Layered double hydroxides (LDHs) have attracted broad
attention
as cathode materials for hybrid supercapacitors (HSCs) because of
their ultrahigh theoretical specific capacitance, high compositional
flexibility, and adjustable interlayer spacing. However, as reported,
specific capacitance of LDHs is still far below the theoretical value,
inspiring countless efforts to these ongoing challenges. Herein, a
hierarchical nanocage structure assembled by NiCo-LDH nanosheet arrays
was rationally designed and fabricated via a facile solvothermal method
assisted by the ZIF-67 template. The transformation from the ZIF-67
template to this hollow structure is achieved by a synergistic effect
involving the Kirkendall effect and the Ostwald ripening process.
The enlarged specific surface area co-occurred with broadened interlayer
spacing of LDH nanosheets by finely increasing the Ni concentration,
leading to synchronous improvement of electron/ion transfer kinetics.
The optimized NiCo-LDH-210 electrode displays a maximum specific capacitance
of 2203.6 F g–1 at 2 A g–1, excellent
rate capability, and satisfactory cycling stability because of the
highly exposed active sites and shortened ion transport paths provided
by vertically aligned LDH nanosheets together with the cavity. Furthermore,
the assembled HSC device achieves a superior energy density of 57.3
Wh kg–1 with prominent cycling stability. Impressively,
the design concept of complex construction derived from metal-organic
frameworks (MOF) derivatives shows tremendous potential for use in
energy storage systems.
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