High-Energy-Density Asymmetric Supercapacitor Based on Layered-Double-Hydroxide-Derived CoNi_2S_4 and Eco-friendly Biomass-Derived Activated Carbon

摘要

Current work presents a high-performance asymmetric supercapacitor (ASC) using nanostructured cobalt nickel sulfide (CoNi_2S_4) derived via African marigold flower-like layered double hydroxide (CoNi-LDH) as a cathode and Manihot esculenta-derived activated carbon (MAC) synthesized from oxygen-rich hydrochar as an anode. Optimization for LDH precursors with different times of synthesis was carried out, and best performed CoNi-LDH-12 displayed a specific capacitance of 928 F/g at 1 A/g in a three-electrode system, which was further sulfurized with two different sulfur ratios to obtain CoNi_2S_4. As-prepared spinel CoNi_2S_4-800 achieved a remarkable specific capacitance of 1637 F/g at 2 A/g, and the specific capacity was found to be 184 mAh/g, whereas the capacitance for synthesized MAC was found to be 315 F/g at 0.5 A/g in a three-electrode system. The ASC device CoNi_2S_4/MAC fabricated offered remarkable energy densities of 55.37 and 10.66 Wh/kg at power densities of 3200 W/kg and 10.66 kW/kg, respectively. The prolonged cycle life studies of the ASC device for 5000 cycles achieved a coulombic efficiency of 95.90 with a capacitance retention of ～90.03, proving the electrode materials to be promising for energy storage application.