Abstract:

Having a substantial impact on the energy conversion efficiency of supercapacitors, self-discharge is an essential metric to consider when evaluating their performance. Understanding the self-discharge mechanism, creating realistic simulation models, and designing optimal procedures are all necessary for supercapacitors to be practical. However, many types of research were just concentrated on the improvement of other parameters, e.g., energy/power density and lifespan. Less attention has been paid to the self-discharge performance of supercapacitors. Consequently, the progress of supercapacitor self-discharge research in recent years is discussed in this work to support the growth of self-discharge research. The influencing factors and mathematic models for different self-discharge mechanisms (charge redistribution, activation control, diffusion control, and potential driving) are summarized in detail. Self-discharge limitation approaches using several tactics (charging proposal, surface-chemistry alteration, electrode coating, and functional electrolyte/separator) are also discussed. This paper emphasizes that the corresponding works should be performed in three aspects in the future: First, it is necessary to develop an accurate evaluation system of self-discharge according to various application requirements. Second, to build a reliable identification technique for distinct self-discharge processes and identify their origins, simulation approaches must be combined with modern characterization technologies. Finally, it is necessary to establish specific optimization methods according to the different self-discharge mechanisms to achieve the simultaneous optimization of self-discharge and other electrochemical performances.

Key words: supercapacitor, self-discharge, porous carbon, electric double-layer