We propose a new concept of using a redox additive potassium ferrocyanide in 1-butyl-1-methylpyrrolidinium dicyanamide ionic liquid electrolyte for high-performance supercapacitors. Coupling with a unique nanostructure of N-doped reduced graphene oxide, the supercapacitor using this new hybrid electrolyte exhibits the excellent specific energy and power of 89 Wh kg^-1 and 3677 W kg^-1, respectively. An excellent long-term stability is demonstrated up to 10000 cycles of charge-discharge with 87% capacitance retention.