Synthesis of hierachical bio-inspired pine needle-shaped MnO2/CNTs/carbon cloth composite as highly cycling stable symmetrical supercapacitor

Abstract

In this work, bio-inspired hierarchical pine needle-shaped MnO<inf>2</inf>-CNTs-CFC composite was prepared by an environmentally-friendly two-step electrophoretic deposition (EPD) method. The synthesis of MnO<inf>2</inf> on CNTs was inspired by the "pine needle". The nanostructured needle-shaped MnO<inf>2</inf> which is more resistant than that larger MnO<inf>2</inf> structures to fracture, due to no sufficient initiate crack propagation for the total elastic energy stored in a small nanostructure during deformation, which would effectively enhance the cycling stability. The CNTs serve as substrate providing a conductive channel for MnO<inf>2</inf> to harvest and store the charge. The large quantity of CNTs on the surface of carbon cloth may facilitate the loading of Pine needle-shaped MnO<inf>2</inf>, providing high speed channels for the charge carrier and pseudocapacitance. The electrochemical results show specific capacitance of 381.74 F·g^-1, the energy density of 35.6 Wh·kg^-1 at a scan of 1 mV·s^-1 and capacitance retention ratio of 85% at a scan of 500 mV·s^-1. The capacitance retention ratios of the flexible MnO<inf>2</inf>-CNTs-CFC hybrid are no less than 75% when they endure various mechanical deformations. The flexible supercapacitor is obtained with promising electrochemical properties and rosy flexibility, demonstrating its great potential for wearable storage devices.