Application notes 15 min read

Ohmic Drop Part III: Suitable use of the ZIR techniques (Ohmic drop & ZIR techniques) – Battery – Application Note 29

Latest updated: August 31, 2021

Abstract

ZIR is an ohmic drop determination technique that uses an impedance measurement at a single frequency. This frequency is generally a high frequency and can be changed by the user. When the impedance of the system has an inductance term due to wires in batteries, for instance, using high frequencies might lead to an error on the ohmic drop determination. The only way to determine this error is to perform a full EIS diagram

 

Introduction

As shown in Application note #28 [1], EIS measurements are a good way to determine the electrolyte resistance RΩ (or Ru for uncompensated resistance [2]). RΩ is defined as the solution resistance between the working electrode and the reference electrode plus any resistances in the working electrode itself, wires, etc. [2, 3]. ZFit tool of EC-Lab® or EC-Lab® Express software allows the user to calculate this RΩ value. Nevertheless, ZFit tool implies that the equivalent electrical circuit is known, which is sometimes not obvious. The aim of this note is to present the IR determination and compensation by impedance measurement technique (ZIR) and then how to determine RΩ value without using the ZFit tool. A part of this note will be dedicated to enlightening the limits of this technique for some systems.

 

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