Construction and Electrochemical Properties of Solid‐state Supercapacitors with Redox Additives

Abstract Adding redox additives to conventional electrolytes is considered to be an effective method to improve electrochemical performance of the supercapacitors, which is ascribed to the additional Farady capacitance derived from the reversible redox reaction. Here, the influence of K3Fe(CN)6 on electrochemical properties for single electrode system and the assembled solid‐state supercapacitor are investigated. The carbon felt (CF) electrode in the mixed solution of K3Fe(CN)6/KCl exhibits remarkable specific capacitance of 2.45 F cm−2 after 5000 cycles, obviously much higher than conventional electrolyte KCl. The capacitance retention and the coulombic efficiency of the solid‐state supercapacitor maintains 86.5% and 97% after 2500 cycles, symmetric supercapacitor shows a high energy density of 58 mWh L−1 at power density of 660 mW L−1. Furthermore, the solid‐state SCs exhibit excellent flexibility and four supercapacitors are capable of lighting up an LED lamp, demonstrating the potential of practical applications of the as‐prepared solid‐state SCs.