EIS Measurement of a Very Low Impedance Lithium Ion Battery

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. Unfortunately for practitioners of EIS, impedance of modern ECS devices is often so low that it cannot be easily or accurately measured using laboratory EIS systems. Most commercial EIS system do not work well when impedance is below 0.1 ?. This Application Note describes a series of EIS measurements made on a Li ion secondary battery rated to have impedance below 500 μ? 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.