(6ed) Materials for Energy Storage Applications: Fundamental Insight for Rational Design and Development

Environmental challenges and economic forces are reshaping the way we generate and consume energy on a global scale. To keep up with the accelerating adoption of electric vehicles, allow for grid scale energy storage, and meet the demands of future electronic applications, new materials for high energy density batteries must be developed. Lithium ion batteries are presently the dominant form of energy storage used in consumer electronics and, recently, electric vehicles. However, high costs have prevented widespread deployment of lithium ion batteries for applications other than portable electronics, and the safety hazards of exothermic reactions associated with traditional materials during cell failure remain to be addressed. Therefore, strategies to enhance the mechanical and chemical stability of advanced electrode materials are key to their successful application in commercial batteries.

My future research will use insight gained from the study of charge transport processes and interfacial reactions/interactions to inform the design of new materials for energy storage applications.

Overall, the goal of my work will be to identify and understand molecular phenomena that can be utilized to design and develop materials to specifically address challenges related to enabling advanced battery chemistries. These new materials will pave the way for low cost and safe energy storage technology by stabilizing high energy density battery chemistries, replacing flammable liquid carbonate electrolytes, and enabling new form factors for batteries in advanced electronic applications. Using spectroscopic and electrochemical techniques and in situ characterization tools my research will answer questions regarding the solvation structure of ions in polymer and small molecule electrolytes for fast and selective lithium ion transport and the kinetics and mechanisms of electrochemical reactions related to advanced battery chemistries. Furthermore, I plan to utilize tools for automated experimentation and high throughput analysis to accelerate the materials discovery process. This research program builds on my combined expertise in materials synthesis, characterization of kinetic and transport properties, and electrochemical device fabrication gained through my graduate and postdoctoral research.

Graduate Research with Prof. Zhenan Bao at Stanford University

During my PhD studies I designed and synthesized new self-healing polymers and elastomers with a focus on specialized mechanical properties for improving the stability of lithium ion batteries (1). Silicon and lithium metal can store ten times more charge than the graphite used in commercial electrodes; however, silicon, due to its brittle nature and large volume expansion during lithiation, has poor cycling stability, while lithium metal suffers from significant side reactions, poor quality deposition, and the potential to form hazardous dendrites. Using a supramolecular self-healing polymer as the binder for a silicon microparticle electrode or coating on the lithium metal anode, I demonstrated improved cycling stability of these high capacity materials. As a binder, the self-healing polymer enables the electrode to heal after fracture of the silicon, and by identifying an optimal relaxation time to maximize cycling stability I found that the success of this self-healing electrode concept relies on a balance of stress relaxation and stiffness in the binder (2). Moreover, the self-healing polymer coating on lithium metal enabled dendrite free deposition at current densities as high as 5 mA cm^-2 (3). To understand this effect, I studied several carefully selected polymers with varied chemical and mechanical properties as coatings on the Li metal anode. Thermodynamic analysis of the lithium nucleation process identified the polymer dielectric constant and surface energy as two key descriptors of the polymer coating on lithium deposition (4). Furthermore, I explored the design and synthesis of elastic polymer networks that contained a combination of covalent and dynamic hydrogen bonding crosslinks for enhanced stress dissipation and improved toughness. I used these dynamic hydrogen bonds to create a self-healing elastomer that enabled the first demonstration of a low potential, high capacity electrode for stretchable lithium ion batteries based on a graphitic carbon/silicon composite foam electrode (5). Further development of this class of tough elastomers led to the creation of a highly resilient lithium ion conducting material able to elastically absorb as much energy as Kevlar based electrolyte materials while conducting lithium ions at the same order of magnitude as commercial separators (6).

Postdoctoral Research with Prof. Yang Shao-Horn at MIT

For my postdoctoral research, I am working in two areas related to understanding the mechanisms of electrochemical instability and dynamics of ion transport in small molecule and polymer electrolytes. First, I am using in situ characterization techniques to study the electrolyte decomposition reactions at the lithium metal interface in order to clearly identify the components of the solid electrolyte interphase (SEI), which strongly influences the cycling stability of lithium metal batteries, and the mechanism of its formation. The structure and composition of the SEI on lithium metal is poorly understood and there is great need to expand knowledge in this area to provide guidance for the development of new electrolytes and additives. Second, I am working as part of a large combined synthetic and computational effort to design and discover polymer electrolytes for Li-ion batteries. To aid in this work, I have led the development of an automated platform for fully integrated electrolyte formulation and testing. This high throughput tool allows for the accumulation of extremely large, high quality data sets required to enable machine learning methodologies for the computer-generated prediction and optimization of polymer electrolytes.

Teaching Interests:

As a teacher and mentor, I aim to provide students with the skills to clearly identify questions that interest them and the tools to answer those questions. During my PhD at Stanford University I was a teaching assistant for Polymer Chemistry and Micro and Nanoscale Fabrication Engineering where I gained experience preparing course materials and guiding student projects. In the laboratory, I have formally mentored 1 high school, 4 undergraduate, 2 Master’s, and 3 PhD rotation students at various times during my PhD and postdoctoral work. Additionally, I have worked with various programs at Stanford and MIT to promote improved access to higher education among students from underrepresented minority groups. With my undergraduate and graduate background in chemical engineering, I am able to teach core chemical engineering courses at any level, and I am particularly interested in teaching courses where I can combine chemical engineering principles with a molecular perspective. I am also excited about teaching or developing lecture and laboratory based courses in polymer sciences and electrochemistry.

Selected Publications:

1. Lopez, J.; Mackanic, D.G.; Cui, Y.; Bao, Z. Designing Polymers for Advanced Battery Chemistries. Nat. Rev. Mater. 2019, 4 (5), 312–330
2. Lopez, J.; Chen, Z.; Wang, C.; Andrews, S. C.; Cui, Y.; Bao, Z. The Effects of Cross-Linking in a Supramolecular Binder on Cycle Life in Silicon Microparticle Anodes. ACS Appl. Mater. Interfaces 2016, 8 (3), 2318–2324.
3. Zheng, G.*; Wang, C.*; Pei, A.*; Lopez, J.*; Shi, F.; Chen, Z.; Sendek, A. D.; Lee, H.-W.; Lu, Z.; Schneider, H.; Safont-Sempere, M. M.; Chu, S.; Bao, Z.; Cui, Y. High Performance Lithium Metal Anode with a Soft and Flowable Polymer Coating. ACS Energy Lett. 2016, 1 (6), 1247–1255. *equal contribution
4. Lopez, J.; Pei, A.; Oh, J. Y.; Wang, G.-J. N.; Cui, Y.; Bao, Z. Effects of Polymer Coatings on Electrodeposited Lithium Metal. J. Am. Chem. Soc. 2018, 140 (37), 11735–11744.
5. Sun, Y.*; Lopez, J.*; Lee, H.-W.; Liu, N.; Zheng, G.; Wu, C.-L.; Sun, J.; Liu, W.; Chung, J. W.; Bao, Z.; Cui, Y. A Stretchable Graphitic Carbon/Si Anode Enabled by Conformal Coating of a Self-Healing Elastic Polymer. Adv. Mater. 2016. 28 (12), 2455-2461. *equal contribution
6. Lopez, J.; Sun, Y.; Mackanic, D. G.; Lee, M.; Foudeh, A. M.; Song, M.-S.; Cui, Y.; Bao, Z. A Dual-Crosslinking Design for Resilient Lithium-Ion Conductors. Adv. Mater. 2018, 30 (43), 1804142.