Diagnostic Identification of Self-Discharge Mechanisms for Carbon-Based Supercapacitors with High Energy Density

Charged supercapacitors are in a state of high free energy relative to that of the discharged state, so there is a internal drive-force for their self-discharge. The self-discharge behavior of supercapacitors is an important factor when considering the capability of charge hold and evaluation of performance. Several mechanisms of self-discharge are distinguished and measurements of the self-discharge rates of carbon-based tractive supercapacitors with nominal capacitance 50000F were presented. A hybrid mechanism of self-discharge which was combined ions diffusion mechanism with charge leakage was proposed, and predicted the dividing point between quick-down range and slow-down range of self-discharge curve with voltage and time. At initial stage, self-discharge process was led by ions diffusion mechanism within about 550 minutes, then the rest process was led by exponential function with amendment of diffusion mechanism.