Binder-free combination of large area reduced graphene oxide nanosheets with Cu foil for lithium ion battery anode

Binder-free combination of large area reduced graphene oxide (RGO) nanosheets with Cu foil was designed and achieved via one-step facile electro-reduction reaction. The obtained composite RGO/Cu foil electrode were studied in terms of scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), selected area electron diffraction (SAED), Raman, galvanostatic charge/discharge, AC impedance and cyclic voltammetry (CV). As expected, large area RGO nanosheets with micron order of magnitude successfully formed and tightly combined with Cu foil without any additional polymer binders. Furthermore, RGO/Cu foil electrode delivered a reversible discharge capacity of 870.3 mAh/g after 110 cycles, indicating satisfactory cyclic stability and rate performance. High Li-storage activity, eminent conductivity and tight binder-free integration of RGO nanosheets with Cu foil current collector should be responsible for high electrochemical performances.     

Preparation and electrochemical investigation of the polyaniline/activated carbon nanocomposite for supercapacitor applications

The polyaniline (PANI)/activated carbon (AC) nanocomposite electrodes were prepared by electropolymerization of aniline monomers on the surface of AC/polyvinyl alcohol (PVA) electrodes for supercapacitor studies. Fourier transforms infrared spectroscopy (FT-IR), X-ray diffraction (XRD), and scanning electron microscopy (SEM) analyses were performed to characterize the structure and morphology of the nanocomposite electrodes. The electrochemical properties of the prepared nanocomposite electrodes and the supercapacitive behavior of the PANI, AC, and AC/PANI/PVA electrodes were investigated using cyclic voltammetry (CV) and galvanostatic charge/discharge measurements, respectively. Morphological studies showed that a thin film of PANI has been uniformly deposited on the porous surface of AC electrode, and an ordered arrangement of nanostructures with interlinked porous network has been made. Electrochemical measurements showed that AC particles prevent the degradation of PANI chains during charge/discharge cycles. The specific capacitance of the AC/PANI/PVA nanocomposite electrode was 338.15 F/g which is higher than that of the pristine AC electrode (0.08 F/g). This is due to the contribution of PANI chains by their pseudocapacitance (redox reaction) properties. Although the specific capacitance of PANI electrode (378.57 F/g) was greater than that of the nanocomposite electrode, the cyclic stability of the PANI electrode was lower than that of the AC/PANI/PVA nanocomposite electrode.     

High dispersion of γ-MnO2 on well-aligned carbon nanotube arrays and its application in supercapacitors

The well-aligned carbon nanotube arrays (ACNTs) were used as supporting material and the γ-MnO₂/ACNT electrode with high dispersion of γ-MnO₂ has been prepared by electrochemically induced deposition method. The crystal structure and morphology of the γ-MnO₂/ACNT electrode were investigated by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The capacitive properties of γ-MnO₂/ACNT electrode were characterized by cyclic voltammetry and galvanostatic charge–discharge method. The specific capacitance of the γ-MnO₂/ACNT electrode is as high as 784 F g^− 1 based on γ-MnO₂ and 234 F g^− 1 based on γ-MnO₂/ACNT composites in 0.1 M Na₂SO₄ aqueous solution from 0 to 1 V when the charge–discharge current density is 1 mA cm^− 2. Additionally, the electrode shows excellent power characteristics, high electrochemical reversibility and excellent long-term charge–discharge cycle stability.     

Sulfur-incorporated,porous graphene films for high performance flexible electrochemical capacitors

Graphene and its derivatives are considered potential electrode materials for flexible electrochemical capacitors (f-ECs), but their capacitive performances have to be improved for practical applications. Herein, we demonstrate fabrication of flexible sulfur (S)-incorporated reduced graphene oxide (SRGO) electrodes obtained by pyrolyzing free-standing film consisting of benzyl disulfide-functionalized graphene oxides at 900 °C. The effect of S incorporation on morphology and chemical structure of SRGO were investigated by various microscopic and spectroscopic methods. Incorporation of S and the crumpled and porous morphology of SRGO electrodes improve capacitive performance of f-ECs; SRGO f-ECs show a specific capacitance of 140.8 F/g at 1 A/g, rate capability of 91.5% retention, and cyclic performance of 93.4% after 1000 charge/discharge cycles at 4 A/g. Impressively, SRGO f-ECs exhibit excellent electrochemical and mechanical durability after 1000 charge/discharge cycles at a bending angle of 120° with values that greatly exceed those of conventional RGO-based f-ECs. This study provides a fundamental foundation of the correlation between S composition of carbon nanomaterials and their electrochemical (or surface) properties.     

MoO3/reduced graphene oxide composites as anode material for sodium ion batteries

MoO₃/reduced graphene oxide (MoO₃/RGO) composites were successfully prepared via a facile one-step hydrothermal method, and evaluated as anode materials for sodium ion batteries (SIBs). The crystal structures, morphologies and electrochemical properties of the as-prepared samples were characterized by X-ray diffraction, field-emission scanning electron microscopy, cyclic voltammetry, electrochemical impedance spectroscopy, and galvanostatic charge/discharge tests, respectively. The results show that the introduction of RGO can enhance the electrochemical performances of MoO₃/RGO composites. MoO₃/RGO composite with 6 wt% RGO delivers the highest reversible capacity of ~208 mA h g⁻¹ at 50 mA g⁻¹ after 50 cycles with good cycling stability and excellent rate performance for SIBs. The excellent sodium storage performance of MoO₃/RGO should be attributed to the synergistic effect between MoO₃ and RGO, which offers the increased electrical conductivity, the facilitated electron transfer ability and the buffering of volume expansion.     

Kilohertz ultrafast electrochemical supercapacitors based on perpendicularly-oriented graphene grown inside of nickel foam

Ultrafast electrochemical supercapacitors (EC) that can work at or above kilohertz (kHz) frequency, 3–4 orders higher than traditional EC, call for a structure with extremely low equivalent serial resistance (ESR) and a reasonably large surface area. Three-dimensional perpendicularly-oriented graphene (POG) network, grown inside of Ni foam (NF) by microwave plasma chemical vapor deposition, is reported as electrode to fabricate such ultrafast EC. The folded POG inside NF provides a large surface area, while the straight-forward and wide-open porous structure of POG ensures fast ion migration. In conjunction with the intrinsic high electronic conductivity of graphene and Ni, POG/NF electrode based ultrafast EC was demonstrated with a specific cell capacitance of 0.32 mF/cm² at 1 kHz, a relaxation time constant of 0.248 ms, and an ESR of 70 mΩ. A charge–discharge rate as high as 500 V/s was also measured, at which the cyclic voltammogram maintained a rectangular shape, corresponding to a single electrode capacitance of 0.83 mF/cm².     

A hierarchical carbon fiber/sulfur composite as cathode material for Li–S batteries

A novel hierarchical structure carbon/sulfur composite is presented based on carbon fiber matrices, which are synthesized by electrospinning. The fibers are constituted with hollow graphitized carbon spheres formed using catalytic Ni nano-particles as hard templates. Sulfur is loaded to the carbon substrates via thermal vaporization. The structure and composition of the hierarchical carbon fiber/S composite are characterized with X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, and nitrogen adsorption isotherms. The electrochemical performance is evaluated by cyclic voltammetry and galvanostatic charge–discharge. The results exhibit an initial discharge capacity of 845 mA h g⁻¹ at 0.25 C (420 mA g⁻¹), with a retention of 77% after 100 cycles. A discharge capacity of 533 mA h g⁻¹ is still attainable when the rate is up to 1.0 C. The good cycling performance and rate capability are contributed to the uniform dispersion of sulfur, the conductive network of carbon fibers and hollow graphitized carbon spheres.     

Improved activity of a graphene–TiO2 hybrid electrode in an electrochemical supercapacitor

We present a simple and fast approach for the synthesis of a graphene–TiO₂ hybrid nanostructure using a microwave-assisted technique. The microstructure, composition, and morphology were characterized by X-ray diffraction, Fourier-transform infrared spectroscopy, Raman microscopy, X-ray photoelectron spectroscopy, and field-emission scanning electron microscopy. The electrochemical properties were evaluated using cyclic voltammetry, electrochemical impedance spectroscopy, and galvanostatic charge–discharge tests. Structural analysis revealed a homogeneous distribution of nanosized TiO₂ particles on graphene nanosheets. The material exhibited a high specific capacitance of 165 F g⁻¹ at a scan rate of 5 mV s⁻¹ in 1 M Na₂SO₄ electrolyte solution. Theenhanced supercapacitance property of these materials could be ascribed to the increased conductivity of TiO₂ and better utilization of graphene. Moreover, the material exhibited long-term cycle stability, retaining ∼90% specific capacitance after 5000 cycles, which suggests that it has potential as an electrode material for high-performance electrochemical supercapacitors.     

High performance binder-free quaternary composite CuO/Cu/TiO2NT/Ti anode for lithium ion battery

High performance binder-free quaternary composite CuO/Cu/TiO₂ nanotube/Ti (CuO/Cu/TiO₂NT/Ti) electrode for lithium ion battery was designed and synthesized via anodization, electrodeposition and thermal oxidation at 450 °C in the air. The as-prepared binder-free quaternary composite CuO/Cu/TiO₂NT/Ti electrode was studied in terms of XRD, XPS, SEM, EDX, galvanostatic charge/discharge, cycle stability, cyclic voltammetry (CV) and AC impedance. As expected, the binder-free quaternary composite CuO/Cu/TiO₂NT/Ti electrode displayed much higher discharge capacity, cycle stability, Li⁺ diffusion coefficient than bare TiO₂NT/Ti electrode. High Li-storage activity of CuO, high conductivity of Cu and the synergy effect among various components should be responsible for improved electrochemical performances. Additionally, binder-free combination of the various components may also contribute into the modifications due to the exclusion of negative effect of polymer binder.     

Nanodiamond particles/reduced graphene oxide composites as efficient supercapacitor electrodes

The paper reports on the preparation of reduced graphene oxide (rGO) modified with nanodiamond particles composites by a simple solution phase and their use as efficient electrode in electrochemical supercapacitors. The technique relies on heating aqueous solutions of graphene oxide (GO) and nanodiamond particles (NDs) at different ratios at 100 °C for 48 h. The morphological properties, chemical composition and electrochemical behavior of the resulting rGO/NDs nanocomposites were investigated using UV/vis spectrometry, Fourier transform infrared (FTIR) spectroscopy, Raman spectroscopy, transmission electron microscopy (TEM) and electrochemical means. The electrochemical performance, including the capacitive behavior of the rGO/NDs composites were investigated by cyclic voltammetry and galvanostatic charge/discharge curves at 1 and 2 A g⁻¹ in 1 M H₂SO₄. The rGO/ND matrix with 10/1 ratio displayed the best performance with a specific capacitance of 186 ± 10 F g⁻¹ and excellent cycling stability.     

Facile synthesis of NiMn2O4 nanosheet arrays grown on nickel foam as novel electrode materials for high-performance supercapacitors

Nanostructured spinel NiMn₂O₄ arrays have been fabricated by a facile hydrothermal approach and further investigated as binder-free electrode for high-performance supercapacitors. Compared with Mn₃O₄, NiMn₂O₄ exhibited higher specific capacitances (662.5 F g⁻¹ and 370.5 F g⁻¹ in different electrolytes at the current density of 1 A g⁻¹) and excellent cycling stability (~96% capacitance retention after 1000 cycles) in a three-electrode system. Such a novel microstructure grown directly on the conductive substrate provided sufficient active sites for redox reaction resulting in their enhanced electrochemical behaviors. Their improved performances suggested that ultrathin sheet-like NiMn₂O₄ arrays on Ni foam substrate were a promising electrode material for supercapacitors.     

Carbon-coated SiO/ZrO2 composites as anode materials for lithium-ion batteries

A combination of high-energy ball milling and constant pressure chemical vapor deposition was used to prepare carbon-coated SiO/ZrO₂ composites. It was found that the as-prepared composites were composed of amorphous carbon, amorphous SiO, and paracryslalline ZrO₂. The electrochemical analysis results revealed excellent electrochemical performances for the composites, including a high initial discharge capacity (1737 mA h g⁻¹), a remarkable cyclic stability (reversible capacity of 721 mA h g⁻¹ at 800 mA g⁻¹, after 100 cycles), and a good rate capability (870 mA h g⁻¹ at 800 mA g⁻¹). These features demonstrate that these composites are promising alternative candidates for high-efficiency electrode materials of Li-ion batteries.     

Facile synthesis of Sm2S3 diffused nanoflakes and their pseudocapactive behavior

The Sm₂S₃ thin films with diffused nanoflakes morphology are prepared by an environment-friendly facile chemical synthesis method and used in electrochemical supercapacitors. The structural, elemental and surface morphological characterization are carried out using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FESEM) and wettability techniques. The FESEM images show tree root like distribution of flakes with average flake width of about 80 nm. The film surface is lyophilic with propylene carbonate contact angle of 21°. The supercapacitive measurements are carried out through cyclic voltammetry, galvanostatic charge-discharge and electrochemical impedance spectroscopy (EIS) techniques. The Sm₂S₃ film electrode exhibited a highest specific capacitance (C_s) of 213 Fg⁻¹ at 5 mVs⁻¹ scan rate in LiClO₄-propylene carbonate electrolyte. Asymmetric nature of charge–discharge curves confirmed pseudocapacitive behavior of electrode with energy and power densities of 39.39 Whkg⁻¹ and 4.33 kWkg⁻¹, respectively. An equivalent series resistance of 0.44 Ωcm⁻² indicated negligible ohmic losses in charge storage. An electrochemical stability of 81.47% is retained after 1000 cycles indicating that Sm₂S₃ is a promising candidate for supercapacitor application.     

A high capacity NiFe2O4/RGO nanocomposites as superior anode materials for sodium-ion batteries

NiFe₂O₄/reduced graphene oxide (NFO/RGO) nanocomposites were prepared by a facile one-step hydrothermal method and used as anode for sodium ion batteries (SIBs). The crystal structures, morphologies and electrochemical properties of as-prepared samples were evaluated by X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and galvanostatic charge/discharge tests. The results show that NFO/RGO-20 (20 wt%) delivers the highest reversible capacity of ~450 mA h g⁻¹ at 50 mA g⁻¹ after 50 cycles with good cycling stability. The excellent sodium storage performance of NFO/RGO should be attributed to the synergistic effect between NFO and RGO to form conductive network structure, which offers the increased specific surface area, the facilitated electron transfer ability and the buffering of volume expansion.     

Electrochemical energy storage performance of heterostructured SnO2@MnO2 nanoflakes

In this work, we report synthesis of SnO₂@MnO₂ nanoflakes grown on nickel foam through a facile two-step hydrothermal route. The as-obtained products are characterized by series of techniques such as scanning electron microscopy (SEM), X-ray diffraction spectroscopy (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The as-obtained SnO₂@MnO₂ nanoflakes are directly used as supercapacitor electrode materials. The results show that the electrode possesses a high discharge areal capacitance of 1231.6 mF cm⁻² at 1 mA cm⁻² and benign cycling stability with 67.2% of initial areal capacitance retention when the current density is 10 mA cm⁻² after 6000 cycles. Moreover, the heterostructured electrode shows 41.1% retention of the initial capacitance when the current densities change from 1 to 10 mA cm⁻², which reveals good rate capability. SnO₂@MnO₂ nanoflakes products which possess excellent electrochemical properties might be used as potential electrode materials for supercapacitor applications.     

The additive-free electrode based on the layered MnO2 nanoflowers/reduced,graphene oxide film for high performance supercapacitor

The MnO₂ nanoflowers/reduced graphene oxide composite is coated on a nickel foam substrate (denoted as MnO₂ NF/RGO @ Ni foam) via the layer by layer (LBL) self-assembly technology without any polymer additive, following the soft chemical reduction. The layered MnO₂ NF/RGO composite is uniformly anchored on the Ni foam skeleton to form the 3D porous framework, and the interlayers have access to lots of ions channels to improve the electron transfer and diffusion. This special construction of 3D porous structure is beneficial to the enhancement of electrochemical property. The specific capacitance is up to 246 F g⁻¹ under the current density of 0.5 A g⁻¹. After 1000 cycles, it can retain about 93%, exhibiting excellent cycle stability. The electrochemical impedance spectroscopy measurements confirm that MnO₂ NF/RGO @ Ni foam electrode has lower R_ESR and R_CT values when compared to MnO₂ @ Ni foam and RGO @ Ni foam. This study opens a new door to the preparation of composite electrodes for high performance supercapacitor.     

Network structures of fullerene-like carbon core/nano-crystalline silicon shell nanofibers as anode material for lithium-ion batteries

Fullerene-like carbon (FLC) nanoparticles were prepared by depositing soot of burning castor oil. FLC core/nano-crystalline silicon (nc-Si) shell nanofibers with network structures have been fabricated by electrospinning and plasma enhanced chemical vapor deposition techniques. The morphologies and structures of the materials were characterized using scanning electron microscopy, transmission electron microscopy, and micro-Raman spectroscopy. It was demonstrated that the FLC core/nc-Si shell nanofibers on nickel foam can be used as electrode for lithium-ion batteries without adding any binding or conducting additives. High reversible specific capacity of 1164 mA h g⁻¹ is retained after 50 discharge/charge cycles at a constant current density of 100 mA g⁻¹. The electrode delivers prolonged cycle life and enhanced rate capability compared to pristine nc-Si film. The improved electrochemical performance could be attributed to that the FLC core provides facile strain relaxation to accommodate the large Si volume expansion and shrinkage during lithium-ion insertion and extraction.     

Hierarchical Co3O4@ZnWO4 core/shell nanostructures on nickel foam: Synthesis and electrochemical performance for supercapacitors

To improve the electrochemical properties of Co₃O₄ for supercapacitors application, a hierarchical Co₃O₄@ZnWO₄ core/shell nanowire arrays (NWAs) material is designed and synthesized successfully via a facile two-step hydrothermal method followed by the heat treatment. Co₃O₄@ZnWO₄ NWAs exhibits excellent electrochemical performances with areal capacitance of 4.1 F cm⁻² (1020.1 F g⁻¹) at a current density of 2 mA cm⁻² and extremely good cycling stability (99.7% of the initial capacitance remained even after 3000 cycles). Compared with pure Co₃O₄ electrodes, the results prove that this unique hierarchical hybrid nanostructure and reasonable assembling of two electrochemical pseudocapacitor materials are more advantageous to enhance the electrochemical performance. Considering these remarkable capacitive behaviors, the hierarchical Co₃O₄@ZnWO₄ core/shell NWAs nanostructure electrode can be revealed promising for high-performance supercapacitors.     

Effects of acid vapour mediated oxidization on the electrochemical performance of thermally exfoliated graphene

The surface modification of thermally exfoliated graphene (TEG) is an important technique for alteration of its hydrophobic nature and the resolution of its limited dispersibility. We have developed an easy acid-vapour-mediated method to functionalize the inert TEG surface with oxygen functional groups. The effects of oxygen functional groups on the capacitive performances of TEG were investigated with various reaction times. Ultraviolet–visible, Fourier transform infrared and Raman spectroscopy analyses demonstrated that the dispersibility of TEG was improved due to defect augmenting as the extent of oxidation progressed. Quantitative analyses of functional groups of the oxidized TEG samples (O-TEGs) were performed by thermogravimetric analysis and X-ray photoelectron spectroscopic studies. Physisorption surface analysis showed that the pore volumes of O-TEGs were greater than that of the pristine TEG, whereas the specific surface areas of O-TEGs were lower than that of pristine TEG. Electrochemical performances of the O-TEG samples were measured through cyclic voltammetry, galvanostatic charge–discharge, and electrochemical impedance spectroscopy analysis. A maximum specific capacitance of 175.2 F g⁻¹ was recorded at a current density of 1 A g⁻¹ for the O-TEG oxidized for 2 h. Retention of specific capacitance for the sample was ∼97% after 5000 charge–discharge cycles.