The impedance response of a porous electrode composed of intercalation particles

A mathematical model is developed to describe the impedance response of a p orous electrode composed of spherical intercalation particles. The model co nsiders a porous electrode without solution-phase diffusion limitations. Th e model is developed by first deriving the impedance response of a single i ntercalation particle, obtained by solving a set of governing equations whi ch describe charge-transfer and double-layer charging at the surface, solid -phase diffusion inside the particle, and an open-circuit potential which v aries as a function of intercalant concentration. The model also considers the effect of an insulating film surrounding the particle. The governing eq uations are linearized to take advantage of the small amplitude of the pert urbing current in impedance analysis. Once the impedance of a single partic le 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 comp osed. The model can be used to examine the effect of physical properties an d particle-size distributions in the porous electrode, and the usefulness o f impedance analysis to measure solid-phase diffusion coefficients is scrut inized. (C) 2000 The Electrochemical Society. S0013-4651(99)12-086-X. All r ights reserved.