2.5 V High‐Performance Aqueous and Semi‐Solid‐State Symmetric Supercapacitors Enabled by 3 m Sulfolane‐Saturated Aqueous Electrolytes

Aqueous electrolytes show the potential of application for high‐performance supercapacitors. However, their limited operating voltages set limits for widespread applications. Herein, the feasibility of applying the sulfolane (SL)‐saturated 3 m LiTFSI aqueous electrolytes for supercapacitors is shown. These electrolytes possess high conductivities and wide electrochemical stable windows (ESWs), demonstrating the potential applications in high‐voltage supercapacitors. Activated carbon//3 m LiTFSI SL/Water //activated carbon supercapacitor is assembled to possess a high voltage of 2.5 V and outstanding capacitive performance (106 F g −1 at 0.5 A g −1 , >10 000 cycles). Also, a high areal capacitance up to 1.52 F cm −2 is obtained by applying a high mass loading electrode (13.06 mg cm −2 ). Furthermore, a flexible symmetric semi‐solid‐state supercapacitor (2.5 V) is fabricated. Impressive performance can be obtained. Thus, the finding suggests a promising electrolyte design for high‐voltage aqueous supercapacitors.