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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.


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 | 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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