Engineering the Hierarchical Heterostructures of Zn-Ni-Co Nanoneedles Arrays@Co-Ni-LDH Nanosheets Core-Sheath Electrodes for a 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).