Rationally designed ultrathin Ni-Al layered double hydroxide and graphene heterostructure for high-performance asymmetric supercapacitor

A novel 3 dimensional (3D) heterostructure that is composed of exfoliated Ni-Al layered double hydroxide nanosheet and reduced graphene oxide (Ni-Al LDH/rGO) is synthesized by adopting a simple and feasible solution-phase technique. The unique hierarchical heterostructure has a stable layered structure, more active sites and fast electron transport channels, which play an important role for improving the cycle stability and rate capacity performance. The prepared Ni-Al LDH/rGO electrode exhibits excellent performance with a capacitance of 629.8 C g(-1) at 1 A g(-1), and a high specific capacitance of 471.6 C g(-1) even at a high current density of 20 A g(-1). The asymmetric supercapacitor (ASC) fabricated by using the Ni-Al LDH/rGO as the positive electrode and using active carbon (AC) as the negative electrode, which exhibits a high energy density of 58.6 Wh kg(-1) at the power density of 359 W kg(-1) and remains good cycle stability. The superior electrochemical properties are due to the 3D heterostructure, where the large specific surface area of rGO nanosheets serve as a conductive 2D backbone successfully offset structure limitation by the potential synergistic effect. The exfoliated ultrathin Ni-Al LDH nanosheets with only a few atomic layers in this architecture are expected to provide large reactive active sites for fast charge transfer. Therefore, the unique 3D heterostructure is favorable for stabilizing crystal structure and enhancing capability and cycling stability for pseudocapacitors during the charge-discharge process. (C) 2018 Elsevier B.V. All rights reserved.