Development of an Impedance Monitoring System for Rechargeable Lithium Batteries

Jorge Miguel Carmo Lourenço

Key information

Authors:

Jorge Miguel Carmo Lourenço (Jorge Miguel Carmo Lourenço)

Supervisors:

Luís Filipe Soldado Granadeiro Rosado (Luís Filipe Soldado Granadeiro Rosado); Pedro Miguel Pinto Ramos (Pedro Miguel Pinto Ramos)

Published in

December 6, 2024

Abstract

Due to the excellent energy and power density of lithium-ion batteries compared to other alternatives, the study of their characteristics has become increasingly relevant. The state-of-charge and state-of-health of batteries are closely related to their impedance, which can provide valuable information about their performance and longevity. This work presents the design, testing, and validation of an embedded system capable of performing impedance measurements using the Electrochemical Impedance Spectroscopy method on lithium-ion batteries. The system generates a multiharmonic stimulus that contains frequencies covering a range between 50 mHz and 1 kHz, at which the battery impedance is measured. The Goertzel algorithm is used to calculate the frequency components of the voltage and current signals, given that Coherent sampling is assured. This architecture reduces memory requirements as the samples are discarded after processing. A lithium-ion battery is subjected to multiple impedance measurements at different states of charge and health, allowing for a complete characterization of it's operation. Based on the obtained data, an equivalent electrical model is used to accurately describe the tested cell. The parameters of this model are correlated with variations in state-of-charge and state-of-health, providing a platform for future implementation of algorithms to estimate such states, based on impedance measurements.