Chunli Guo

Facile Synthesis of Hierarchical Mesoporous Honeycomb-like NiO for Aqueous Asymmetric Supercapacitors

Three-dimensional (3D) hierarchical nanostructures have been demonstrated as one of the most ideal electrode materials in energy storage systems due to the synergistic combination of the advantages of both nanostructures and microstructures. In this study, the honeycomb-like mesoporous NiO microspheres as promising cathode materials for supercapacitors have been achieved using a hydrothermal reaction, followed by an annealing process. The electrochemical tests demonstrate the highest specific capacitance of 1250 F g(-1) at 1 A g(-1). Even at 5 A g(-1), a specific capacitance of 945 F g(-1) with 88.4% retention after 3500 cycles was obtained. In addition, the 3D porous graphene (reduced graphene oxide, rGO) has been prepared as an anode material for supercapacitors, which displays a good capacitance performance of 302 F g(-1) at 1 A g(-1). An asymmetric supercapacitor has been successfully fabricated based on the honeycomb-like NiO and rGO. The asymmetric supercapacitor achieves a remarkable performance with a specific capacitance of 74.4 F g(-1), an energy density of 23.25 Wh kg(-1), and a power density of 9.3 kW kg(-1), which is able to light up a light-emitting diode.

Facile synthesis of mesoporous Mn3O4 nanotubes and their excellent performance for lithium-ion batteries

Because of the low cost and operating potential, Mn3O4 is highly noticeable among transition metal oxides as an anode material for Li-ion batteries. Here, mesoporous Mn3O4 nanotubes with a high surface area of 42.18 m2 g−1 and an average pore size of 3.72 nm were synthesized for the first time through the hydrogen reduction of β-MnO2 nanotubes under a H2/Ar atmosphere at 280 °C for 3 h. Electrochemical results demonstrate that the reversible capacity of mesoporous Mn3O4 nanotubes is 641 mA h g−1 (much higher than the theoretical capacity of graphite, ∼372 mA h g−1) after 100 cycles at a high current density of 500 mA g−1. The superior electrochemical performance can be attributed to the unique 1D mesoporous nano-tubular structure, which offers fast and flexible transport pathways for electrolyte ions, and also provides sufficient free space to buffer the large volume change of anodes based on the conversion reaction during the repeated lithium-ion insertion/extraction. The improved electrochemical performance makes such a mesoporous Mn3O4 tubular structure promising as an anode material for next-generation lithium-ion batteries.

MOFs-derived porous Mn2O3 as high-performance anode material for Li-ion battery

MOFs-derived porous Mn2O3 have been synthesized by the high-temperature calcination of a metal–organic framework, [Mn(Br4-bdc)(4,4′-bpy)(H2O)2]n (Br4-bdc = tetrabromoterephthalate and 4,4′-bpy = 4,4′-bipyridine). The porous Mn2O3 as an anode material for lithium ion batteries displays excellent performances, 705 mA h g−1 after 250 cycles at 1 A g−1.

Facile synthesis of mesoporous Mn3O4 nanorods as a promising anode material for high performance lithium-ion batteries

In this work, porous Mn3O4 nanorods have been fabricated through the decomposition of MnOOH nanorods under an inert gas. The sample shows a high BET surface area of 27.6 m2 g−1 and a narrow pore size distribution of 3.9 nm. Because of the excellent porous geometry and one-dimensional structure, the porous Mn3O4 nanorods display outstanding electrochemical performance, such as high specific capacity (901.5 mA h g−1 at a current density of 500 mA g−1), long cycling stability (coulombic efficiency of 99.3% after 150 cycles) and high rate capability (387.5 mA h g−1 at 2000 mA g−1). Very interestingly, the porous Mn3O4 nanorods are converted to Mn3O4 following electrochemical reaction, which does not occur with nonporous Mn3O4 nanorods. The possible reason may be ascribed to the improved kinetics of the porous structure.

Well-shaped Mn3O4 tetragonal bipyramids with good performance for lithium ion batteries

Well-shaped Mn3O4 tetragonal bipyramids with a high reversible capacity of 822.3 mA h g−1 are synthesized by a simple hydrothermal method without any surfactants or coordination compounds. The structural features and morphology of the final product are investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM). The SEM and HRTEM results reveal that all the eight exposed facets of the Mn3O4 tetragonal bipyramids are indexed to the high-energy {101} planes. The tetragonal bipyramids with high-energy facets provide the Mn3O4 anode material with a high initial discharge capacity (1141.1 mA h g−1). In addition, the anode displays a good fast rate performance, delivering a reversible capacity of 822.3 mA h g−1 (the theoretical capacity: 937 mA h g−1) at a current density of 0.2 C after 50 cycles. Moreover, the coulomb efficiency for the first cycle reaches about 66% and remains at about 100% during the subsequent cycles. A relatively detailed growth mechanism of these tetragonal bipyramids is proposed in this manuscript.

Hierarchical MoS2@Carbon Microspheres as Advanced Anodes for Li-Ion Batteries

Hierarchical hybridized nanocomposites with rationally constructed compositions and structures have been considered key for achieving superior Li-ion battery performance owing to their enhanced properties, such as fast lithium ion diffusion, good collection and transport of electrons, and a buffer zone for relieving the large volume variations during cycling processes. Hierarchical MoS2 @carbon microspheres (HMCM) have been synthesized in a facile hydrothermal treatment. The structure analyses reveal that ultrathin MoS2 nanoflakes (ca.u20052-5u2005nm) are vertically supported on the surface of carbon nanospheres. The reversible capacity of the HMCM nanocomposite is maintained at 650u2005mAu2009hu2009g(-1) after 300 cycles at 1u2005Au2009g(-1) . Furthermore, the capacity can reach 477u2005mAu2009hu2009g(-1) even at a high current density of 4u2005Au2009g(-1) . The outstanding electrochemical performance of HMCM is attributed to the synergetic effect between the carbon spheres and the ultrathin MoS2 nanoflakes. Additionally, the carbon matrix can supply conductive networks and prevent the aggregation of layered MoS2 during the charge/discharge process; and ultrathin MoS2 nanoflakes with enlarged surface areas, which can guarantee the flow of the electrolyte, provide more active sites and reduce the diffusion energy barrier of Li(+) ions.

Fabrication of Various V2O5 Hollow Microspheres as Excellent Cathode for Lithium Storage and the Application in Full Cells

Vanadium pentoxide (V2O5) has attracted interesting attention as cathode material for LIBs because of its stable crystal structure and high theoretical specific capacity. However, the low rate performance and poor long-term cycling stability of V2O5 limit its applications. In order to improve its battery performance, various V2O5 hollow microspheres including a yolk-shell structure, double-shell structure, triple-shell structure, and hierarchical hollow superstructures have been selectively prepared. The obtained hierarchical V2O5 hollow microspheres (HVHS) exhibit a high capacity of 123 mAh g(-1) at 20 C (1 C = 147 mA g(-1)) in the range of 2.5-4.0 V, and 73.5 mAh g(-1) can be reached after 3000 cycles. HVHS also display good cycling performance in the range of 2.0-4.0 V. Moreover, the V2O5//Li4Ti5O12 full cell was successfully assembled, which exhibits an excellent performance of 139.5 mAh g(-1) between 1.0 and 2.5 V at a current density of 147 mA g(-1), and a high capacity of 106 mAh g(-1) remained after 100 cycles, indicating the good cycling performance and promising application of the full cell.

Doping Ni: an effective strategy enhancing electrochemical performance of MnCO3 electrode materials for supercapacitors

Ni-doped MnCO3 microspheres were successfully synthesized via a one-step mixed solvent-thermal method. The as-prepared samples were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and N2 adsorption–desorption measurements. The fabricated Ni-doped MnCO3 microspheres exhibited a higher specific capacity (538xa0Fxa0g−1 at a current density of 1xa0Axa0g−1) than pure MnCO3 (287xa0Fxa0g−1). In addition, 85.8xa0% of initial capacity was retained after 3000 cycles at a current density of 5xa0Axa0g−1, demonstrating a good cycling performance. These results suggested that Ni-doped MnCO3 microspheres material was a promising candidate for high energy storage applications. Hence doping heterogeneous element with good electrical conductivity was an effective approach to improve the electrochemical performance of the electrode materials.

Evaluation on Fatigue Performance and Fracture Mechanism of Laser Welded TWIP Steel Joint Based on Evolution of Microstructure and Micromechanical Properties

The fatigue performance and fracture mechanism of laser welded twinning induced plasticity (TWIP) steel joint were investigated experimentally based on the evolution of microstructure and micromechanical properties. The optical microscopy was used to analyze the evolution of microstructure. The variation of composition and phase structure of fusion zone were detected by energy dispersive X-ray and X-ray diffraction spectrometers. The micromechanical behaviors of the various zones were characterized using nanoindentation. The static tensile test and high cycle fatigue test were performed to evaluate the mechanical properties of welded joint and base metal. The microstructures, tensile properties and fatigue strength of base metal as well as welded metal were analyzed. The fatigue fracture surfaces of base metal and welded joint were observed by means of scanning electron microscopy, in order to identify fatigue crack initiation sites and propagation mechanisms. Moreover, the fatigue fracture characteristics and mechanisms for the laser welded TWIP steel joints were analyzed.

Synthesis of Mesoporous Co3O4/NiCo2O4 Nanorods and Their Electrochemical Study

Mesoporous Co₃O₄/NiCo₂O₄ nanorods were obtained by a hydrothermal reaction with the assistance of Ni foam and subsequent annealing treatment. The characterization of this composition by X-ray diffraction, X-ray photoelectron spectroscopy, high-resolution transmission electron microscopy, energy dispersive spectra and Brunauer-Emmett-Teller analysis revealed that the nanorods consisted of Co₃O₄ and NiCo₂O₄ phase, exhibiting high porosity and rich crystal defects. The electrochemical data showed a specific capacitance of 1173 mF cm-2 and 606 mF cm-2 at 2 mV s-1 and 1 mA cm-2, respectively. Its cycling performance was 83.9% at 3 mA cm-2 after 4000 cycles. Furthermore, the asymmetric supercapacitor Co₃O₄/NiCo₂O₄//AC delivered an energy density of 11.7 W h kg-1 and power density of 760 W kg-1.