Non-Invasive Diagnosis of Aged Lithium-Ion Capacitors using Distribution of Relaxation Times

This study explores the application of Distribution of Relaxation Times (DRT) analysis, combined with Electrochemical Impedance Spectroscopy (EIS), to evaluate the aging behavior of Lithium-ion Capacitors (LiCs). While DRT analysis has previously been applied almost exclusively to lithium-ion batteries, it has not been applied to supercapacitor technologies such as LiCs. Although EIS is widely used to study Energy Storage Systems (ESS), it often struggles to provide a detailed description of the underlying electrochemical processes. In this work, EIS data collected from LiCs at various States of Charge (SoC) were transformed into DRT profiles, enabling clearer identification of charge-transfer, diffusion, and other key processes. The extracted parameters were then used to construct a multi-branch impedance model, incorporating a Constant Phase Element (CPE) to represent diffusive behavior. The main contribution of this study is demonstrating, for the first time, the use of DRT analysis on LiCs, highlighting its value as a non-invasive, high-resolution diagnostic tool that can support the optimization of LiCs management systems.