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Sun B.,University of Technology, Sydney | Wang Y.,University of Technology, Sydney | Wang B.,University of Technology, Sydney | Kim H.-S.,Korea Electrotechnology Research Institute | And 2 more authors.
Journal of Nanoscience and Nanotechnology | Year: 2013

Porous LiFePO4/C microspheres were synthesized by a novel hydrothermal reaction combined with high-temperature calcinations. The morphology of the prepared material was investigated by fieldemission scanning electron microscopy. Porous microspheres with diameters around 1-3 μm were obtained, which consisting of primary LiFePO4 nanoparticles. The electrochemical performances of the as-prepared LiFePO4 microspheres were evaluated by cyclic voltammetry, electrochemical impedance spectroscopy and galvanostatic charge-discharge cycling. The carbon coated LiFePO4 microspheres showed lower polarization, higher rate capability, and better cycling stability than that of pristine LiFePO4 microspheres, indicating the potential application as the cathode material for high-power lithium ion batteries. Copyright © 2013 American Scientific Publishers.


Kim H.-J.,Korea Electrotechnology Research Institute | Jin B.-S.,Korea Electrotechnology Research Institute | Bae D.-S.,Changwon National University | Kim S.-B.,Daejung Energy Materials Co. | Kim H.-S.,Korea Electrotechnology Research Institute
Journal of Nanoscience and Nanotechnology | Year: 2013

LiMn0.6Fe0.4PO4/C cathode material is synthesized via a modified-solid state reaction method. The calcination temperature is adjusted in the range of 500-700 °C for 10 h. The crystal structure, morphology, and carbon coating layer of the synthesized LiMn 0.6Fe0.4PO4/C are analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM), respectively. The electrochemical performance of LiMn 0.6Fe0.4PO4/C, such as initial capacity, rate capability, cycling performance and EIS is also evaluated. The synthesized cathode material shows around 100~200 nm of primary particle size with no impurities. The highest initial discharge capacity of 162.1 mA h g-1 and columbic efficiency of 98.5% are obtained at a heat treatment temperature of 600 °C. In addition, LiMn0.6Fe0.4PO4/C active material shows the high capacity retention of 85% at 5 C compared to 0.2 C. It also shows the excellent capacity retention of 97.5% after the 50th charge/discharge. Copyright © 2013 American Scientific Publishers.


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
Microporous and Mesoporous Materials | Year: 2012

Tuneable porous α-Fe2O3 materials were prepared by using a selective etching method. The structure and morphology of the as-prepared porous hematites have been systematically characterised by X-ray diffraction, field emission scanning electron microscope, and transmission electron microscope. We found that the pore size and pore volume can be controlled by adjusting the etching time during the synthesis process. The porous hematites have been applied for gas sensing and lithium storage in lithium ion cells. The porous α-Fe2O3 materials demonstrated a reversible lithium storage capacity of 1269 mAh/g. When used as a sensing material in gas sensors, porous α-Fe2O3 exhibited a superior sensitivity towards toxic and flammable gases. © 2011 Elsevier Inc. All rights reserved.


Sun B.,University of Technology, Sydney | Horvat J.,University of Wollongong | Kim H.S.,Korea Electrotechnology Research Institute | Kim W.-S.,Daejung Energy Materials Co. | And 2 more authors.
Journal of Physical Chemistry C | Year: 2010

Mesoporous α-Fe2O3 materials were prepared in large quantity by the soft template synthesis method using the triblock copolymer surfactant F127 as the template. Nitrogen adsorption-desorption isothermal measurements and transmission electron microscope observation revealed that the as-prepared mesoporous α-Fe2O3 nanostructures have large mesopores in a wide size range of 5-30 nm. It has been found that the Morin transition depends on thermal history of mesoporous α-Fe2O3, which is driven by surface anisotropy. Superparamagnetic behavior of mesoporous α-Fe2O3 is also associated with surface spins with blocking temperature around 50 K. When applied as gas sensors, mesoporous α-Fe2O3 nanostructures exhibited high gas sensitivity toward acetic acid and ethanol gas. As anodes in lithium ion cells, mesoporous α-Fe2O 3 materials show a high specific capacity of 1360 mAh/g with excellent cycling stability and high rate capacity. © 2010 American Chemical Society.


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
Journal of Power Sources | Year: 2013

A series of PtxCoy (x:y = 4, 2, 1, and 0.5) alloy nanoparticles deposited on Vulcan XC-72 carbon was prepared through a chemical reduction method. The structures and morphologies of the as-prepared nanoparticles were characterized by X-ray diffraction, field emission scanning electron microscopy and transmission electron microscopy, which revealed the formation of Pt-Co alloys during the co-reduction process. PtxCo y alloy nanoparticles were applied as catalysts in lithium-air batteries. Through electrochemical testing, we found that the Pt based alloy nanocatalysts significantly increased the specific capacity of lithium-air batteries and the increase of Co content in PtxCoy alloy nanoparticles further enhanced the catalytic activity. This result illustrated that PtxCoy alloy nanoparticles could be used as an efficient catalyst material for lithium-air batteries with the feature of much reduced cost, but drastically increased catalytic activity. © 2012 Elsevier B.V. All rights reserved.

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