How to interpret lower frequencies impedance in batteries (EIS low frequency diffusion) Battery – Application Note 61

Abstract

The lower frequencies part of the impedance is of interest as it can be used to derive critical characteristics such as the diffusion constant of the intercatalated species in a given material. This note explains in which conditions this parameter can calculated from impedance data.

Introduction

Impedance measurements can be used to monitor and control the degradation of the performance of a battery over cycling. Measurements are usually performed at higher frequencies to determine the internal resistance of an element [1-4]. However, in the case of batteries involving intercalation of species, at lower frequencies, impedance measurements can also prove to be useful as in certain conditions it is possible to extract the diffusion coefficient of the intercalated species. This quantity is also of great importance in the process of battery materials quality optimization and monitoring [3-6]. This application note shows on a few examples how the impedance data at lower frequencies can be fitted and the method to extract useful experimental data by selecting the most appropriate element for the Equivalent Circuit (EC).

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