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ORIGINAL PAPER

Ni-Co layered double hydroxide nanosheet array on nickel foam coated graphene for high-performance asymmetric supercapacitors Aiju Tang 1 & Peipei Chen 1 & Changhuan Mi 1 Received: 13 May 2020 / Revised: 8 July 2020 / Accepted: 2 August 2020 # Springer-Verlag GmbH Germany, part of Springer Nature 2020

Abstract Ni-Co layered double hydroxide (Ni-Co LDH) nanosheet is a promising electrode material for high-performance supercapacitors, but it has low specific capacity and poor rate performance due to its low conductivity. In this paper, a high specific surface area zeolite-based metal organic framework (MOF) dodecahedral cobalt-based nanomaterial (ZIF-67) was used as a cobalt source and a sacrificial template. The ZIF-67 template was etched by the hydrolysis of Ni2+ at room temperature; LDH materials are coprecipitated in solution. The material has a hierarchical structure of interdigitated nanosheet arrays, and the ordered nanosheet array facilitates effective contact of the active material with the electrolyte and rapid diffusion of ions. The conductive graphene is coated on the foamed nickel (rGO/NF) to form an excellent conductive structural support, thereby accelerating the transmission of electrons on the substrate. At a current density of 1 A g−1, the specific capacitance of Ni-Co LDH/rGO/NF is as high as 2505 F g−1. When the current density is increased to 20 A g−1, the capacity retention can reach 81%. An asymmetric capacitor was assembled by using Ni-Co LDH/rGO/NF as the positive electrode and biomass-derived nitrogen-doped porous carbon (QPC) as the negative electrode with an operating voltage range of 0–1.5 V. The Ni-Co LDH/rGO/NF//QPC asymmetric supercapacitor has an energy density of 76 Wh kg−1 at a power density of 747.5 W kg−1. When the power density reaches 7486.6 W kg−1, the energy density is still 35 Wh kg−1. Keywords ZIF-67 . Ni-Co layered double hydroxide . Grapheme . Performance . Asymmetric supercapacitor

Introduction With the development of social economy, the issue of environmental energy has become one of the key issues that cannot be ignored. The low, clean, and efficient energy storage materials are crucial. Layered double hydroxides (LDHs) have high specific capacitance, good redox reversibility, and environmental protection. They are often used in electrochemical energy storage materials and are used in capacitor materials [1–3]. The chemical formula of LDHs can be expressed as Electronic supplementary material The online version of this article (https://doi.org/10.1007/s11581-020-03729-9) contains supplementary material, which is available to authorized users. * Changhuan Mi [email protected] 1

College of Material Science and Technology, Jiangsu Key Laboratory of Electrochemical Energy Storage Technologies, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, People’s Republic of China

[M2+1−xM3+x(OH)2]x+·[An−x/n]x-·zH2O, M2+ and M3+ are generally divalent and trivalent metal ions, and An− is a layer of inorganic or organic cations, z is the number of