(7fl) Engineering the Next-Generation of Electrochemical Energy Storage

Kevin W. Knehr, Princeton University

2^nd Year Postdoctoral Research Associate

Research Interests:

Batteries are complex, multidisciplinary, electrochemical energy storage systems that are crucial for powering our society. The increasing demand for better batteries across a diverse range of applications (e.g., wearable tech, smartphones, electric vehicles, and grid-level storage) can only be met through the development of next-generation batteries employing new chemistries, new materials, and new designs. Identifying strategies for developing better batteries requires an understanding of the complex, coupled processes associated with mass transfer, reaction kinetics, and thermodynamics occurring within these systems. The combination of electroanalytical chemistry, materials characterization, continuum-level modeling, and engineering design offers a unique set of tools which can identify the performance limiting processes in batteries and provide solutions for enhancing the performance of next-generation systems.

Teaching Interests:

My objective as an educator is to have a heavy involvement with the undergraduate curriculum while maintaining a healthy research laboratory devoted to training the next generation of doctoral researchers. As an educator of undergraduates, I plan on leveraging my background as an electrochemical engineer to demonstrate how the fundamentals of chemical engineering (e.g., thermodynamics, reaction kinetics, transport, and engineering design) intersect in real-world applications, like batteries. To accomplish this, I am prepared to teach any of the chemical engineering core courses. In addition, I am interested in establishing an elective course in electrochemical engineering based on my Ph. D. adviser’s text book, which will contain a chapter on batteries I am helping to develop. As a mentor of graduate students, I anticipate a healthy laboratory of 4 to 6 Ph. D. students that I can personally train as electrochemical researchers. I believe direct involvement in all my students’ projects is important to cultivate the best research mindsets and to develop sound research practices.

Postdoctoral Project: “Development of a Minimal Architecture Zinc-Bromine Battery for Low Cost Electrochemical Energy Storage”

Under supervision of Daniel A. Steingart, Department of Mechanical and Aerospace Engineering, Andlinger Center for Energy and the Environment, Princeton University

Ph.D. Thesis: “Identification, Characterization, and Mitigation of the Performance Limiting Processes in Battery Electrodes”

Under supervision of Alan C. West, Department of Chemical Engineering, Columbia University

Research Experience:

My academic training has been rooted in the use of electrochemical theory, engineering, and design to probe the mechanisms controlling battery performance. As a result of my investigations into several different battery technologies, I have developed skillsets in both experimental characterization and theoretical modeling of complex electrochemical systems. For example, in one project (which I conducted as an NSF-GRFP fellow), I coupled in situ, synchrotron X-ray techniques at Brookhaven National Laboratory with electroanalytical methods to understand and control the growth of lead-sulfate crystals in lead-acid batteries. In another project, I used continuum level modeling to probe the mass transport limitations across multiple length scales (nm to cm) in lithium-ion batteries containing nanosized materials. During my time as a postdoc, my main focus has been on the investigation and advancement of a novel, membrane-free, zinc-bromide battery. To accomplish this, I have employed diagnostic techniques using microcontrollers and electroanalytical methods to understand the sources of efficiency loss and to study approaches for improving the lifetime, efficiency, and energy density of the system.

In addition to many skillsets, the multidisciplinary nature of batteries has provided experience in many research areas, including: chemistry, materials science, and of course, chemical engineering. Furthermore, the majority of my work during by Ph.D. involved close collaboration with synthetic chemists and beamline scientists at Brookhaven National Laboratory and Stony Brook University as a result of a DOE-Energy Frontier Research Center involving eight partner institutions. These collaborations have yielded invaluable training on the management, organization, and execution of large, multidisciplinary research projects.

Teaching Experience:

Along with my academic training, I have had several opportunities to enrich my abilities as an educator. In a formal setting, I have served as a teaching assistant and a guest lecturer. Additionally, I am involved in writing a chapter on batteries for my Ph.D. adviser’s text book: Electrochemistry and Electrochemical Engineering: An Introduction. In an informal setting, I have been a mentor to six undergraduate, one M. S. and five Ph. D. students throughout my career. I have also had the opportunity to work with middle school students through an outreach program I helped to develop as the President and Outreach Chair of the Chemical Engineering Graduate Organization at Columbia University. The program targets under-represented minorities in STEM, and consists of in-class activities and science fair projects at Frederick Douglass Academy II, a middle school in Harlem, NY.

Future Directions:

As a faculty member, I would like to continue on the path of characterizing and mitigating the performance limiting processes in current battery technologies and advancing novel battery systems and designs, which are tailored to modern applications. I am particularly interested in three main thrusts: a) development of electrochemical models for predicting and understanding battery degradation, b) advancement of batteries uniquely designed for the electric grid, where only cost and lifetime are the key design constraints, and c) investigation of the system-level performance of new, high-capacity materials that are being researched for portable applications. My current expertise in electrochemical theory, electroanalytical methods, and continuum-level modeling provides a useful framework for advancing new battery technologies because these tools make it possible i) to identify and mitigate the “rate-limiting” processes that are most detrimental to the performance of a specific battery chemistry and ii) to analyze the trade-offs associated with system-level design.

My overall approach is to leverage a deep understanding of electrochemical theory to develop experimental approaches and continuum-level simulations which probe and explain the underlying mechanisms controlling the performance of electrochemical systems. Therefore, my future lab will have both experimental and theoretical components. In addition, I anticipate close ties to collaborators which have access to advanced characterization techniques (e.g., at national laboratories) that can provide supporting information, especially on the evolution of materials properties within these electrochemical system.

Selected Publications (21 in total, 2 in preparation):

Shaurjo Biswas, Aoi Senju, Robert Mohr, Thomas Hodson, Nivetha Karthikeyan, Kevin W. Knehr, Andrew Hsieh, Xiaofeng Yang, Bruce E. Koel, and Daniel A. Steingart, “Minimal Architecture Zinc-Bromine Battery for Low Cost Electrochemical Energy Storage,” Energy & Environmental Science, 10, 114-120 (2017). DOI: 10.1039/C6EE02782B

K. W. Knehr, Christina A. Cama, Nicholas W. Brady, Amy C. Marschilok, Kenneth J. Takeuchi, Esther S. Takeuchi, and Alan C. West “Simulations of Lithium-Magnetite Electrodes Incorporating Phase Change,” Electrochimica Acta, 238, 384-396 (2017). DOI: 10.1016/j.electacta.2017.04.041

K. W. Knehr and Alan C. West, “Theoretical Considerations for Improving the Pulse Power of a Battery through the Addition of a Second Electrochemically Active Material,” Journal of the Electrochemical Society, 163, A1576-A1583 (2016). DOI: 10.1149/2.0621608jes

K. W. Knehr, Nicholas W. Brady, Christina A. Cama, David C. Bock, Zhou Lin, Christianna N. Lininger, Amy C. Marschilok, Kenneth J. Takeuchi, Esther S. Takeuchi, and Alan C. West, “Modeling mesoscale transport of lithium-magnetite electrodes using insight from discharge and voltage recovery experiments,” Journal of the Electrochemical Society, 162, A2817-A2826 (2015). DOI:10.1149/2.0961514jes

K.W. Knehr, Christopher Eng, Jun Wang, and Alan C. West, “Transmission X-Ray Microscopy of the Galvanostatic Growth of Lead Sulfate on Lead: Impact of Lignosulfonate,” Electrochimica Acta, 168, 346-355 (2015). DOI: 10.1016/j.electacta.2015.04.022

K. W. Knehr, Christopher Eng, Yu-chen Karen Chen-Wiegart, Jun Wang, and Alan C. West, “In situ transmission x-ray microscopy of the lead sulfate film formation on lead in sulfuric acid,” Journal of the Electrochemical Society,162, A255-A261 (2015). DOI: 10.1149/2.0141503jes

K. W. Knehr and E. C. Kumbur, “Role of convection and related effects on species crossover and capacity loss in vanadium redox flow batteries,” Electrochemistry Communications, 23, 76-79 (2012). DOI: 10.1016/j.elecom.2012.07.008

K.W. Knehr, Ertan Agar, C. R. Dennison, A. R. Kalidindi, and E. C. Kumbur, “A transient vanadium flow battery model incorporating vanadium crossover and water transport through the membrane,” Journal of the Electrochemical Society, 59, A1446-A1459 (2012). DOI: 10.1149/2.017209jes

K. W. Knehr and E. C. Kumbur, “Open circuit voltage of vanadium redox flow batteries: discrepancy between models and experiments,” Electrochemistry Communications, 13, 342-345 (2011). DOI: 10.1016/j.elecom.2011.01.020

Book Chapter:

“Batteries: Operation and Design,” in Electrochemistry and Electrochemical Engineering: An Introduction, Alan C. West, in progress.

Successful Proposals: NSF-GRFP Fellowship (2012-2016), NDSEG Fellowship awardee (Declined).