Investigation of Molten Salt Electrolytes for Low-Temperature Liquid Metal Batteries
Total Page：16
File Type：pdf, Size：1020Kb
Investigation of Molten Salt Electrolytes for Low-Temperature Liquid Metal Batteries by Brian Leonard Spatocco B.S., Materials Science and Engineering Rutgers University, 2008 M.Phil., Micro- and Nanotechnology Enterprise University of Cambridge, 2009 Submitted to the Department of Materials Science and Engineering in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy at the MASSACHUSETTS INSTITUTE OF TECHNOLOGY September 2015 © 2015 Massachusetts Institute of Technology. All Rights Reserved Author ………………………………………………………………………… Department of Materials Science and Engineering August 7, 2015 Certified and Accepted by …..……………………………………………………………………... Donald R. Sadoway John F. Elliot Professor of Materials Chemistry Thesis Supervisor Chair, Department Committee on Graduate Students 1 2 Investigation of Molten Salt Electrolytes for Low-Temperature Liquid Metal Batteries by Brian Leonard Spatocco Submitted to the Department of Materials Science and Engineering on August 14, 2015, in partial fulfillment of the requirements for the degree of Doctor of Philosophy Abstract This thesis proposes to advance our ability to solve the challenge of grid-scale storage by better positioning the liquid metal battery (LMB) to deliver energy at low levelized costs. It will do this by rigorously developing an understanding of the cost structure for LMBs via a process- based cost model, identifying key cost levers to serve as filters for system down-selection, and executing a targeted experimental program with the goal of both advancing the field as well as improving the LMB’s final cost metric. Specifically, cost modelling results show that temperature is a key variable in LMB system cost as it has a multiplicative impact upon the final $/kWh cost metric of the device. Lower temperatures can reduce the total cost via simultaneous simplifications in device sealing, packaging, and wiring. In spite of this promise, the principal challenge in reducing LMB operating temperatures (>400°C) lies in identifying high conductivity, low-temperature electrolytes that are thermally, chemically, and electrochemically stable with pure molten metals. For this reason, a research program investigating a promising low-temperature binary molten salt system, NaOH-NaI, is undertaken. Thermodynamic studies confirm a low eutectic melting temperature (219°C) and, together with the identification of two new binary compounds via x-ray diffraction, it is now possible to construct a complete phase diagram. These phase equilibrium data have then been used to optimize Gibbs free energy functions for the intermediate compounds and a two- sublattice sub-regular solution framework to create a thermodynamically self-consistent model of the full binary phase space. Further, a detailed electrochemical study has identified the electrochemical window (>2.4 V) and related redox reactions and found greatly improved stability of the pure sodium electrode against the electrolyte. Results from electrochemical studies have been compared to predictions from the solution model and strong agreement supports the physicality of the model. Finally, a Na|NaOH-NaI|Pb-Bi proof-of-concept cell has achieved over 100 cycles and displayed leakage currents below 0.40 mA/cm2. These results highlight an exciting new class of low-melting molten salt electrolytes and point to a future Na- based low-temperature system that could achieve costs that are 10-15% less than those of existing lithium-based LMBs. Thesis Supervisor: Professor Donald Robert Sadoway Title: John F. Elliot Professor of Materials Chemistry 3 4 This work is dedicated to my parents, Robin and Leonard Spatocco, who have given me all their love and asked for nothing but my happiness in return. This is but a small thank you. 5 6 Acknowledgements It is with a profound sense of gratitude that I acknowledge my great fortune and privilege in having been surrounded by some of the most passionate people along the many phases of my life. This work is a direct product of this lucky confluence of family, friends, and mentors and as a result is not a work I can claim full ownership over. In fact, a list of those to whom thanks are owed would likely stretch longer than the work itself. For this reason, this section’s listing of supporters work will be necessarily incomplete. I am so fortunate to have found a mentor and advisor in Professor Sadoway. Great science requires vision, method, and hard work. The latter two are often found in research here at MIT. The former, however, is far more rare. Don has shown me what it means to bring vision to a grand challenge. Specifically, asking the right questions, admitting the sometimes unusual answers, and being confident when others may not agree with your initial conclusions. I am forever grateful for this model of intellectual leadership. Professor Sadoway’s ability to inspire not only drove ground-breaking research but also attracted a peerless team of fellow researchers. Much like the scientific dream teams of former eras, ours was a group replete with experience, intelligence, and passion. Our postdoctoral researchers taught me everything I know about research success and failure, and everything in between. They were also great friends. I am deeply indebted to Dane Boysen, Hojong Kim, Brice Chung, Takanari Ouchi, Paul Burke, Guillaume Lambotte, Huayi Yin, Kai Jiang, and Kangli Wang. I’ve also had the great fortune to transit through the materials science doctoral program with some of the most fun and inspiration fellow graduate students in the Sadoway Group and DMSE at-large. Jocelyn Newhouse, Salvador Barriga, John Rogosic, Sophie Poizeau, and Dave Bradwell all made the hardest days passable and the best days possible. I am indebted for their partnership and comradery as we worked to invent for the future. Outside of the group, I recall the dark days of quals, the happy holiday dinners, and everything in between with other friends in the department. Specifically, Max Solar, Neil Patel, Adam Jandl, and Dan Harris served as the most reliable supports during shaky times. MIT has also afforded me the unmatched opportunity to grow my leadership and management style. Over the last six years I’ve had the chance to lead and learn from those around me. At Sidney Pacific graduate residence I am grateful for having learned from George Lan, Holly Johnson, George Tucker, Ahmed Helal, Pierre-Olivier LePage, Boris Braverman, William Li, Chelsea He, Amy Bilton, Po- Ru Loh, Tim Curran, and Rosaria Chiang. In addition to creating a fun place to live I also had the chance to fight for student housing and welfare issues with Maokai Lin, Randi Cabezas, and Nathaniel Schafheimer. More than any other position at MIT, my time in the Graduate Student Council executive officer team has helped me grow and mature. Much of this is thanks to mentors in MIT’s administration but perhaps the greatest contributors were the students with whom I had the great fortune to share the burden. Namely, Aalap Dighe, Bomy Lee Chung, and Eric Victor have given more to me than I can repay. The incredible impact we had in that year is principally thanks to our team’s trust and cohesivity. I would be unsurprised if our group remains the most effective leadership team I’ve ever been a part of even as I transition to the working world. 7 A final group of friends I wish to recognize are those I have lived and worked with on projects external to MIT. Stephen Morgan has been a constant positive force in my life. He has taught me the value of loyalty to one’s friends. George Chen has been an inspirational source of courage in my life. George has shown me the value of learning outside my comfort zone. Kendall Nowocin has been an exemplar of what family can and should mean in my life. He has shown me how and why to cherish those around us. Javier Sanchez-Yamagishi has taught me the value of persistence and hard work unlike any other person. You’re my role model for how I should set my goals and raise my sights throughout my life. And finally, Kelli Xu has reinvigorated my love of life and the world around me. As my partner you’ve exposed me to new experiences, challenged my assumptions, and helped me be a more authentic person. The last group of people I am forever indebted to, and to whom this work is dedicated, is my family. My mother Robin Spatocco and Leonard Spatocco have spent their lives giving me every chance and support I could ask for and asked only for my happiness in return. They did so with a depth of love I can only hope to bring to my future family. You’ve given me a wonderful life and an even better example to carry forward. You are both incredible people. Similarly, to my brother Peter Spatocco, your humility in the midst of such success inspires me. I can’t wait to grow older with you and your family in my life. 8 Contents Acknowledgements ......................................................................................................................... 7 Table of Figures ............................................................................................................................ 11 Chapter 1 - Introduction ................................................................................................................ 15 1.1 The Winds of Change .......................................................................................................... 15 1.2 Cost is King ......................................................................................................................... 17