Flexible High-Energy-Density 4.3 V Supercapacitor Based on a Trimetallic Sulfide Cathode and a Bimetallic Sulfide-Polypyrrole Anode with an Ionic Liquid Gel Polymer Electrolyte

Abstract

Battery-type electrode materials have recently been explored as an exclusive class of high-capacity cathode materials for the advancement of hybrid supercapacitors. The electrode materials’ higher specific energy, long-term cycle stability, and faster ion transportation are commendable attributes that have prompted researchers to envisage high-performance cathode materials. The hierarchically structured electrodes provide optimal redox sites and channels for accelerating the transit of ions and electrons between the electrodes and electrolytes. Electropolymerization and a facile hydrothermal procedure followed by calcination were used to concoct Cu–Fe–Co-based trimetallic sulfide and Ni–Fe-based bimetallic sulfide with the polypyrrole composite over carbon cloth for the development of a flexible asymmetric supercapacitor. The hierarchical core–shell Cu4Fe2Co2S4 hybrid composite on carbon cloth was used as a high-performance cathode material for solid-state supercapacitors. The Cu4Fe2Co2S4 electrode exhibits a capacitance retention of 84.87% after 10,000 cycles and a specific capacitance of 334 mAh/g at 4 mA/cm2. In addition, the electropolymerized Ni2FeS4-Ppy on carbon cloth was initially reported as the recent anode, with a retention of the capacitance of 92.32% after 10,000 cycles, a specific capacitance of 1228 mAh/g at 8 mA/cm2, and a significantly increased specific energy of 790 Wh/kg. The ionic liquid polymer-based electrolyte gel assembled flexible all-solid-state asymmetric supercapacitor Ni2FeS4-Ppy/PVA-DMSO-EMIM-BF4/Cu4Fe2Co2S4 has a specific energy of 756.7 Wh/kg and specific power of 10750 W/kg, indicating a specific capacity of 352 mAh/g and remarkable retention of the capacitance of 96% after 10,000 cycles. These unrivaled inorganic–organic amalgamation systems strengthen the synergistic development of innovative functional electrode materials for energy storage applications with improved cyclic stability and rate capability.