Movement of Neutral Molecules Under Electric Fields and Relevance to Rechargeable Batteries
Nitash P. Balsara
Charles W. Tobias Professor in Electrochemistry
University of California, Berkeley
Friday, November 21, 2025
3:00 p.m., 66-110, (2:30 p.m. Reception)
Massachusetts Institute of Technology
Abstract:
In the presence of applied electric fields, it is natural to focus on the movement of charged ions. In this talk however, I will focus on the movement of neutral “solvent” molecules used to dissolve the ions inside batteries. Any energy used to move solvent molecules is wasted, and thus it is important to understand how they move in electric fields. In our case, the solvent is a polymer; I believe that polymer electrolytes will play an essential role in enabling next-generation rechargeable batteries. My journey began when I learned about the continuity equation in my first transport phenomena course as an undergraduate student. I will describe how the continuity equation changes in the presence of an electric field. While ion velocities can be inferred from current-voltage measurements, there were no well-established approaches for measuring velocities of neutral molecules in batteries. My group (and others) have recently developed experimental approaches for accomplishing this. Surprisingly, the field-induced velocity of uncharged long polymer chains is comparable to that of the ions. Experimental results and theoretical predictions are compared without resorting to adjustable parameters. In addition to continuum-scale experiments, I will describe the results of quasi-elastic neutron scattering experiments which enable the study of the motion of polymer segments in the vicinity of ions on the Angstrom length scale. These measurements and computer simulations on the same length scale provide insight into the underpinnings of continuum transport. I will conclude by describing the connection between our work on polymer motion and the continuing push to commercialize all-solid rechargeable batteries for electric vehicles and other energy-related applications.
Professor Hottel worked in the seemingly unrelated field of radiative heat transfer in complex geometries. He understood the complexity of the problem, especially if gasses such as CO2 were between them. He had the foresight to develop simple approaches that allowed engineers like me to compute energy transfer rates; I learned about the Hottel crossed string method in the same transport phenomena course described above. His work serves as an inspiration as I prepare this lecture.
Bio
Nitash P. Balsara is a chemical engineer with a bachelor’s degree from the Indian Institute of Technology in Kanpur, India, a master’s degree from Clarkson University, and a PhD from Rensselaer Polytechnic Institute. This was followed by two post-doctoral appointments at the University of Minnesota and the Exxon Research and Engineering Company. In 1992, he joined the faculty of Department of Chemical Engineering at Polytechnic University in Brooklyn, New York. In 2000 he moved to Berkeley to join the faculty at the Department of Chemical Engineering at the University of California and to join Lawrence Berkeley National Laboratory as a faculty scientist. He has managed to hang on to both jobs. In addition, he cofounded two battery start-ups with his students and collaborators, Seeo and Blue Current.