Introduction
Electrochemical Impedance Spectroscopy, EIS, is a very powerful way to gain information
about electrochemical systems. It is often applied to new electrochemical devices used for
energy conversion and storage (ECS), including batteries, fuel cells, and super-capacitors.
EIS can be useful in all stages of the development of new devices, from initial evaluation of
half-cell reaction mechanisms and kinetics, to quality control of packaged batteries.
Increased use of ECS devices in higher power applications (such as electric vehicles) has led
to development of devices having very low impedance. Unfortunay for practitioners of EIS,
impedance of modern ECS devices is often so low that it cannot be easily or accuray
measured using laboratory EIS systems. Most commercial EIS system do not work well when
impedance is below 0.1 Ω.

This Application Note describes a series of EIS measurements made on a Li ion secondary
battery rated to have impedance below 500 μΩ at 1 kHz. Special techniques are used to
improve the accuracy and frequency range of this difficult measurement.
If you're new to EIS, you might want to read Gamry Instruments' Basics of EIS before
reading the rest of this Application Note. Information found in this introduction to EIS will not be repeated here.