Low reversion of lithium sulfide and defects causing irreversible capacity loss are the primary causes of low Coulombic efficiency in tin sulfide/graphene-based composites. Herein, we synthesized a SnS/graphene composite via a novel lithiation-assisted exfoliation and reduction method using SnS2, n-butyllithium, and graphene oxide as raw materials. The experimental results reveal that lithium from the insertion agent combine with the oxygen-containing groups on graphene oxide; this can help in the reduction of hexagonal SnS2 to orthorhombic SnS during calcination and simultaneous pre-occupancy of the edge and defect sites of graphene; thus, additional lithium ion consumption during the initial several lithiation processes is diminished. Microstructural characterizations indicate that the exfoliated SnS nanosheets with a dramatically decreased lateral size (50–100 nm) are uniformly decorated on the surface of lithium-integrated graphene sheets. Consequently, the as-prepared SnS/graphene composite exhibits a significantly high SnS ultilization with a 77.5% initial Coulombic efficiency, which is the highest value reported in the current literature. Moreover, an excellent reversibility of conversion reaction (SnS + 2Li+ + 2e− ↔ Sn + Li2S) and a high reversible capacity of 1016.4 mA h g−1 after 100 cycles are expressed in this composite electrode, demonstrating its importance as an anode material for energy storage.

Three-dimensional (3D) interconnected spherical graphene framework-decorated SnS nanoparticles (3D SnS@SG) is synthesized by self-assembly of graphene oxide nanosheets and positively charged polystyrene/SnO2 nanospheres, followed by a controllable in situ sulfidation reaction during calcination. The SnS nanoparticles with diameters of ∼10–30 nm are anchored to the surface of the spherical graphene wall tightly and uniformly. Benefiting from the 3D interconnected spherical graphene framework and subtle SnS nanoparticles, the generated Li2S could keep in close contact with Sn to make possible the in situ conversion reaction SnS + 2Li+ + 2e– ↔ Sn + Li2S. As a result, the 3D SnS@SG as the anode material for lithium ion batteries shows a high initial Coulombic efficiency of 75.3%. Apart from the irreversible capacity loss of 3D spherical graphene, the initial Coulombic efficiency of SnS in the 3D SnS@SG composite is as high as 99.7%, demonstrating the almost complete reversibility of Li2S in this system. Furthermore, it also exhibits an excellent reversible capacity (800 mAh g–1 after 100 cycles at 0.1 C and 527.1 mAh g–1 after 300 cycles at 1 °C) and outstanding rate capability (380 mAh g–1 at 5 °C).Keywords: Coulombic efficiency; energy storage; interconnected spherical graphene; lithium sulfide; three-dimensional; tin sulfide;

•A novel core-shell Li2S@Li3PS4 composite is reported as cathode for Li-S battery.•It comprises highly crystal nano-Li2S and superionic conducting Li3PS4 coating layer.•The Li2S@Li3PS4/GA electrode shows low potential barrier (2.40 V) and overpotential.•The composite delivers high specific capacity of 934.4 mA h/g at 0.1 C rate.Lithium sulfide as a promising cathode material not only have a high theoretical specific capacity, but also can be paired with Li-free anode material to avoid potential safety issues. However, how to prepare high electrochemical performance material is still challenge. Herein, we present a facile way to obtain high crystal quality Li2S nanomaterials with average particle size of about 55 nm and coated with Li3PS4 to form the nano-scaled core-shell Li2S@Li3PS4 composite. Then nano-Li2S@Li3PS4/graphene aerogel is prepared by a simple liquid infiltration-evaporation coating process and used directly as a composite cathode without metal substrate for lithium-sulfur batteries. Electrochemical tests demonstrate that the composite delivers a high discharge capacity of 934.4 mAh g−1 in the initial cycle and retains 485.5 mAh g−1 after 100 cycles at 0.1 C rate. In addition, the composite exhibits much lower potential barrier (∼2.40 V) and overpotential compared with previous reports, indicating that Li2S needs only a little energy to be activated. The excellent electrochemical performances could be attributed to the tiny particle size of Li2S and the superionic conducting Li3PS4 coating layer, which can shorten Li-ion and electron diffusion paths, improve the ionic conductivity, as well as retarding polysulfides dissolution into the electrolyte to some extent.A novel core-shell Li2S@Li3PS4 composite with highly crystal nano-Li2S particles (ca. 55 nm) and superionic conducting Li3PS4 coating layer is introduced, and it shows low potential barrier (∼2.40 V) and overpotential as cathode for Li–S battery.Download high-res image (245KB)Download full-size image

•3D hierarchical ultrathin MnO2/graphene is first prepared by ultrasonic-assisted co-precipitation method.•Time-dependent experiments are carried out to investigate formation mechanism.•Hierarchical MnO2 is formed through self-assembly and Ostwald ripening process.•The composite delivers a capacitance of 216 F g−1 at 1 A g−1 with capacity retention of 89.3% after 2000 cycles.Hierarchical ultrathin nanostructure MnO2 on graphene sheets are first prepared through ultrasonic-assisted co-precipitation method. The possible growth mechanism of the nanocomposite is discussed by monitoring the early growth stages. It is shown that the formation of the hierarchical structure MnO2 follows a typical self-assembly and Ostwald ripening process. The dispersion of nanoscale thin MnO2 flakes with thicknesses of about 5–10 nm on the graphene helped to increase the contact area of MnO2 with electrolyte, reduce the diffusion and migration length of the ions and increase the electrochemical utilization of MnO2. Electrochemical characterization demonstrate that the hierarchical MnO2/graphene are capable of delivering specific capacitance of 216 F g−1 at the current density of 1 A g−1. A capacity retention of 89.3% can be maintained after 2000 continuous charge–discharge cycles. The method provides a facile and straightforward approach to synthesize hierarchical of MnO2 onto the graphene and may be readily extended to the preparation of other classes of hybrids based on graphene sheets for technological applications.Download high-res image (529KB)Download full-size image

•3D hierarchical NiO/graphene is prepared by a refluxing method with aqua-based solvent.•Time-dependent experiments are carried out to investigate formation mechanism.•Hierarchical sphere is formed through self-assembly of NiO grown on disc-shaped CTAB micelles.•It delivers a capacitance of 555 F g−1 at 1 A g−1 with 90.8% retention after 2000 cycles.This article reports a facile preparation of NiO/graphene composite by the combination of a controlled refluxing method with water based solvent in the presence of cetyltrimethylammonium bromide and subsequent annealing. X-ray diffraction and scanning electron microscopy reveal that the graphene nanosheets are uniformly wrapped by hierarchical porous NiO spheres with three-dimension hierarchical structure in the product. The composite shows highly improved electrochemical performance as electrode material for supercapacitor. The three-dimension hierarchical structure NiO/graphene composite delivers a first discharge capacitance of 555 F g−1 and remains a reversible capacitance up to 504 F g−1 after 2000 cycles at a current of 1 A g−1 in three-electrode system. Contrarily, the pure NiO shows only a first discharge capacitance of 166 F g−1 and remains only a reversible capacitance of 107 F g−1 after 2000 cycles. The NiO/graphene composite also exhibits ameliorative rate capacitance of 402.9 F g−1 at the current density of 5 A g−1. The enhanced electrochemical performances are ascribed to the higher surface area, the stable three-dimension hierarchical structure and the synergistic effects between the conductive graphene and porous NiO spheres.Graphical abstract

In this study, a nanorod-like Fe2O3/graphene nanocomposite is synthesized by a facile template-free hydrothermal method and a following calcination in air at 300 °C for 2 h. The Fe2O3 nanorods with diameter of 15–30 nm and length of 120–300 nm are homogenous distributed on both sides of graphene. The morphologies of intermediates at different hydrothermal reaction times are investigated by transmission electron microscopy (TEM) characterization, and a possible growth mechanism of this one-dimensional structure is proposed. It is shown that the α-FeOOH rodlike precursors are formed through a rolling-broken-growth (RBG) model, then the α-FeOOH is transformed into α-Fe2O3 nanorods during calcinations, preserving the same rodlike morphology. Electrochemical characterizations demonstrate that the Fe2O3 nanorod/graphene composites exhibit a very large reversible capacity of 1063.2 mAh/g at the charge/discharge rate of 0.1 C.

In this paper, a leaf-like porous CuO–graphene nanostructure is synthesized by a hydrothermal method. The as-prepared composite is characterized using XRD, Raman, SEM, TEM and nitrogen adsorption–desorption. The growth mechanism is discussed by monitoring the early growth stages. It is shown that the CuO nanoleaves are formed through oriented attachment of tiny Cu(OH)2 nanowires. Electrochemical characterization demonstrates that the leaf-like CuO–graphene are capable of delivering specific capacitances of 331.9 and 305 F g−1 at current densities of 0.6 and 2 A g−1, respectively. A capacity retention of 95.1% can be maintained after 1000 continuous charge–discharge cycles, which may be attributed to the improvement of electrical contact by graphene and mechanical stability by the layer-by-layer structure. The method provides a facile and straightforward approach to synthesize CuO nanosheets on graphene and may be readily extended to the preparation of other classes of hybrids based on graphene sheets for technological applications.

In this paper, graphene sheets with different reduction levels have been produced through thermal reduction of graphene oxide in the temperature range of 200–900 °C. The effects of interlayer spacing, oxygen content, BET specific surface area and disorder degree on their specific capacitance were explored systematically. The variation of oxygen-containing groups was shown to be a main factor influencing the EDL capacitor performances of the pyrolytic graphene. The highest capacitance of 260.5 F g−1 at a charge/discharge current density of 0.4 A g−1 was obtained for the sample thermally reduced at about 200 °C.Highlights► Graphene with different reduction levels is produced through thermal reduction of GO. ► Oxygen content increases and interlayer spacing of pyrolysis GO decreases with temperature. ► Raising reduction temperature results in a lower ID/IG ratio and red-shift of G peak in Raman spectra. ► GO prepared at 200 °C delivers the highest specific capacitance of 260.5 F g−1. ► Oxygen content is shown to be a main factor influencing the EDL capacitor of pyrolysis graphene.

Porous NiO nanosheet has been synthesized by hydrothermal method, using Ni(NO3)2·6H2O and urea as the raw materials and DI water as solvent, then followed by calcination process. It has been indicated by TEM and BET analysis that the as-prepared NiO was porous nanosheet. With the increase of annealing temperature, the pore size on the nanosheet becomes larger and the specific surface area becomes much smaller. All isotherms of NiO display type IV with H3 type hysteresis loop with pore size distribution of 2–60 nm. The annealing temperature turns out to be the key factor to pore size, pore distribution and pore volume.Highlights► Porous NiO nanosheet was prepared via hydrothermal method. ► With increase of annealing temperature, the surface area become much smaller and pore size gets larger. ► The annealing temperature is the key factor to control pore size, distribution and pore volume.

In this paper, graphene oxide (GO) synthesized from the modified Hummer method is used directly to fabricate unique two-dimension graphene/NiO composite material. Nickel ions are adsorbed on both sides of GO based on self-assembly by the electrostatic interactions of two species, forming the monolayer graphene/NiO sheet. The as-prepared composite is characterized using X-ray diffraction (XRD), Raman, SEM, TEM, Energy Dispersive Spectrometer (EDS) analysis and nitrogen adsorption/desorption. The results demonstrate that the NiO nanoparticles (5–7 nm) is uniformly dispersed on the surface of graphene, which greatly increases the surface area of the composite (134.5 m2 g−1). This two-dimensional structure enhances supercapacitive performance with a high specific capacitance of 525 F g−1 at a current density of 200 mA g−1. A capacity retention of 95.4% can be maintained after 1000 cycles, suggesting its promising potential in supercapacitors.

Co-precipitation method of SnCl2·2H2O and graphene oxide (GO) solution was performed to fleetly prepare graphene/SnO2 composite. The structure and composition of the nanocomposite were detected by means of XRD, SEM, TEM and FT-IR. The GO was reduced by bivalent tin ions to graphene nanosheet (GNS) via solution reaction and SnO2 nano-crystals with size of 4–6 nm were homogeneously distributed on the matrix of GNS. It was found that the disorder degree of graphene in GNS/SnO2 composite prepared by the bivalent tin ion assisted reduction method was much lower than that of GNS obtained via pyrolysis reduction. The possible mechanism for this phenomenon was discussed in detail. The N2 adsorption tests showed an ink-bottle-like pore structure of GNS/SnO2 and the SnO2 nanoparticles were confined in the interlayer of GNS without agglomeration. These structural features were desirable and enabled GNS/SnO2 an excellent anode material in lithium ion battery. The electrochemical tests showed that the composite could deliver a reversible capacity of 775.3 mAh/g and capacity retention of 98% after 50 cycles.Highlights• Graphene/SnO2 composite was prepared via bivalent tin ion assisted reduction method. • The SnO2 nanoparticles were homogeneously distributed on the matrix of graphene sheets, forming an ink-bottle-like pores structure. • The disorder degree of graphene in GNS/SnO2 was obviously diminished. • The composite could deliver a reversible capacity of 775.3 mAh/g and capacity retention of 98% after 50 cycles.

In this paper, graphene oxide (GO) synthesized from the modified Hummer method is used directly to fabricate unique two-dimension graphene/NiO composite material. Nickel ions are adsorbed on both sides of GO based on self-assembly by the electrostatic interactions of two species, forming the monolayer graphene/NiO sheet. The as-prepared composite is characterized using X-ray diffraction (XRD), Raman, SEM, TEM, Energy Dispersive Spectrometer (EDS) analysis and nitrogen adsorption/desorption. The results demonstrate that the NiO nanoparticles (5–7 nm) is uniformly dispersed on the surface of graphene, which greatly increases the surface area of the composite (134.5 m2 g−1). This two-dimensional structure enhances supercapacitive performance with a high specific capacitance of 525 F g−1 at a current density of 200 mA g−1. A capacity retention of 95.4% can be maintained after 1000 cycles, suggesting its promising potential in supercapacitors.

In this paper, a leaf-like porous CuO–graphene nanostructure is synthesized by a hydrothermal method. The as-prepared composite is characterized using XRD, Raman, SEM, TEM and nitrogen adsorption–desorption. The growth mechanism is discussed by monitoring the early growth stages. It is shown that the CuO nanoleaves are formed through oriented attachment of tiny Cu(OH)2 nanowires. Electrochemical characterization demonstrates that the leaf-like CuO–graphene are capable of delivering specific capacitances of 331.9 and 305 F g−1 at current densities of 0.6 and 2 A g−1, respectively. A capacity retention of 95.1% can be maintained after 1000 continuous charge–discharge cycles, which may be attributed to the improvement of electrical contact by graphene and mechanical stability by the layer-by-layer structure. The method provides a facile and straightforward approach to synthesize CuO nanosheets on graphene and may be readily extended to the preparation of other classes of hybrids based on graphene sheets for technological applications.