Freestanding Three-Dimensional Graphene/MnO₂ Composite Networks As Ultralight and Flexible Supercapacitor Electrodes

Abstract

A lightweight, flexible, and highly efficient energy management strategy is needed for flexible energy-storage devices to meet a rapidly growing demand. Graphene-based flexible supercapacitors are one of the most promising candidates because of their intriguing features. In this report, we describe the use of freestanding, lightweight (0.75 mg/cm(2)), ultrathin (<200 μm), highly conductive (55 S/cm), and flexible three-dimensional (3D) graphene networks, loaded with MnO(2) by electrodeposition, as the electrodes of a flexible supercapacitor. It was found that the 3D graphene networks showed an ideal supporter for active materials and permitted a large MnO(2) mass loading of 9.8 mg/cm(2) (~92.9% of the mass of the entire electrode), leading to a high area capacitance of 1.42 F/cm(2) at a scan rate of 2 mV/s. With a view to practical applications, we have further optimized the MnO(2) content with respect to the entire electrode and achieved a maximum specific capacitance of 130 F/g. In addition, we have also explored the excellent electrochemical performance of a symmetrical supercapacitor (of weight less than 10 mg and thickness ~0.8 mm) consisting of a sandwich structure of two pieces of 3D graphene/MnO(2) composite network separated by a membrane and encapsulated in polyethylene terephthalate (PET) membranes. This research might provide a method for flexible, lightweight, high-performance, low-cost, and environmentally friendly materials used in energy conversion and storage systems for the effective use of renewable energy.

Two-dimensional NiCo2O4nanosheet-coated three-dimensional graphene networks for high-rate, long-cycle-life supercapacitors

“…46 Lastly, the strong coupling between NiCo 2 O 4 NS and 3DGN renders good mechanical adhesion and electrical connection, avoiding the use of polymer binders and conductive additives and leading to enhanced electrochemical kinetics, which is good for high-rate capability and long-term cycling performance of supercapacitors. 12,22,27 In summary, we have successfully fabricated high-capacitance, high-rate, and long-cycle-life supercapacitors by synthesis of thin 2D NiCo 2 O 4 NS with a thickness of ∼6.4 nm on 3DGN. The novel NiCo 2 O 4 NS/3DGN hybrid demonstrates excellent electrochemical performances including ultrahigh specific capacitances as well as excellent rate capability of 2173 and 954 F g −1 at high current densities of 6 and 200 A g −1 , respectively, and superior long-term cycling stability with only 6% capacitance loss after 14 000 cycles at 100 A g −1 , which is obviously superior to most of the previously reported pseudocapacitor electrodes (Table S1 in ESI †).…”

“…Although high-capacitance pseudocapacitors have been achieved using pseudocapacitive materials as electrodes, they normally suffer from low power density and unstable cycling performance because of their intrinsically low electrical conductivity. [20][21][22] Due to their high porosity, large internal surface area, and outstanding electrical and mechanical properties, 23,24 three-dimensional graphene networks (3DGNs) serve as a striking platform for construction of composite electrodes with enhanced properties for wide applications, such as supercapacitors, 20,[24][25][26][27][28] Li-ion batteries, [29][30][31][32] catalysis, [33][34][35] and sensors. 26,36 Particularly, supercapacitors constructed from 3DGN based-materials have been studied to achieve enhanced electrochemical performances including higher specific capacitance, better rate capability and longer cycle life.…”

电化学离子交换法辅助制备可用作高性能超级电容器电极的Co3O4/NiCo2O4纳米复合材料

“…Even at a high discharge current of 150 mA cm -2 , the energy density can still remain 1.5 mW h cm −3 at a power density of 1.4 W cm -3 , which is higher than those of the recently reported devices and the details are shown in Fig. 6e [10,15,18,[49][50][51][52][53]. Fig.…”

Hierarchical mesoporous Co3O4@ZnCo2O4 hybrid nanowire arrays supported on Ni foam for high-performance asymmetric supercapacitors

“…The slope of the curves represents the Warburg impedance (W) in low frequency area, which shows the electrolyte diffusion in the electrode and proton diffusion in active materials. The Co 3 O 4 @ZnCo 2 O 4 hybrid NWAs electrode shows a larger slope than Co 3 O 4 NWAs electrode, implying the more excellent capacitive characteristics and the lower ion diffusion resistance [41,[43][44]. The equivalent circuit diagram is shown in the inset of Fig.…”