Engineering the Hierarchical Heterostructures of Zn-Ni-Co Nanoneedles Arrays@Co-Ni-LDH Nanosheets Core-Sheath Electrodes for Hybrid Asymmetric Supercapacitor with High Energy Density and Excellent Cyclic Stability

To meet the requirement for the high-ranked positive electrode materials having auspicious pseudocapacitive features for potential application in energy storage devices, the suitable designs of unique core–shell heterostructures featuring mixed transition metal oxide and layered double hydroxide (LDH) are highly needed and have been progressing expeditiously in recent years. Herein, 3D hierarchical zinc–nickel–cobalt (ZNCO)@Co–Ni-LDH (LDH-1 and LDH-2) core–shell nanostructured arrays on Ni foam as a pseudocapacitive electrode are prepared by using a facile hydrothermal and metal–organic framework (MOF) assisted coprecipitation method. FE-SEM images show that the core 1D ZNCO and shell 2D Co–Ni-LDH are well interconnected to form 3D porous and hierarchical ZNCO@Co–Ni-LDH core–shell nanostructures, leading to the fast and efficient transmission/transfer of both electrolyte ions and electrons, due to the higher electroactive surface areas and enhanced electrical conductivity. In a three-electrode system, the ZNCO@Co–Ni-LDH-2 electrode material delivers excellent electrochemical performance with higher specific capacitance of 2866 F g–1 at 1 A g–1 with ultrahigh capacitance retention of 68.35% at a higher current density of 10 A g–1 and excellent life span of 89% capacitance retention after 8000 cycles. Moreover, the sandwiched asymmetric supercapacitor (ASC) device using ZNCO@Co–Ni-LDH-2 as the positive electrode and N-doped graphene hydrogel (NGH) as the negative electrode exhibits superior specific capacitance (178 F g–1 at 1 A g–1), outstanding rate capability (70.22% at 10 A g–1), excellent life span (91.2% after 8000 cycles at 10 A g–1), and very high energy density (63.28 W h kg–1 at power density of 796.53 W kg–1).