Fluorinated Ether‐Based Electrolyte for Supercapacitors with Increased Working Voltage and Suppressed Self‐discharge

Abstract The application of supercapacitors for long‐term energy storage is largely limited by their low energy density and self‐discharge behavior. Finding a way to effectively increase the voltage window (and thus the energy density) and suppress the self‐discharge of supercapacitors is a huge research challenge. Herein, by introducing a fluorinated ether, 1,1,2,2‐tetrafluoroethyl‐2,2,3,3‐tetrafluoropropyl ether (TTE), in triethyl ammonium tetrafluoroborate/acetonitrile solution as the electrolyte of supercapacitors, improved electrolyte stability could be achieved. As a result, a working voltage of 3.6 V was obtained, much higher than the typical working voltage of 2.7 V for acetonitrile‐based electrolytes without TTE. In addition, reduced self‐discharge was attained after adding TTE in the electrolyte. When charged to 3.6 V, the supercapacitors using TTE‐based electrolyte exhibited an open circuit voltage (OCV) decay of 2.03 V after 24 h, lower than that of the supercapacitors without TTE (2.60 V). Mechanistic analysis indicated that the slower self‐discharge could be attributed to the suppressed activation‐controlled faradaic reaction process caused by electrolyte decomposition.