Friction generated and Hele-Shaw cell designed facile alternative electrodes for high energy density supercapacitors

Abstract

Design of an electrode is an important aspect to enhance the energy density of an energy storage device. However, challenges with conventional brush-coated electrodes still exist in achieving the goal of stable electrochemical performances. Herein, for the first time, island-structured and fractal-like electrodes are made by the friction generated and lifted Hele-Shaw cell method, respectively, using few-layer graphene (FLG). The island-structured electrodes exhibit a large perimeter-to-area ratio of >1 μm−1 as compared to the fractal-like electrodes. The surface is more irregular, rough, and porous in the case of an island-structured electrodes resulting in a large fractal dimension (Df) of 2.83. The island-structured electrode shows nearly two-fold gravimetric capacitance (CS) of 145 F g−1 at 0.50 A g−1 for three-electrode test as compared to brush-coated (77.2 F g−1) under 0.5 M K2SO4 aqueous electrolyte. However, a symmetric device capacitance (Cdev) of 57.5 F g−1 at 0.50 A g−1 is found for full configuration test for island-structured electrodes. A 27 % enhanced energy density (E) of 5.1 Wh kg−1 at power density (P) of 800 W kg−1 is obtained for island-structured electrodes as compared to brush-coated. Also, charge-transfer resistance (R2) is low for the island-structured electrodes (3.6 Ω). A practical aqueous device with total Cdev of 8.1 F g−1 at 0.1 A g−1 is demonstrated with lighted LED using FLG as the electrode material. Under aqueous electrolyte conditions, the FLG device obtains an E of 4.5 Wh kg−1 at P of 100 W kg−1. Considering its large capacitance, easy fabrication, and short processing time, an island-structured electrode can be a better choice for energy storage devices.