EIS Quality Indicators: THD, NSD & NSR – Battery & Corrosion – Application Note 64

Abstract

Three quality indicators are available in EC-Lab® to quantitatively assess the quality and the validity of your EIS experiment: i) Total Harmonic Distortion quantifies the linearity of the response, ii) Non Stationary Distortion indicates the effect of time-variance and transient regime, finally iii) Noise to Signal Ratio ensures the signal is large enough compared to the measurement noise. Some results are given on the electrical circuit as well on a discharging battery.

Introduction

EIS is a powerful technique used to study an electrochemical system in a specific state and understand the nature of the reactions occurring at the interface. Usually, this technique is based on the analysis of the linear response of an electrochemical system submitted to a potential or current sinusoidal modulation. For an EIS experiment as defined above to be valid, the system under study should fulfill various requirements:

1. The system should be linear. A simple example of a linear system is a resistor [1].
2. The response of the system should not be transient ie. it should have reached a steady-state or permanent regime [2].
3. The values of the parameters defining the system should not be changing throughout the experiment. Impedance measurements on a time-variant system can lead to a wrong interpretation [3].
4. The system should be the same throughout the experiment. For example, a passive electrode that depassivates is not an adequate system

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