Flexible Solid-State Asymmetric Supercapacitor with High Energy Density and Ultralong Lifetime Based on Hierarchical 3D Electrode Design

Abstract

Hierarchical structure design of transition metal compounds is a promising method for improving the electrochemical properties of supercapacitors. In this work, a 3D electrode is obtained by in situ growing of NiMoO4@NiCo2O4 core–shell nanorods on Ni foam (NF) followed by an annealing process (NF@NiMoO4@NiCo2O4). The hierarchical structure with ordered pores on a surface enables a uniform charge distribution, provides effective electron/ion transfer channels, and maintains structural integrity over long periods of cycling, which collectively results in excellent electrochemical properties with an extraordinary specific capacitance of 1920 F g–1 at 1 A g–1 as well as 91.6% capacitance retention after 10 000 cycles. Furthermore, a flexible solid-state asymmetric supercapacitor fabricated with NF@NiMoO4@NiCo2O4 achieves a superior energy density of 54.5 Wh kg–1 (at 845 W kg–1) and an outstanding cycling stability with 83% capacity retention over 10 000 cycles. The hierarchical 3D electrode design in this work will contribute to the development of high-performance supercapacitors and shows promising prospects in flexible and portable energy storage systems.

Construction of 3D Porous Carbon Frameworks for Supercapacitors: Abundant Pore Structure and Proper Hydrophilicity

“…The enlarged layer spacing and increased disorder may be attributed to the increased pore structure after adding KOH. 33 Thus, KOH-assisted activation confers more abundant pores and defects to the material. The degree of graphitization and disorder were further probed using Raman spectroscopy (Figure 3b).…”

“…The (002) peak shifted to a lower degree for the 3DPC samples, corresponding to a higher d (002) value, calculated by applying Bragg’s equation. The enlarged layer spacing and increased disorder may be attributed to the increased pore structure after adding KOH . Thus, KOH-assisted activation confers more abundant pores and defects to the material.…”

Electrostructural Compatibility of Battery-Type Diffuse-Porous Co9S8–NiCo2S4/Defective Reduced Graphene Oxide and Flaky FeS/Nitrogen-Doped Defective Reduced Graphene Oxide for Ultra-High-Performance All-Solid-State Hybrid Pseudocapacitors

“…The potentials of the multiple oxidation reactions overlap, and similarly, the potentials of the multiple reduction reactions overlap, which consequentially give rise to a pair of redox peaks in the CV profiles at various potential scan rates. 1 The shapes of the CV curves at various potential scan rates remain nearly unchanged, but the oxidation and reduction peaks shift respectively toward higher and lower potentials with an increase in scan rates. This is a fundamental physiognomy of porous electrode materials, which occurs due to the fact that a higher overpotential is required as the electrolyte ions experience increased steric hindrance while accessing the bulk electroactive surface of porous Co 9 S 8 −NiCo 2 S 4 /D-rGO at elevated scan rate/elevated reaction rate conditions.…”

“…In this context, supercapacitors (an effective connection between capacitors and batteries) are found to be one of the most advanced electrochemical energy storage systems, due to their high power/energy density output, supreme rate charge/discharge efficiency, and ultralong cyclability. 1,2 Therefore, supercapacitors are lately playing vital roles in hybrid electric transportation, portable high-performance devices, and large-scale backup systems. 3,4 Among various supercapacitors, redox capacitors/pseudocapacitors, based on battery-type electrode materials, possess significantly more charge storage capacity and rate efficiency than typical electrical double layer capacitors (EDLCs).…”

Facile Synthesis of NiCo2O4 Nanowire Arrays/Few-Layered Ti3C2-MXene Composite as Binder-Free Electrode for High-Performance Supercapacitors

“…Moreover, the nanostructured NiCo 2 O 4 is conducive to providing large specific surface area, higher storage site utilization and short ion diffusion path. However, the low electronic conductivity and serious agglomeration hinder its electrochemical performance [ 23 ]. A popular approach to avoid the limitation is to develop effective synthetic strategies and design composite materials by combining them with other high conductivity materials.…”