A Comparative Study on the Various Aging Laws Governing Lithium-Ion Capacitor Cycling Aging

Lithium-ion Capacitors (LICs) are energy storage devices (ESDs) that combine the benefits of Lithium-Ion Batteries (LIBs) and Supercapacitors (SCs) by filling the gap between the low power densities of LIBs and the low energy densities of SCs. As an electrochemical device, LICs experience aging processes over their life, which is indicated by electrical performance losses. To predict performance degradation, aging models are developed. This study attempts to present a comparative analysis of the four capacitive evolution predictive mechanisms (aging laws) of an LIC over its cycle life under various operating conditions. To examine and recognize the aging behavior of LIC cells, the experimental data obtained from cycling aging of eight commercial 2100F LIC cells under different operating conditions, including temperature, C-rate, and cycling depth of discharge (DOD) are used. The four aging models namely the Langmuir model, SEI Layer formation model, decay model, and a heuristic model considered for this study, are identified using the least square error minimization algorithm and the experimentally obtained capacitance versus charge cycle data. The goodness of fit of these models is analyzed by calculating the R2 and RMSE values. On comparison, it is found that the Langmuir model is best suited for the cycle aging simulation of LIC and the main cause of LIC cycling aging is a reversible gas adsorption phenomenon.