A High-Performance Flexible Supercapacitor Using Dual Alkaline Redox Electrolytes

Abstract

Supercapacitors (SCs) feature high power densities and fast charging/discharging rates but suffer from low energy densities. The introduction of redox species into the electrolytes have been proposed as an effective approach to overcome this challenge. To further improve the energy density of such SCs, a mixture of two redox species of alizarin red S, p-phenylenediamine redox electrolytes dissolved in the KOH solution is employed as the anodic electrolyte in this work. Two flexible capacitor electrodes—holey reduced graphene oxide (hrGO) and Ni−Co hydroxide/oxide hydroxide nanosheets coated hrGO—are further prepared and utilized to ensemble a flexible asymmetric SC device with aid of gel polymer electrolytes. This flexible SC device possesses a cell voltage of 1.5 V, a maximum energy density of 40.8 Wh kg −1 with a power density of 750 W kg −1 , and 99.2% capacitance retention after 5000 charge/discharge cycles. It remains its high performance even under different folding conditions. Such high performance originates from improved solubility and stability of used redox electrolytes in alkaline media and their matched performance with that of the cathode. This flexible SC device offers a new strategy to ensemble power suppliers that can be integrated into modern wearable electronics and smart devices.