Low Frequency Li-Ion Battery Impedance Measurements Using Broadband Excitations With Optimized Current Profiles

Abstract

Lithium-ion (Li-ion) batteries are widely used in applications ranging from transportation to grid-connected energy storage, where effective operation depends on accurate monitoring of the battery state through parameters such as state-of-health (SOH) and remaining useful life (RUL). Internal impedance is a powerful indicator of these parameters, and the low-frequency region of the impedance spectrum is particularly informative because it reflects slow electrochemical and degradation processes that strongly influence battery aging. However, low-frequency measurements are traditionally difficult due to long test durations and charge accumulation. Recent studies have shown that broadband excitation methods can greatly shorten measurement time, enabling practical online impedance estimation. This work presents a computer-optimized broadband sequence design specifically tailored to overcome the challenges of low-frequency impedance measurement, and experimentally validates the proposed excitation on a commercial Li-ion cell, demonstrating its potential for improved battery state assessment.