Effects of current collectors on the self-discharge rates of supercapacitors with aqueous electrolyte

Abstract

Current collectors play an important role in supercapacitors, impacting not only their electrochemical properties such as rate performance and cycling stability but also their self-discharge processes. In this study, we investigate the self-discharge behaviors of activated carbon supercapacitors with various current collectors, including titanium (Ti) foil, nickel (Ni) foil, 316 stainless steel (SS) foil, and graphite paper (GP), in an aqueous electrolyte. Our findings reveal that at a relatively low charging voltage of 0.8 V, supercapacitors with different current collectors exhibit similar decays in open circuit voltages (OCVs) after 12 h, indicating comparable self-discharge rates. However, at higher charging voltages, SS-based supercapacitors exhibit significantly faster self-discharge compared to Ti, Ni, and GP. Particularly at 1.6 V, the 12-h voltage retention rates decrease from over 60 % for Ti, Ni, and GP supercapacitors, to 46 % for SS supercapacitors. Analysis of the self-discharge mechanism suggests that increased side Faradaic reactions occurring at higher charging voltages in SS-based supercapacitors contribute to the accelerated self-discharge process compared to Ti, Ni, and GP supercapacitors.