Degradation Analysis of Lithium-ion Capacitors based on Electrochemical Impedance Spectroscopy

Lithium-ion capacitors (LICs) are utilized in various energy storage applications due to their wide operating temperature range, extended lifecycle, and higher power capability than lithium-ion batteries (LIBs). Understanding LIC degradation behavior is necessary for ensuring system reliability, performance, and lifetime. Unlike traditional methods, electrochemical impedance spectroscopy (EIS) allows real-time and direct impedance measurements of LIC over time. Therefore, this paper examines the degradation trends of LICs using the EIS technique, intending to estimate the state of health (SOH) throughout aging. Thus, experiments were conducted on five LICs subjected to various temperature conditions and charging/discharging C-rates to achieve this objective. In addition, this work specifically investigates the effect of these variables on the degradation behavior of LICs and the utilization of EIS as a diagnostic tool. However, The research reveals critical insights into how temperature and C-rates influence the SOH of LICs by monitoring the impedance changes. The experimental findings indicate that degradation is more pronounced at higher temperatures and lower C-rates, highlighting the importance of these factors in LIC lifetime. Therefore, this work provides valuable information and concepts for online LIC SOH estimation and diagnostics, particularly in electric city bus applications where reliability and lifetime are essential factors. Accurate monitoring and prediction of LIC SOH in real-time is crucial for optimizing performance and extending the lifetime of energy storage systems. This research contributes to the development of a more robust SOH estimation for urban transportation.