3D self-supporting heterostructure NiCo-LDH/ZnO/CC electrode for flexible high-performance supercapacitor

Abstract

Two kinds of nanostructured ZnO, namely nanorods (ZnO NR) and nanoflakes (ZnO NF) were first prepared on conductive flexible carbon cloth (CC) by a hydrothermal route. Then nickel cobalt layered double hydroxide (NiCo-LDH) nanoflakes were directly hydrothermally deposited on them to construct three-dimensional (3D) self-supporting heterostructure NiCo-LDH/ZnO NR/CC and NiCo-LDH/ZnO NF/CC flexible electrodes. The effects of different nanostructured ZnO on morphology, structure and electrochemical performance of NiCo-LDH/ZnO/CC composite materials were investigated. It is found that NiCo-LDH nanoflakes grown on ZnO NF/CC substrate are more compact and uniform than those on ZnO NR/CC substrate. Moreover, NiCo-LDH/ZnO NF/CC electrode presents better electrochemical properties than NiCo-LDH/ZnO NR/CC electrode with 2.6 times higher specific capacitance (1577.6 F g−1 at 1 A g−1), 2.2 times better rate capability, and 1.5 time greater cycle stability, which may be attributed to the larger contact area and more redox-active sites provided by the NiCo-LDH NFs grown on ZnO NFs. Furthermore, the as-assembled solid-state flexible NiCo-LDH/ZnO NF//AC (active carbon) asymmetric supercapacitor (ASC) delivers a maximal energy density of 51.39 Wh kg−1 (800 W kg−1) with a high operating window of 1.6 V, and exhibits great cyclic stability with 87.3% capacitance retaining after 1000 cycles, which is higher than many reported ASCs. Finally, two packaged ASCs in series successfully lighted a red light-emitting diode (LED, 2.2 V/20 mA), evincing the potentiality of practical application.