An ultrahigh performance supercapacitors based on simultaneous redox in both electrode and electrolyte

A novel supercapacitor system with an ultrahigh electrochemical performance was prepared by applying a multi-walled carbon nanotubes (MWCNTs) - polyaniline (PANI) composite electrode and a redox potassium iodide (KI) electrolyte. The composite electrode possessed a good conductivity and a consecutive 3D conductive network. The amazing electrochemical performance came from the simultaneous redox reaction in both electrode and electrolyte. The maximum discharge specific capacitance was up to 4960 F/g (0.1 A/g) when the concentration of KI electrolyte was only 0.05 M in a three-electrode system. After 1000 charge-discharge cycles, it still reached to 1550 F/g when the current density was increased to 1.5 A/g. Furthermore, the specific capacitance, energy density and power density of 726 F/g, 100.8 Wh/kg and 499.8 W/kg, respectively, were also obtained in an asymmetric two-electrode system. •A supercapacitor with ultrahigh capacity was prepared.•A pair of redox electrode and electrolyte was used.•The capacity came from a synergetic redox effect.•The maximum discharge capacity is 4960 F/g.•The maximum energy density is 95.4 Wh/kg.