Potentio or Galvano EIS – Battery – Application Note 49

Abstract

Bio-Logic Potentiostats-Galvanostats-ZRAs and battery cyclers are capable of performing EIS measurements under potentiostatic (apply potential, measure current) and galvanostatic (apply current, measure potential) control. As long as linearity, stability and causality criteria are fulfilled, both methods yield the same results. However, in many applications, especially energy-related, Galvano control allows determination of the cell impedance under a constant DC load. This note discusses precautions that have to be taken into account when setting up the experiment, as well as, artifacts that indicate problems with the experimental setup. In particular, running an experiment under load, by definition violates the stability criterion, therefore only the high and medium-frequency part of the spectrum can be rigorously analyzed (it takes little time to record, hence the system can be treated as quasi-stable).

Introduction

Electrochemical Impedance Spectroscopy (EIS) measurements are more often performed under potentio control than under galvano control. In most cases, the potentio and galvano modes are equivalent (PEIS or GEIS techniques, in EC-Lab® software). So performing the EIS measurements under potential or current control result in the same impedance diagrams. However, in certain conditions, one does not obtain the same results, typically when the system evolves during the measurement. In corrosion applications, e.g., the polarization resistance is often determined under potential control around open-circuit voltage (OCV). This is an appropriate approach if the corrosion potential does not change during the measurement. If the corrosion potential drift, the measurements performed at OCV could result in an anodic or cathodic potential respect to the true OCV. Under Galvano control, the desired zero-current condition is maintained throughout the recording, ensuring the measurement is performed at the true corrosion potential [1]. In battery applications, it would be interesting to determine the variation of internal resistance during discharge/charge. In this case, it could be also appropriate to use the galvano control in EIS measurements [2]

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