Towards Accurate Battery Health Estimation Using EIS with SoC-Sweep Analysis

Sammanfattning

This study explores how Electrochemical Impedance Spectroscopy (EIS) can be used to evaluate the health of lithium-ion battery cells. Central to the thesis is the use of a newly developed measurement system called Clarity, created by the company Batixt. This tool enables significantly faster and more detailed EIS measurements than existing commercial systems, making it possible to perform the in-depth analysis presented in this work. The focus of the thesis is on identifying the causes of cell degradation and understanding how specific degradation mechanisms influence the EIS response. To achieve this, several methods of analyzing EIS data are investigated. These include assessing whether the data can be accurately modeled and determining if the resulting model parameters provide insights into internal cell phenomena. The behavior of cells across different voltage levels is also examined, such as variations in charge draw. One particularly useful analysis method employed is a simple geometric approach involving the calculation of curvature radius along the EIS curve, enabling straightforward comparisons between multiple curves to observe shape deviations. Additionally, cells from a battery pack were analyzed to identify signs of degradation using the EIS method, demonstrating its applicability in practical scenarios. In parallel, a targeted cycling procedure was developed to intentionally induce specific degradation mechanisms within the cell.