Multishelled Nickel–Cobalt Oxide Hollow Microspheres with Optimized Compositions and Shell Porosity for High-Performance Pseudocapacitors

Abstract

Nickel-cobalt oxides/hydroxides have been considered as promising electrode materials for a high-performance supercapacitor. However, their energy density and cycle stability are still very poor at high current density. Moreover, there are few reports on the fabrication of mixed transition-metal oxides with multishelled hollow structures. Here, we demonstrate a new and flexible strategy for the preparation of hollow Ni-Co-O microspheres with optimized Ni/Co ratios, controlled shell porosity, shell numbers, and shell thickness. Owing to its high effective electrode area and electron transfer number (n(3/2) A), mesoporous shells, and fast electron/ion transfer, the triple-shelled Ni-Co1.5-O electrode exhibits an ultrahigh capacitance (1884 F/g at 3A/g) and rate capability (77.7%, 3-30A/g). Moreover, the assembled sandwiched Ni-Co1.5-O//RGO@Fe3O4 asymmetric supercapacitor (ACS) retains 79.4% of its initial capacitance after 10 000 cycles and shows a high energy density of 41.5 W h kg(-1) at 505 W kg(-1). Importantly, the ACS device delivers a high energy density of 22.8 W h kg(-1) even at 7600 W kg(-1), which is superior to most of the reported asymmetric capacitors. This study has provided a facile and general approach to fabricate Ni/Co mixed transition-metal oxides for energy storage.

Multishelled Transition Metal‐Based Microspheres: Synthesis and Applications for Batteries and Supercapacitors

“…Similarly, our group further fabricated mixed‐transition metal oxide multishelled structures by a one‐step synthesis and adsorption, such as nickel–cobalt oxide, Ni‐ and Co‐doped Fe 2 O 3 , and Ni–Co–O microspheres. With optimized Ni/Co ratios, a deeper penetration of metal cations can be realized. Additionally, using ethylene glycol instead of deionized water as the solvent could decrease the hydrophilia of the Ni 2+ /Co 2+ coordination sphere and increase its permeation into the RF microspheres ( Figure ).…”

“…Copyright 2017, Elsevier Science. f–i) Reproduced with permission . Copyright 2016, American Chemical Society.…”

“…Remarkably, the asymmetric supercapacitor manifested a high capacitance retention of 78.8% over 10 000 cycles. Furthermore, our group also reported the synthesis of multishelled hollow microspheres with mixed transition metal oxides, such as NiCo 2 O 4 , and nickel–cobalt oxide with optimized Ni/Co ratios, exhibiting excellent performance because of the tuned multishelled hollow structures with more electroactive sites and faster electrolyte permeation.…”

In Situ Synthesis and Electrophoretic Deposition of NiO/Ni Core-Shell Nanoparticles and Its Application as Pseudocapacitor

“…Thus, after a thermal treatment of 325 °C-60min, low loading densities and the increase of macroporosity results that the most of the NiO/Ni grains are active surfaces linked to the Ni foam. To quantify the electrolyte diffusion through the microstructural pathways, the diffusion coefficients (D) were calculated by the Randles-Sevcik Equation (12).…”

“…However, the consolidation of the electroactive material is not considered. The research works developed by Feng et al [10], Zhang et al [11] and Li et al [12] are mainly focused on the synthesis of nanostructures, and they do not consider the influence of the processing parameters in the final electrochemical behavior.…”