The impedance response of a porous electrode composed of intercalation particles

A mathematical model is developed to describe the impedance response of a porous electrode composed of spherical intercalation particles. The model considers a porous electrode without solution-phase diffusion limitations. The model is developed by first deriving the impedance response of a single intercalation particle, obtained by solving a set of governing equations which describe charge-transfer and double-layer charging at the surface, solid-phase diffusion inside the particle, and an open-circuit potential which varies as a function of intercalant concentration. The model also considers the effect of an insulating film surrounding the particle. The governing equations are linearized to take advantage of the small amplitude of the perturbing current in impedance analysis. Once the impedance of a single particle is determined, this result is incorporated into a model which describes a porous electrode limited by ohmic drop in the solution and solid phases, and by the impedance of the particles of which the porous electrode is composed. The model can be used to examine the effect of physical properties and particle-size distributions in the porous electrode, and the usefulness of impedance analysis to measure solid-phase diffusion coefficients is scrutinized. (C) 2000 The Electrochemical Society. S0013-4651(99)12-086-X. All rights reserved.