Negative Diffusion Coefficients, the Pesko Condition, and Performance of Polymer Electrolytes for Lithium Batteries

Negative Diffusion Coefficients, the Pesko Condition, and Performance of Polymer Electrolytes for Lithium Batteries

Abstract

The need for creating safe electrolytes for lithium batteries is significant given the continued safety problems associated with current lithium-ion batteries.  Nonflammable polymer electrolytes offer a possible solution but the rate of lithium ion transport is too low for practical applications.  In this talk, I will discuss some of the fundamental factors that limit ion transport in polymers.  In all electrolytes, the current generated at steady state is governed by the applied potential.  This relationship, which one might call a modified Ohm’s Law.  A crucial ingredient in Ohm’s Law for a material with two charged carriers is a “condition” that my PhD student Danielle Pesko arrived at.  I call it the Pesko condition.  We use this condition to calculate the maximum current that can be passed through a polymer electrolyte.

One approach for improving upon the energy density of rechargeable lithium-ion batteries is to replace the graphite negative electrode by lithium metal.  We discuss the local current density (or ionic flux) at a lithium electrode when lithium ions are delivered to it and through polymer electrolyte.  We also discuss the local current density when lithium ions are withdrawn from the electrode, and illustrate the importance of a moving reference frame for defining ionic flux.

Speaker

Nitash Balsara
Nitash Balsara is a Senior Faculty Scientist in the Materials Sciences Division at LBNL and The Charles W. Tobias Professor in Electrochemistry in the Chemical and Biomolecular Engineering Department at UC Berkeley. His research is based on soft microstructured materials such as block copolymer melts, polymer microemulsions, and colloidal suspensions. Principles of solid state physics provide a recipe for creating materials with low elastic moduli, G. For crystals, G=1/d where is the mean square displacement of the atoms, d is the lattice constant. In liquids, the mean square displacement is bounded only by the size of the container. Soft materials are thus characterized by periodic microstructures with relatively large lattice constants (d in the nanometer to micrometer range), fluctuations and disorder (the magnitude of can approach d), and liquid crystalline symmetry. We specialize in studying soft microstructures that self-assemble from the liquid state. The self-assembled nature of the structures that we study has important consequences. My program is concerned with the synthesis of such materials and the quantification of thermodynamic interactions that lead to microstructure formation. We are also developing experimental tools and the theoretical framework necessary to characterize the soft materials. We also use these materials to obtain a fundamental understanding of processes such as nucleation and flow alignment He did postdoctoral research at the Department of Chemical Engineering and Materials Science at the University of Minnesota, and at Exxon Research and Engineering Company in Annandale, New Jersey. In 1992, he joined the faculty of the Department of Chemical Engineering at Polytechnic University in Brooklyn, New York. He was promoted to associate professor in 1996 and professor in 1998. In 2000 he moved to the Department of Chemical Engineering at the University of California, Berkeley. In 2007, he founded Seeo Inc., a battery start-up in Berkeley, California. In 2009 he was promoted to a faculty senior scientist at LBNL. Dr. Balsara earned his bachelor's degree from the Indian Institute of Technology, his master's degree from Clarkson University and his PhD. degree from Rensselaer Polytechnic Institute.
Date/Time
Monday, September 28, 2020 - 10:00pm to Thursday, January 1, 1970 - 12:00am
Type
Seminar