2, Kyung Hee University, Yongin-Si, Gyenggi-do, Korea (the Republic of)
Recently, supercapacitors (SCs) are emerging as one of the most representative power sources among the miscellaneous energy storage devices owing to their high power density, fast charge/discharge cycles and excellent cycling stability. Compared with the planar/rigid SCs, fiber-type SCs (FSCs) have fascinated much research attention to be used as a flexible power sources for the design innovation of reconfigurable and lightweight electronic products. Benefited from the yarn-shaped configuration, FSCs can be easily embroidered into human cloths, which open up a new avenue in the development of electronic textiles. However, apart from the merits of tiny size and high flexibility, FSCs still suffer from lower energy density compared with batteries due to their narrow potential window. To improve the energy density, fabrication of hybrid device configuration with transition metal oxides and carbonaceous materials is a strategic idea. Accordingly, research efforts have been focused on the fabrication of flexible hybrid FSCs (FHSCs). Together with incessant efforts to improve the energy density of FHSCs, the investigation of low-cost current collectors and novel nanostructured materials are also important, because the major contribution of fabrication cost is mainly based on both of these components. Besides, electronic waste (e-waste) is also considered as one of the fastest growing solid waste stream around the world in recent years. Waste from the discarded electronic modules and electric household appliances are commonly known as an e-waste. These are environmentally harmful on one side and precious on another side. Particularly, virtually useless electric cable wires (which have metallic fibers) can be often seen in large piles of leftover in storage rooms/dumping yards. Utilizing these e-waste cable wires to energy storage devices not only decreases the fabrication cost but also increases the economic value and decrease the reliance on fossil fuels. Inspiring from the recycling approach of old cable wires, herein we fabricated FHSCs using copper (Cu) fibers (peeled out from cable wires) and forest-like NiO nanosheets anchored carbon nanotubes coated CuO nanowires (NiO@CNTs@CuO NWAs) as an active material. The forest-like NiO@CNTs@CuO NWAs composite material was facilely prepared on braided Cu fibers by means of wet-chemical methods and used as an efficient positive electrode material. The fabricated solid-state FHSCs with forest-like composite material (positive electrode) and activated carbon coated carbon fibers (negative electrode) showed a high potential window of 1.55 V with excellent electrochemical properties including high energy density (26.32 Wh/kg) and power density (1218.33 W/kg), which can be able light up electronic devices effectively.