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 alizarin red S, p-phenylenediamine redox electrolytes dissolved in the KOH solution is employed as the anodic electrolyte. 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 capacitance retention of 93.9% after 4000 charge/discharge cycles at 6 A g−1. It remains its high performance even under different bending conditions. Such high performance originates from improved solubility and stability of used redox electrolytes in alkaline media as well as their matched capacitive performance. This redox-electrolyte enhanced and flexible SC device offers a new method to ensemble power suppliers that can be integrated into modern wearable electronics and smart devices.