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Chen S.,The Clean Tech Center | Bao P.,University of Sydney | Huang X.,The Clean Tech Center | Sun B.,The Clean Tech Center | Wang G.,The Clean Tech Center
Nano Research | Year: 2014

Silicon has been recognized as the most promising anode material for high capacity lithium ion batteries. However, large volume variations during charge and discharge result in pulverization of Si electrodes and fast capacity loss on cycling. This drawback of Si electrodes can be overcome by combination with well-organized graphene foam. In this work, hierarchical three-dimensional carbon-coated mesoporous Si nanospheres@graphene foam (C@Si@GF) nanoarchitectures were successfully synthesized by a thermal bubble ejection assisted chemical-vapor-deposition and magnesiothermic reduction method. The morphology and structure of the as-prepared nanocomposites were characterized by field emission scanning electron microscopy, transmission electron microscopy and Raman spectroscopy. When employed as anode materials in lithium ion batteries, C@Si@GF nanocomposites exhibited superior electrochemical performance including a high specific capacity of 1,200 mAh/g at the current density of 1 A/g, excellent high rate capabilities and an outstanding cyclability. Post-mortem analyses identified that the morphology of 3D C@Si@GF electrodes after 200 cycles was well maintained. The synergistic effects arising from the combination of mesoporous Si nanospheres and graphene foam nanoarchitectures may address the intractable pulverization problem of Si electrode. [Figure not available: see fulltext.] © 2014 Tsinghua University Press and Springer-Verlag Berlin Heidelberg.


Su D.,The Clean Tech Center | Wang C.,Yangzhou University | Ahn H.,Gyeongsang National University | Wang G.,The Clean Tech Center
Physical Chemistry Chemical Physics | Year: 2013

Single crystalline SnO2 nanocrystals (∼60 nm in size) with a uniform octahedral shape were synthesised using a hydrothermal method. Their phase and morphology were characterized by XRD and FESEM observation. TEM and HRTEM analyses identified that SnO2 octahedral nanocrystals grow along the [001] direction, consisting of dominantly exposed {221} high energy facets. When applied as anode materials for Na-ion batteries, SnO2 nanocrystals exhibited high reversible sodium storage capacity and excellent cyclability (432 mA h g-1 after 100 cycles). In particular, SnO 2 nanocrystals also demonstrated a good high rate performance. Ex situ TEM analysis revealed the reaction mechanism of SnO2 nanocrystals for reversible Na ion storage. It was found that Na ions first insert into SnO2 crystals at the high voltage plateau (from 3 V to ∼0.8 V), and that the exposed (1 × 1) tunnel-structure could facilitate the initial insertion of Na ions. Subsequently, Na ions react with SnO2 to form NaxSn alloys and Na2O in the low voltage range (from ∼0.8 V to 0.01 V). The superior cyclability of SnO 2 nanocrystals could be mainly ascribed to the reversible Na-Sn alloying and de-alloying reactions. Furthermore, the reduced Na2O "matrix" may help retard the aggregation of tin nanocrystals, leading to an enhanced electrochemical performance. This journal is © the Owner Societies 2013.


Su D.,The Clean Tech Center | Wang C.,Yangzhou University | Ahn H.-J.,Gyeongsang National University | Wang G.,The Clean Tech Center
Chemistry - A European Journal | Year: 2013

Single crystalline rhombus-shaped Na0.7MnO2 nanoplates have been synthesized by a hydrothermal method. TEM and HRTEM analyses revealed that the Na0.7MnO2 single crystals predominantly exposed their (100) crystal plane, which is active for Na +-ion insertion and extraction. When applied as cathode materials for sodium-ion batteries, Na0.7MnO2 nanoplates exhibited a high reversible capacity of 163 mA h g-1, a satisfactory cyclability, and a high rate performance. The enhanced electrochemical performance could be ascribed to the predominantly exposed active (100) facet, which could facilitate fast Na+-ion insertion/extraction during the discharge and charge process. © 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.


Chen S.,The Clean Tech Center | Bao P.,University of New South Wales | Wang G.,The Clean Tech Center
Nano Energy | Year: 2013

Fe2O3-CNT-graphene nanosheet (Fe2O3-CNT-GNS) hybrid materials were synthesized using a chemical vapor deposition method. The as-prepared materials consist of Fe2O3 nanorings, bamboo-like carbon nanotubes and graphene nanosheets, which form an open three-dimensional architecture. For the first time, we observed the growth of bamboo-like carbon nanotubes with open tips, which were catalyzed by iron nanorings. When applied as anode materials in lithium ion batteries, the Fe2O3-CNT-GNS hybrid materials exhibited a high specific capacity of 984mAhg-1 with a superior cycling stability and high rate capability. This could be ascribed to short Li+ diffusion path of bamboo-like CNTs, more active reaction sites provided by graphene layers inside CNTs, flexible and highly conductive graphene nanosheets, and an open three-dimensional structure. © 2012 Elsevier Ltd.


Su D.,The Clean Tech Center | Xie X.,The Clean Tech Center | Wang G.,The Clean Tech Center
Chemistry - A European Journal | Year: 2014

Mesoporous SnO microspheres were synthesised by a hydrothermal method using NaSO4 as the morphology directing agent. Field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM) analyses showed that SnO microspheres consist of nanosheets with a thickness of about 20anm. Each nanosheet contains a mesoporous structure with a pore size of approximately 5anm. When applied as anode materials in Na-ion batteries, SnO microspheres exhibited high reversible sodium storage capacity, good cyclability and a satisfactory high rate performance. Through ex situ XRD analysis, it was found that Na+ ions first insert themselves into SnO crystals, and then react with SnO to generate crystalline Sn, followed by Na-Sn alloying with the formation of crystalline NaSn2 phase. During the charge process, there are two slopes corresponding to the de-alloying of Na-Sn compounds and oxidisation of Sn, respectively. The high sodium storage capacity and good electrochemical performance could be ascribed to the unique hierarchical mesoporous architecture of SnO microspheres. Let it SnO: Hierarchical mesoporous SnO microspheres were synthesised by a hydrothermal method using NaSO 4 as the morphology directing agent. When applied as anode materials for Na-ion batteries, they exhibited high reversible sodium storage capacity and excellent cyclability. The good electrochemical performance could be ascribed to the unique hierarchical mesoporous architecture of SnO microspheres (see graphic). © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Su D.,The Clean Tech Center | Wang G.,The Clean Tech Center
ACS Nano | Year: 2013

Single-crystalline bilayered vanadium oxide nanobelts were synthesized by a simple solvothermal method. FESEM and AFM analyses identified the nanobelt morphology of the as-prepared vanadium oxide with a rectangular cross-section and a thickness of approximately 50 nm. XRD and TEM characterizations revealed the presence of a large (001) interlayer spacing (∼11.53 Å), which can accommodate Na-ion insertion and extraction. When applied as cathode materials in Na-ion batteries, vanadium oxide nanobelts exhibited a high capacity of 231.4 mA h g-1 at a current density of 80 mA g-1. This corresponds to the theoretical capacity to form Na2V 2O5 on Na-ion insertion. Vanadium oxide nanobelts also demonstrated an excellent high-rate performance and a satisfactory cyclability. These superior electrochemical performances could be ascribed to the unique bilayered vanadium oxide nanobelts with dominantly exposed {100} crystal planes, which provide large interlayer spacing for facile Na-ion insertion/extraction. Single-crystalline bilayered vanadium oxide nanobelts could be promising cathode materials for high-performance Na-ion batteries. © 2013 American Chemical Society.


Su D.,The Clean Tech Center | Ahn H.-J.,Gyeongsang National University | Wang G.,The Clean Tech Center
NPG Asia Materials | Year: 2013

Sodium-ion batteries are being considered as a promising system for stationary energy storage and conversion, owing to the natural abundance of sodium. It is important to develop new cathode and anode materials with high capacities for sodium-ion batteries. Herein, we report the synthesis of β-MnO2 nanorods with exposed tunnel structures by a hydrothermal method. The as-prepared β-MnO2 nanorods have exposed {111} crystal planes with a high density of (1 × 1) tunnels, which leads to facile sodium ion (Na-ion) insertion and extraction. When applied as cathode materials in sodium-ion batteries, β-MnO2 nanorods exhibited good electrochemical performance with a high initial Na-ion storage capacity of 350 mAh g-1. β-MnO2 nanorods also demonstrated a satisfactory high-rate capability as cathode materials for sodium-ion batteries.


Su D.,The Clean Tech Center | Kim H.-S.,Korea Electrotechnology Research Institute | Kim W.-S.,Daejung Energy Materials Co. | Wang G.,The Clean Tech Center
Chemistry - A European Journal | Year: 2012

Mesoporous nickel oxide nanowires were synthesized by a hydrothermal reaction and subsequent annealing at 400 °C. The porous one-dimensional nanostructures were analysed by field-emission SEM, high-resolution TEM and N 2 adsorption/desorption isotherm measurements. When applied as the anode material in lithium-ion batteries, the as-prepared mesoporous nickel oxide nanowires demonstrated outstanding electrochemical performance with high lithium storage capacity, satisfactory cyclability and an excellent rate capacity. They also exhibited a high specific capacitance of 348 F g -1 as electrodes in supercapacitors. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Su D.,The Clean Tech Center | Ahn H.-J.,Gyeongsang National University | Wang G.,The Clean Tech Center
Chemical Communications | Year: 2013

An in situ hydrothermal synthesis approach has been developed to prepare SnO2@graphene nanocomposites. The nanocomposites exhibited a high reversible sodium storage capacity of above 700 mA h g-1 and excellent cyclability for Na-ion batteries. In particular, they also demonstrated a good high rate capability for reversible sodium storage. © 2013 The Royal Society of Chemistry.


Sun B.,The Clean Tech Center | Liu H.,The Clean Tech Center | Munroe P.,University of New South Wales | Ahn H.,Gyeongsang National University | Wang G.,The Clean Tech Center
Nano Research | Year: 2012

A nanocomposite of CoO and a mesoporous carbon (CMK-3) has been studied as a cathode catalyst for lithium-oxygen batteries in alkyl carbonate electrolytes. The morphology and structure of the as-prepared nanocomposite were characterized by field emission scanning electron microscopy, transmission electron microscopy and high resolution transmission electron microscopy. The electrochemical properties of the mesoporous CoO/CMK-3 nanocomposite as a cathode catalyst in lithium-oxygen batteries were studied using galvanostatic charge-discharge methods. The reaction products on the cathode were analyzed by Fourier transform infrared spectroscopy. The CoO/CMK-3 nanocomposite exhibited better capacity retention than bare mesoporous CMK-3 carbon, Super-P carbon or CoO/Super-P nanocomposite. The synergistic effects arising from the combination of CoO nanoparticles and the mesoporous carbon nanoarchitecture may be responsible for the optimum catalytic performance in lithium-oxygen batteries. © 2012 Tsinghua University Press and Springer-Verlag Berlin Heidelberg.

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