Abstract
We report the synthesis of three dimensional (3D) NiCo2O4@NiCo2O4 nanocactus arrays grown directly on a Ni current collector using a facile solution method followed by electrodeposition. They possess a unique 3D hierarchical core-shell structure with large surface area and dual-functionalities that can serve as electrodes for both supercapacitors (SCs) and lithium-ion batteries (LIBs). As the SC electrode, they deliver a remarkable specific capacitance of 1264 F g−1 at a current density of 2 A g−1 and ~93.4% of capacitance retention after 5000 cycles at 2 A g−1. When used as the anode for LIBs, a high reversible capacity of 925 mA h g−1 is achieved at a rate of 120 mA g−1 with excellent cyclic stability and rate capability. The ameliorating features of the NiCo2O4 core/shell structure grown directly on highly conductive Ni foam, such as hierarchical mesopores, numerous hairy needles and a large surface area, are responsible for the fast electron/ion transfer and large active sites which commonly contribute to the excellent electrochemical performance of both the SC and LIB electrodes.
Highlights
On carbon nanofibers, presenting excellent specific capacitances of 905 and 888.7 F g−1, respectively, at 2 A g−1
NiCo2O4@NiCo2O4 nanocactus arrays (NCAs) core/shell structures were obtained through the growth of NiCo2O4 shell via an electrochemical deposition process
The Rct increased by 0.6 Ω after 5000 cycles confirming that the NiCo2O4@NiCo2O4 NCA nanostructures were well preserved, consistent with the very stable cyclic performance (Fig. 7b). These results demonstrated that the combination of fast ion diffusion and low electron transfer resistance resulted in enhanced electrochemical performance of the core/shell structured NCA electrode
Summary
On carbon nanofibers, presenting excellent specific capacitances of 905 and 888.7 F g−1, respectively, at 2 A g−1. Large volume changes and stresses commonly occur during the lithium insertion-exaction processes, resulting in pulverization of the electrodes and aggregation of electrode materials. This causes a large increase in contact resistance and significant capacity fade during cycling, limiting the commercial applications of these anode materials[11,12]. To satisfy the requirements of high specific capacitance, high specific capacity and durable structural stability, and to promote full utilization of the active materials for both SCs and LIBs, promising strategies include rational design of nano-architectured electrodes and hybridization of bespoke pseudocapacitive oxides. Freestanding electrodes are prepared without adding conductive additives or polymer binders due to the presence of the highly conductive rigid Ni foam substrate, substantially reducing the “dead volume” in electrode materials[21,22]
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