Rate-controlling element in the self-discharge process in electrochemical double-layer capacitors

Abstract

Suppression of self-discharge is crucial in the development of electrochemical double-layer capacitors (EDLCs). In this study, the rate-controlling element of the self-discharge process in EDLCs was explored without any new additives, and the anion was found to play a critical role in this process. The thickness ratio between the positive and negative electrodes (P/N ratio) was the primary factor used to control the self-discharge rate. As the P/N ratio increased, the anion density in the positive electrode decreased. The P/N ratio was increased to retain the anions for a longer period in the cell, which caused self-discharge suppression and led to a slow change in the positive electrode potential when held at an open-circuit status. Cells with a P/N ratio of 1.37 showed 26 to 32% reduced voltage decay than did those with a P/N ratio of 1.00 after 70 h.