Ultra high energy density and environmental friendly all graphene-Li+/K+ ion supercapacitors with double cation eutectic water in salt electrolyte

An all-graphene symmetric Li + /K + ion pseudocapacitor containing a double cation "water-in-salt" electrolyte with a very high capacity and energy density was designed and fabricated. Environmental considerations have been taken into account in the design of this scalable hybrid supercapacitor. A combination of reduced graphene oxide (RGO) and graphene oxide (GO) with mass ratio of 70:30 is used as an active electrode material pressed on the stainless steel mesh without using of a pollutant non-conductive organic binder. RGO/GO electrode material in contact with the ∼32 m CH 3 COO(Li 0.2 K 0.8 ).1.3H 2 O “water in salt” electrolyte showed very high charge storage capability (721.5 Fg −1 ) and excellent energy density of 530.1 W h kg −1 at the power density of 4148.8 W kg −1 , in the wide potential window of 2.3 V. The high capacity and energy density of this electrode is due to the high operating potential window of the employed aqueous electrolyte (2.3 V) and the utilizing three charge storage processes: 1) Formation of an extended electrochemical double layer (EDL) due to the use of graphene oxide and reduced graphene oxide with a high specific surface area, 2) Utilizing surface pseudocapacitive reactions by functional groups mainly located on the surface of graphene oxide and 3) Benefiting from the redox reaction of diffusing Li/K ions from the bulk electrolyte.