Conduction in Multiphase Particulate/Fibrous Networks

Abstract

Several promising Li-ion battery technologies incorporate nanoarchitectured carbon networks, typically in the form of whisker/particle blends bonded with thermoplastic binders to form the anodes. Degradation of these materials is currently a persistent problem, with damage presenting as blistering and/or delamination of the electrode. Both material composition and morphology play a role in these critical failure modes, and are explored in the present work as they affect conduction in practical battery materials. Lawrence Berkeley National Laboratories and the Institut de Recherche d’Hydro-Quebec supplied the materials studied in this work. Our present approach builds on our previous numerical work, incorporating real material morphology and careful selection of boundary conditions to reduce the numerical difficulties posed by singularities in the field solution, due to phase contrast, sharp corners, etc. In order to allow use of these models for various shapes of particles, we provide a few simple geometrical relations for calculation of total surface area for various morphologies of electrode materials. A four-point-probe technique was employed to obtain the experimental conductivities. Although the existence of contact resistance is well known, there is little literature regarding a technique to measure its value; here, we also present a method for quantifying it, assuming that the anode layer is comprised of two layers. Voltage functions for each layer are determined by enforcement of voltage continuity at the interfaces, current intensities at the inlet and outlet on both sides of interface, and assumption of zero voltage in the second layer as z→∞.z→∞. The four-point-probe technique is suitable for the electrode materials tested, offering reasonable experimental precision in a simple setup. The results of this study offer some insight into the design of active materials. The model shows applicability to a wide variety of materials, including those comprised of fibers, particles, and flakes. Comparisons among simulation predictions and real material conductivities showed very good agreement. An obvious subject of future work is combined electrochemical, conduction, and mechanical modeling of these materials. © 2003 The Electrochemical Society. All rights reserved.