NiCo2O4/RGO Hybrid Nanostructures on Surface-Modified Ni Core for Flexible Wire-Shaped Supercapacitor

Abstract

In this work, we report surface-modified nickel (Ni) wire/NiCo2O4/reduced graphene oxide (Ni/NCO/RGO) electrodes fabricated by a combination of facile solvothermal and hydrothermal deposition methods for wire-shaped supercapacitor application. The effect of Ni wire etching on the microstructural, surface morphological and electrochemical properties of Ni/NCO/RGO electrodes was investigated in detail. On account of the improved hybrid nanostructure and the synergistic effect between spinel-NiCo2O4 hollow microspheres and RGO nanoflakes, the electrode obtained from Ni wire etched for 10 min, i.e., Ni10/NCO/RGO exhibits the lowest initial equivalent resistance (1.68 Ω), and displays a good rate capability with a volumetric capacitance (2.64 F/cm3) and areal capacitance (25.3 mF/cm2). Additionally, the volumetric specific capacitance calculated by considering only active material volume was found to be as high as 253 F/cm3. It is revealed that the diffusion-controlled process related to faradaic volume processes (battery type) contributed significantly to the surface-controlled process of the Ni10/NCO/RGO electrode compared to other electrodes that led to the optimum electrochemical performance. Furthermore, the wire-shaped supercapacitor (WSC) was fabricated by assembling two optimum electrodes in-twisted structure with gel electrolyte and the device exhibited 10 μWh/cm3 (54 mWh/kg) energy density and 4.95 mW/cm3 (27 W/kg) power density at 200 μA. Finally, the repeatability, flexibility, and scalability of WSCs were successfully demonstrated at various device lengths and bending angles.

Recent Advances and Challenges Toward Application of Fibers and Textiles in Integrated Photovoltaic Energy Storage Devices

“…Flexible Wires/Flexible Metal Matric/Metallic Fabrics Metal wires or metallic fabrics or meshes are extensively used as flexible current collector for SCs due to their excellent mechanical strength and high electrical conductivity [ 95 ]. For this purpose, various metal-based substrates have been explored including stainless steel (SS) [ 96 ], copper (Cu) wire [ 97 ], nickel (Ni) [ 95 ], and titanium (Ti) wire [ 98 ], which provide easy fabrication of electrode, high mechanical strength, and excellent conductivity. In addition to flexibility, the active materials deposited on these substrates during electrodes fabrication results in enhanced specific capacitance, energy, and power density, respectively.…”

Role of Carbon Nanotube for Flexible Supercapacitor Application

“…The two important terms such as energy and power densities are the very critical terms, which determine the performance of the SC devices. Figure 10c shows the energy and power densities of the fabricated devices as compared to the other reported literature [100][101][102][103][104].…”

Flexible supercapacitors toward wearable energy storage devices

“…Huang et al twisted a bale of thin stainless‐steel fibers into a yarn, which was utilized as a fibrous structural support (Figure 4). 27 This fiber supercapacitor utilizes highly conductive metallic fibers (wires and yarns) to avoid coating precious metals like Au on the plastic fiber 28 . Reduced graphene oxide (RGO), MnO 2, and PPy were deposited layer‐by‐layer over the yarn to get an RGO/MnO 2 /PPy composite material coated on the yarn electrode.…”

“…27 This fiber supercapacitor utilizes highly conductive metallic fibers (wires and yarns) to avoid coating precious metals like Au on the plastic fiber. 28 Reduced graphene oxide (RGO), MnO 2, and PPy were deposited layer-by-layer over the yarn to get an RGO/MnO 2 /PPy composite material coated on the yarn electrode. First, RGO was coated over the yarn by hydrothermal treatment.…”