William Euler Nasser H. Zawia DEAN OF THE GRADUATE SCHOOL UNIVERSITY OF RHODE ISLAND 2014 ABSTRACT The surface reactions of electrolytes with the graphitic anode of lithium ion batteries have been investigated. The investigation utilizes two novel techniques, which are enabled by the use of binder-free graphite anodes. The first method, transmission electron microscopy (TEM) with energy dispersive X-ray spectroscopy, allows straightforward analysis of the graphite solid electrolyte interphase (SEI). The second method utilizes multi-nuclear magnetic resonance (NMR) spectroscopy of D2O extracts from the cycled anodes. The TEM and NMR data are complemented by XPS and FTIR data, which are routinely used for SEI studies. Cells were cycled with LiPF6 and ethylene carbonate (EC), ethyl methyl carbonate (EMC), and EC/EMC blends. This unique combination of techniques establishes that for EC/LiPF6 electrolytes, the graphite SEI is ∼50 nm thick after the first full lithiation cycle, and predominantly contains lithium ethylene dicarbonate (LEDC) and LiF. In cells containing EMC/LiPF6 electrolytes, the graphite SEI is nonuniform, ∼10−20 nm thick, and contains lithium ethyl carbonate (LEC), lithium methyl carbonate (LMC), and LiF. In cells containing EC/EMC/LiPF6 electrolytes, the graphite SEI is ∼50 nm thick, and predominantly contains LEDC, LMC, and LiF. The novel techniques as combinations of binder free graphite electrodes with Transmission Electron Microscopy (TEM) grids and D2O extraction allowed us to analyze SEI species efficiently and also can be applied in other systems. The investigation utilizes thoes novel techniques which are enabled by the use of binder free silicon (BF-Si) nano-particle anodes. The first method, Transmission Electron Microscopy (TEM) with Energy Dispersive X-ray Spectroscopy (EDX), allows straightforward analysis of the BF-Si solid electrolyte interphase (SEI). The second method, utilizes Multi-Nuclear Magnetic Resonance (NMR) spectroscopy of D2O extracts from the cycled anodes. The TEM and NMR data are complemented by XPS and FTIR data, which are routinely used for SEI studies. Coin cells (BF-Si/Li) were cycled in electrolytes containing LiPF6 salt and ethylene carbonate (EC) or fluoroethylene carbonate (FEC) solvent. Capacity retention was significantly better for cells cycled with LiPF6/FEC electrolyte than for cells cycled with LiPF6/EC electrolyte. Our unique combination of techniques establishes that for LiPF6/EC electrolyte, the BF-Si SEI continuously grows during the first 20 cycles and the SEI becomes integrated with the BF-Si nano-particles. The SEI predominantly contains lithium ethylene dicarbonate (LEDC), LiF, and LixSiOy. BF- Si electrodes cycled with LiPF6/FEC electrolyte have a different behavior; the BF-Si nano-particles remain relatively distinct from the SEI. The SEI predominantly contains LiF, LixSiOy and an insoluble polymeric species. The investigation of the interrelationship of cycling performance, solution structure, and electrode surface film structure has been conducted for electrolytes composed of different concentrations of LiPF6 in propylene carbonate (PC) with a binder free (BF) graphite electrode. Varying the concentration of LiPF6 changes the solution structure altering the predominant mechanism of electrolyte reduction at the electrode interface. The change in mechanism results in a change in the structure of the solid electrolyte interface (SEI) and the reversible cycling of the cell. At low concentrations of LiPF6 in PC (1.2 M), electrochemical cycling and cyclic voltammetry (CV) of BF graphite electrodes reveal continuous electrolyte reduction and no lithiation/delithiation of the graphite. The solution structure is dominated by + - solvent separated ion pairs (Li (PC)4//PF6 ) and the primary reduction product of the electrolyte is lithium propylene dicarbonate (LPDC). At high concentrations of LiPF6 in PC (3.0 - 3.5 M), electrochemical cycling and CV reveal reversible lithiation/delithiation of the graphite electrode. The solution structure is dominated by + - contact ion pairs (Li (PC)3PF6 ) and the primary reduction product of the electrolyte is LiF. ACKNOWLEDGMENTS First of all, I would like to thank my major professor as well as my Ph.D advisor Prof. Brett Lucht for his guidance, help and providing me with great atmosphere and great opportunities for doing research about lithium ion battery. It was an honor to work in this lab. Also I appreciate all the help provided by Prof. William Euler as Chemistry Department Chair and the helps from my other committee members. I would like to thank Prof. Bose, Heskett and Yang for reviewing my dissertation. I also would like to thank Dr. Abraham in Argonne National Lab for offering me opportunity to visit his lab and teaching me great knowledge in research. I am grateful to many collaborators Dr. Yanjing Chen, Dr. Swapnil Dalavi and Dr.Cao Cuong Nygen for helping and encouraging me during my study. My deepest gratitude is for University of Rhode Island for giving me the opportunity to finish my Ph.D study. I appreciate all people who company with me for almost five years in my lab. Finally, I would like to thank my mom and husband Guang to take care my life. I believe this achievement cannot complete without any one of you. v PREFACE This dissertation is written in manuscript format. There are five chapters in this dissertation. The first chapter is the main introduction of Lithium ion battery. From the second chapter to the fifth chapter are the manuscripts I have completed. The second chapter is one article already published in the Journal of Physical Chemistry, C and this article is the most read article in that month. The third chapter is also made of my published paper in Journal of Physical Chemistry, C. The fourth chapter is come from my third publication in the same journal (JPCC). The last chapter, chapter 5, is written as a manuscript will be submitted to the Journal of Electrochemical Society. vi TABLE OF CONTENTS ABSTRACT .................................................................................................................. ii ACKNOWLEDGMENTS ........................................................................................... v PREFACE .................................................................................................................... vi TABLE OF CONTENTS ........................................................................................... vii LIST OF TABLES ....................................................................................................... x LIST OF FIGURES .................................................................................................... xi CHAPTER 1. INTRDUCTION .................................................................................. 1 Overview .............................................................................................................. 1 Solid Electrolyte Interphase in Lithium ion Battery ............................................ 2 Reactions proposed for SEI formation ................................................................. 4 SEI Composition and Morphology ...................................................................... 5 Influence of SEI on battery performance ............................................................. 6 Conclusion ........................................................................................................... 7 Reference.............................................................................................................. 9 CHAPTER 2. STRUCTURE OF THE GRAPHITE ANODE SOLID ELECTROLYTE INTERPHASE IN LITHIUM ION BATTERIES .............................................................................................................. 11 Introduction ......................................................................................................... 12 Experimental Sections .......................................................................................... 15 Results and Discussion ......................................................................................... 18 Conclusions .......................................................................................................... 32 vii Reference............................................................................................................