Computer simulations of the impedance response of lithium rechargeable batteries

A mathematical model is developed to simulate the impedance response of a wide range of lithium rechargeable battery systems. The mathematical model is a macroscopic model of a full-cell sandwich utilizing porous electrode theory to treat the electrode region and concentrated solution theory for transport processes in solution. insertion processes are described with charge-transfer Kinetic expressions and solid-phase diffusion of lithium into the active electrode material. The impedance model assumes steady-state conditions and a linear response with the perturbation applied about the open-circuit condition for the battery. The simulated impedance response of a specific system, the lithium-polymer cell Li\PEO18LiCF3SO3\LiTiS2, is analyzed in more detail to illustrate several features of the impedance behavior. Particular attention is paid to the measurement of solid-phase lithium-ion diffusion coefficients in the insertion electrodes using impedance techniques. A number of complication that can lead to errors in diffusion-coefficient measurements based on impedance techniques are discussed. (C) 2000 The Electrochemical Society. S0013-4651(98)11-056-X. All rights reserved.