Analysis of Charge Redistribution During Self-discharge of Double-Layer Supercapacitors

Self-discharge is an important factor that severely affects the performance of double-layer supercapacitors. This paper studies the self-discharge behavior of double-layer supercapacitors with experimental and modeling methods. The movement of ions, side-reactions, and instability of the double layer are taken into consideration. The influence of various factors, such as the initial voltage, charge duration, short-term history, and current, on the self-discharge is simulated, showing good agreement with experimental data. The simulation of the ion distribution also gives a detailed explanation of the mechanism of self-discharge and verifies the interpretation of the relaxation process proposed in a recent study. It further clarifies the key role of the charging/discharging current in influencing charge redistribution during self-discharge, which was neglected in previous studies. The results show that the relaxation period during which the supercapacitor loses energy very quickly is due to the unbalanced distribution of ions, and it could be avoided by further charging or by applying a small charging current.