Yarn-Shaped Hybrid Carbon Nanotube Supercapacitor with Enlarged Surface Area by ZnO Nanorod Forest Containing Pseudo-Capacitive Material

Recently, the fiber supercapacitor based on carbon nanotube (CNT) yarn has been reported in many literatures. CNT yarn has owned high-strength, high thermal-electrical conductivity, and flexibility. Zinc oxide nanorods (ZnO-NR) can provide an enlarged surface area, which can enhance an electrochemical performance. Nickel-cobalt layered double hydroxide (NiCo-LDH) is well known as pseudo-material with high theoretical capacitance, low-toxicity and diverse nanostructures. The NiCo-LDH coated ZnO-NR grown on CNT yarn electrode achieve maximum capacitance of 1051 mF cm^-2 (1261 F g^-1) at scan rate of 5 mV s^-1. It also shows excellent cycling stability with 60.5% capacitance retention after 7000 charge-discharge cycles at a current density of 75 mA cm^-2. Moreover, we also fabricate a flexible symmetric supercapacitor (NiCo-LDH/ZnO-NR/CNT// NiCo-LDH/ZnO-NR/CNT) with PVA–LiOH gel as separator and electrolyte. It can open large potential window up to 1.2 V. Furthermore, the device remains more than 90% capacitance after applying 150^o bending angle. Finally, we have successfully fabricated a flexible electrode based on NiCo-LDH/ZnO-NR/CNT yarn by a hydrothermal method that has the potential candidate for the flexible and high performance supercapacitor.