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 We also discuss the local current density when lithium ions are withdrawn from the electrode, and illustrate the importance of a moving reference frame for defining ionic flux.