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Thermal Stability of ZnS Nanowires Studied by Using In-situ Heating X-ray Diffraction
Seul Cham Kim,김지우,정희석,김도현,오규환 한국물리학회 2009 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.55 No.3
The thermal stability of ZnS nanowires grown in a Au/Pd-mediated vapor-liquid-solid manner was studied by using an X-ray diffractrometer equipped with an in-situ heating system. Using an in-situ heating X-ray system, we monitored the structural degradation of ZnS nanowires in the temperature range from 25 ˚C to 900 ˚C. From the X-ray diffraction data recorded from 25 ˚C to 900 ˚C, the as-synthesized ZnS nanowires were identified to have a sphalerite structure at 250 C and that initial structure was preserved up to 400 ˚C. Above 500 ˚C, a distinct sphalerite structure degradation was revealed, which is related to the disappearance of the (111) and the (200) peaks. Through the extended temperature region up to 900 ˚C, we found continuous reduction of the (111) and the (200) peaks. Especially, a pure Zn peak showed up at 700 ˚C, which can be considered to be due to a partial phase decomposition of ZnS nanowires. Further, we employed electron microscopes to observe the morphological and the structural changes corresponding to the initial and the final states of ZnS nanowire products. The thermal stability of ZnS nanowires grown in a Au/Pd-mediated vapor-liquid-solid manner was studied by using an X-ray diffractrometer equipped with an in-situ heating system. Using an in-situ heating X-ray system, we monitored the structural degradation of ZnS nanowires in the temperature range from 25 ˚C to 900 ˚C. From the X-ray diffraction data recorded from 25 ˚C to 900 ˚C, the as-synthesized ZnS nanowires were identified to have a sphalerite structure at 250 C and that initial structure was preserved up to 400 ˚C. Above 500 ˚C, a distinct sphalerite structure degradation was revealed, which is related to the disappearance of the (111) and the (200) peaks. Through the extended temperature region up to 900 ˚C, we found continuous reduction of the (111) and the (200) peaks. Especially, a pure Zn peak showed up at 700 ˚C, which can be considered to be due to a partial phase decomposition of ZnS nanowires. Further, we employed electron microscopes to observe the morphological and the structural changes corresponding to the initial and the final states of ZnS nanowire products.
Kim, Kee-Bum,Dunlap, Nathan Arthur,Han, Sang Sub,Jeong, Je Jun,Kim, Seul Cham,Oh, Kyu Hwan,Lee, Se-Hee The Electrochemical Society 2018 Journal of the Electrochemical Society Vol.165 No.9
<P>This study demonstrates the application of Si/C composite fibers as anode materials for all-solid-state lithium-ion batteries. Using polyacrylonitrile as the carbon precursor, Si/C fibers were prepared through electrospinning and subsequent heat-treating processes. To investigate the correlation between fiber diameter and electrochemical performance, we prepared three electrodes (A, B, C), containing Si/C fibers with similar to 2 mu m, similar to 1 mu m and similar to 0.1 mu m diameters, respectively. Our results revealed that although the composition of all three electrodes was nearly the same, the Si/C fiber based electrodes exhibited better capacity retention when their fiber diameters were smaller. Normalized to the total mass of electrode composite, the solid-state half-cell prepared with the smallest diameter (similar to 0.1 mu m) Si/C fibers achieved a reversible specific capacity of similar to 700 mAh g(-1) (normalized to electrode mass) over 70 cycles. We believe that this report can serve as an informative approach toward the utilization of electrospun Si/C fibers as anode materials for all-solid-state lithium-ion batteries. (C) The Author(s) 2018. Published by ECS.</P>
β-Ga2O3 Nanowires and Nanobelts Synthesized by Using GaAs Powder Evaporation
정희석,Seul Cham Kim,Do Hyun Kim,Ji Woo Kim,권오정,Chan Park,Kyu Hwan Oh 한국물리학회 2009 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.55 No.1
We report the synthesis and characterization of β (monoclinic)-Ga2O3 nanowires and nanobelts prepared by using GaAs powder evaporation under a low vacuum condition (300Torr). As-grown β-Ga2O3 nanostructures were synthesized based on the well-known vapor-liquid-solid (VLS) mechanism by employing a Au thin film and vapor-solid (VS) reaction. Dense and uniform Ga2O3 nanowires with a diameter of 80 nm were synthesized at a higher temperature (~800℃), while various nanostructures including nanowires and nanobelts were found around 650℃. The crystalline structures and the chemical compositions of the as-synthesized β-Ga2O3 nanostructures were characterized through X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy dispersive X-ray spectrometry (EDS). We report the synthesis and characterization of β (monoclinic)-Ga2O3 nanowires and nanobelts prepared by using GaAs powder evaporation under a low vacuum condition (300Torr). As-grown β-Ga2O3 nanostructures were synthesized based on the well-known vapor-liquid-solid (VLS) mechanism by employing a Au thin film and vapor-solid (VS) reaction. Dense and uniform Ga2O3 nanowires with a diameter of 80 nm were synthesized at a higher temperature (~800℃), while various nanostructures including nanowires and nanobelts were found around 650℃. The crystalline structures and the chemical compositions of the as-synthesized β-Ga2O3 nanostructures were characterized through X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy dispersive X-ray spectrometry (EDS).
Lee, Ji-Hoon,Kim, Ji Woo,Kang, Ho-Young,Kim, Seul Cham,Han, Sang Sub,Oh, Kyu Hwan,Lee, Se-Hee,Joo, Young-Chang The Royal Society of Chemistry 2015 Journal of materials chemistry. A, Materials for e Vol.3 No.24
<▼1><P>By introducing the ZrOx layer coated using a novel sputtering, the electrochemical performance of Li(Ni1/3Co1/3Mn1/3)O2 under liquid and solid electrolyte was greatly improved.</P></▼1><▼2><P>To date, most coating layers for electrode materials for Li-ion batteries have been fabricated using the sol–gel method or atomic layer deposition (ALD), which involve complicated processing steps and limited candidates for coating materials. With an emphasis on solving these issues, herein, a new coating methodology based on a sputtering system was developed, and sputtered zirconium oxide was coated on Li(Ni1/3Co1/3Mn1/3)O2 (L333) cathode powders. The continuous movement of the cathode powders during the coating procedure and the high kinetic energy from the sputtering process resulted in a highly uniform coating layer with multiple structures exhibiting a concentration and valence state gradient of Zr, <I>i.e.</I>, surface (mainly Zr<SUP>4+</SUP>) and doped (mainly Zr<SUP>2+</SUP>) layers. The ZrOx-coated L333 powders exhibited an outstanding capacity retention (96.3% at the 200th cycle) and superior rate capability compared with the uncoated version in a coin cell with 1 M LiPF6 in EC : DEC liquid electrolyte. The ZrOx-coated L333 powders also exhibited an enhanced specific capacity in a solid state battery cell with a sulfide-based inorganic solid-state electrolyte. The improved electrochemical performance of ZrOx/L333 was attributed to the synergetic effect from the surface and doped layers: physical/chemical protection of the active material surface, enhancement of Li-ion diffusion kinetics, and stabilization of the interfaces.</P></▼2>
Chung, Hee-Suk,Jung, Yeonwoong,Kim, Seul Cham,Kim, Do Hyun,Oh, Kyu Hwan,Agarwal, Ritesh American Chemical Society 2009 NANO LETTERS Vol.9 No.6
<P>We report self-assembly of highly aligned GeTe nanowires epitaxially grown on octahedral GeTe microcrystals in two well-defined directions by using one-step vapor transport process. The epitaxial relationship of nanowires with underlying microcrystals along with the growth orientations of nanowires were investigated in detail by electron microscopy combined with atomic unit cell models. We demonstrate that maximizing atomic planar density to minimize energy of the exposed surfaces is the determining factor that governs the unique growth characteristics of micro/nanostructures that evolve from three-dimensional octahedral microcrystals to tetrahedral bases to finally one-dimensional nanowires. The crystallographic understanding of structuring of crystalline nanomaterials obtained from this study will be critical to understand, predict, and control the growth orientation of nanostructures in three-dimensions.</P>
Self-Contained Fragmentation and Interfacial Stability in Crude Micron-Silicon Anodes
Heist, Ashley,Piper, Daniela Molina,Evans, Tyler,Kim, Seul Cham,Han, Sang Sub,Oh, Kyu Hwan,Lee, Se-Hee The Electrochemical Society 2018 Journal of the Electrochemical Society Vol.165 No.2
<P>The full electrochemical utilization of a crude micron-silicon anode is enabled by a simple and scalable cyclized-polyacrylonitrile (cPAN) electrode architecture paired with an innovative room temperature ionic liquid (RTIL) electrolyte. Field emission scanning electron microscopy, transmission electron microscopy, and electron energy loss spectroscopy show that the resilient cPAN coating mechanically contains the cycling-induced expansion, contraction, and fragmentation of the oversized silicon particles while an electrochemically robust solid-electrolyte interphase (SEI) layer prevents the perpetuation of irreversible side reactions. Prolonged electrochemical cycling data demonstrates unprecedented performance in both half-cell and full-cell configurations. Implementation of the micron-silicon anode constitutes a significant development in the evolution of safe and commercially-viable high-performance lithium-ion batteries. (C) 2018 The Electrochemical Society.</P>
Face-Centered-Cubic Lithium Crystals Formed in Mesopores of Carbon Nanofiber Electrodes
Lee, Byoung-Sun,Seo, Jong-Hyun,Son, Seoung-Bum,Kim, Seul Cham,Choi, In-Suk,Ahn, Jae-Pyoung,Oh, Kyu Hwan,Lee, Se-Hee,Yu, Woong-Ryeol American Chemical Society 2013 ACS NANO Vol.7 No.7
<P>In the foreseeable future, there will be a sharp increase in the demand for flexible Li-ion batteries. One of the most important components of such batteries will be a freestanding electrode, because the traditional electrodes are easily damaged by repeated deformations. The mechanical sustainability of carbon-based freestanding electrodes subjected to repeated electrochemical reactions with Li ions is investigated <I>via</I> nanotensile tests of individual hollow carbon nanofibers (HCNFs). Surprisingly, the mechanical properties of such electrodes are improved by repeated electrochemical reactions with Li ions, which is contrary to the conventional wisdom that the mechanical sustainability of carbon-based electrodes should be degraded by repeated electrochemical reactions. Microscopic studies reveal a reinforcing mechanism behind this improvement, namely, that inserted Li ions form irreversible face-centered-cubic (FCC) crystals within HCNF cavities, which can reinforce the carbonaceous matrix as strong second-phase particles. These FCC Li crystals formed within the carbon matrix create tremendous potential for HCNFs as freestanding electrodes for flexible batteries, but they also contribute to the irreversible (and thus low) capacity of HCNFs.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/ancac3/2013/ancac3.2013.7.issue-7/nn4019625/production/images/medium/nn-2013-019625_0006.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nn4019625'>ACS Electronic Supporting Info</A></P>
Conformal Coatings of Cyclized-PAN for Mechanically Resilient Si nano-Composite Anodes
Piper, Daniela Molina,Yersak, Thomas A.,Son, Seoung-Bum,Kim, Seul Cham,Kang, Chan Soon,Oh, Kyu Hwan,Ban, Chunmei,Dillon, Anne C.,Lee, Se-Hee Wiley Blackwell (John Wiley Sons) 2013 ADVANCED ENERGY MATERIALS Vol.3 No.6