Distribution of Relaxation Times (DRT): an introduction Battery – Application Note 60

Abstract

DRT is a tool that can be used to help interpreting impedance data. This note introduces the theoretical basis of this method as well as the advantages and limitations compared to direct electrical equivalent circuit modeling.

Introduction

Electrochemical Impedance Spectroscopy (EIS) is used to identify the physical characteristics of a system. The method is to model the system using what is called an electrical equivalent circuit, where each element of the circuit is supposed to correspond to a physical characteristic of the system under study. Fitting the impedance data using an electrical model gives access to the values of the elements and hence of the physical characteristics, such as for instance time constants. The choice of an electrical circuit requires prior knowledge of the impedance of each element and this is why impedance can be considered difficult to use at first. DRT is an analysis method that turns impedance data that are a function of the frequency into a distribution of the time constants involved in the considered system. DRT can be considered as a tool to help to find an equivalent circuit that should be used to fit impedance data. In this note, we will present the main principles behind this analysis and show the various tools available to perform it. We will then present some results obtained that will illustrate the advantages and the interest of this method and finally evoke some of its limitations.

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