A high performance asymmetric supercapacitor based on in situ prepared CuCoO nanowires and PPy nanoparticles on a two-ply carbon nanotube yarn.

One-dimensional supercapacitors (SCs) are of great interest for future wearable electronics, but improvement in both high capacitance and high flexibility is still a challenge. Herein, we fabricate a high performance yarn asymmetric SC (ASC) using in situ prepared CuCoO nanowires and polypyrrole (PPy) nanoparticles on the surface of a two-ply carbon nanotube (CNT) yarn. The parallel-shaped yarn ASC not only shows outstanding redox pseudocapacitance, including a high areal capacitance (59.55 mF cm), specific energy density (20 μW h cm) and power density (5.115 mW cm), but also exhibits good flexibility because of its well maintained capacitance during repeated dynamic bending states. The capacitance retention still remains 80.1% under 8000 cycles, suggesting relatively good reversibility and stability.