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

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.