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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).