Self‐discharge in supercapacitors. Part I: Conway's diagnostics

Supercapacitors have emerged as drivers for the advancement of green energy technologies in energy storage systems and energy‐efficient devices. Their ability to rapidly acquire and deliver charge at high current densities and long cycle life is key. However, their high self‐discharge rates prevent their potential use in a wide range of applications, especially when utilizing commonly available activated carbon electrodes. Addressing this bottleneck is hindered by the lack of a comprehensive understanding of the self‐discharge processes. In this article, we provide a concise overview of various types of supercapacitors, followed by an exploration of self‐discharge phenomena within electrochemical systems. Recognizing the limited understanding at a molecular level, this article focuses on characterizing self‐discharge through the nature of the gradual decline in cell potential. We then survey the use of diagnostic methods in the literature to elucidate one or more controlling mechanisms operating during self‐discharge, facilitating a rational search for mitigation. We conclude by emphasizing the need for caution when interpreting controlling mechanisms solely based on cell potential measurements over time. This article is categorized under: Emerging Technologies > Energy Storage