Superconcentrated aqueous electrolyte to enhance energy density for advanced supercapacitors

We here report a superconcentrated potassium acetate (KAC) solution (75[Formula: see text]wt.%, K : H 2 O [Formula: see text] 1 : 1.8, called as “water-in-salt”) as an aqueous electrolyte to improve the working voltage and increasing capacitance in enhancing the energy density of the active carbon-based aqueous supercapacitor. The stability potential window of the superconcentrated electrolyte realizes an AC//AC symmetric supercapacitor with operating voltage of 2.0 V and excellent cyclic performance. Meanwhile, the energy density of such supercapacitor achieves about twice as high as that of the supercapacitor using normal concentration of electrolyte.