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Biphasic silicon oxide nanocomposites as high-performance lithium storage materials
Park, Eunjun,Kim, Yeong Eun,Song, Juhye,Park, Min-Sik,Kim, Hansu The Royal Society of Chemistry 2019 Journal of materials chemistry. A, Materials for e Vol.7 No.26
<P>Silicon oxides (SiOx) have been widely explored as high-capacity lithium storage materials for lithium ion batteries (LIBs) due to the enhanced stability of their cycling performance compared to other Si-based materials. However, these materials suffer from insufficient electrochemical performance and reliability for commercial use in LIBs. Since the electrochemical performance of SiOx relies on microstructures and chemical compositions, we propose a material layout design of a biphasic SiOx composite that can achieve synergy between two different types of SiOx materials to improve electrochemical performance. Taking advantage of the properties of each component, a biphasic SiOx composite composed of silicon monoxide (SiO) and Si nanocrystals embedded in SiOx (Si/SiOx) exhibits notably improved electrochemical performance and suppressed volume expansion during cycling. The proposed biphasic material exhibits a high reversible capacity of 966 mA h g<SUP>−1</SUP> with excellent long-term cycle performance for up to 350 cycles. With a core-shell structure, the biphasic Si/SiOx-SiO composite also has excellent dimensional stability. This approach presents a promising way to produce highly reliable high-capacity anode materials with a low production cost for mass production.</P>
Hansu Park,Na-Yeon Ko,JeongEun Kim,Thomas Opel,Sebastian Wetterich,Alexander Fedorov,Anderei Shepelev,Jinho Ahn 대한지질학회 2021 대한지질학회 학술대회 Vol.2021 No.10
The Batagay megaslump (Yana Uplands, Northeast Siberia) exposes Pleistocene and Holocene permafrost layers with two massive ice complexes. Previous studies suggest that the ages of these ice layers as MIS4-2 and MIS16 for the Upper and Lower Ice Complexes, respectively. In this study, we present gas concentrations in air bubbles occluded in the ice complexes. We extracted gas by both wet and dry extraction methods and using gas chromatography system to analyze dry molar mixing ratios. CO₂, N₂O, and CH₄ concentrations cover large ranges. We observe CO₂ concentrations of 1.9-10.3%, N₂O of 0.1-8 ppm, and CH₄ of 30-170 ppm for the Lower Ice Complex, while CO₂ of 0.03-8.89%, N₂O of 0.3-70 ppm, and CH₄ of 5-980 ppm for the Upper Ice Complex. The N₂O concentration in the Upper Ice Complex is extraordinarily high compared with other permafrost regions. Also, the CH₄ and N₂O show a weak negative correlation in both ice complexes. The δ(N₂/Ar) values range from -8.06% to 33.86% for the Lower Ice Complex and -5.49% to 30.64% for the Upper Ice Complex. These values indicate that there is little melting during and after the ice complex formation, which is also supported by investigation of the bubble shapes. On the other hand, the δ(O₂/Ar) values range -89.01 to –67.43% and -98.07 to -47.06% for the Lower and Upper Ice Complexes, respectively. The highly depleted δ(O₂/Ar) values may indicate strong oxidation reactions by microbial activities and/or abiological oxidation reactions. Our future research with isotope analyses such as δ<SUP>15</SUP>N of N₂O and δ<SUP>13</SUP>C, <SUP>14</SUP>C of CO₂ may help us better constrain formation processes of the ice wedges and origin of the greenhouse gases. These studies will serve as a basis for studying the impact of global warming on permafrost.
Park, Hyeong-Il,Sohn, Myungbeom,Choi, Jeong-Hee,Park, Cheolho,Kim, Jae-Hun,Kim, Hansu Elsevier 2016 ELECTROCHIMICA ACTA Vol.210 No.-
<P><B>Abstract</B></P> <P>Melt-spun Si based alloy materials have gained much attention as high capacity anode materials for lithium-ion batteries because of their high capacity and relatively low production cost. However, their long-term cycle performance should be further improved for the commercial success. Herein, it is demonstrated that the electrochemical performances of Si/TiFeSi<SUB>2</SUB> active-inactive nanocomposite anode material could be further improved by the microstructural modification using its mechanical deformation. With the help of high-energy mechanical milling, the microstructural tuned Si/TiFeSi<SUB>2</SUB> nanocomposite material showed a reversible capacity of more than 1000mAhg<SUP>−1</SUP> with stable capacity retention up to 100 cycles. <I>Ex situ</I> X-ray diffraction analysis coupled with potentiostatic intermittent titration technique revealed that refining the sizes of the active Si and inactive TiFeSi<SUB>2</SUB> limited the lithiation of Si phase to Li<SUB>21</SUB>Si<SUB>8</SUB> and this suppressed lithiation led to less volume changes of the electrodes and the improvement of the mechanical integrity of Si/TiFeSi<SUB>2</SUB> nanocomposite material.</P>
Park, Min-Sik,Park, Eunjun,Lee, Jaewoo,Jeong, Goojin,Kim, Ki Jae,Kim, Jung Ho,Kim, Young-Jun,Kim, Hansu American Chemical Society 2014 ACS APPLIED MATERIALS & INTERFACES Vol.6 No.12
<P>Si/SiO<SUB><I>x</I></SUB> composite materials have been explored for their commercial possibility as high-performance anode materials for lithium ion batteries, but suffer from the complexity of and limited synthetic routes for their preparation. In this study, Si/SiO<SUB><I>x</I></SUB> nanospheres were developed using a nontoxic and precious-metal-free preparation method based on hydrogen silsesquioxane obtained from sol–gel reaction of triethoxysilane. The resulting Si/SiO<SUB><I>x</I></SUB> nanospheres with a uniform carbon coating layer show excellent cycle performance and rate capability with high-dimensional stability. This approach based on a scalable sol–gel reaction enables not only the development of Si/SiO<SUB><I>x</I></SUB> with various nanostructured forms, but also reduced production cost for mass production of nanostructured Si/SiO<SUB><I>x</I></SUB>.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/aamick/2014/aamick.2014.6.issue-12/am5019429/production/images/medium/am-2014-019429_0005.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/am5019429'>ACS Electronic Supporting Info</A></P>
Genetic structure of Hermetia illucens implies a recent bottleneck
Hansu Choi,Nam-Yong Park,Sung-Kyung Moon,Eunjoo Choi,Kwangin Cho,Yonggu Lee,Young-cheol Choi,Sang-beom Lee,Gilsang Jeong 한국응용곤충학회 2010 한국응용곤충학회 학술대회논문집 Vol.2010 No.10
The black soldier fly (Hermetia illucens) (Diptera: Stratiomyidae) is an invasive species that is thought to be endemic in Korea. The insect has been paid much attention thanks to its ability to decompose organic wastes. We collected the insect nation-wide in 2006 and 2010 to investigate its genetic structure based on the mitochondrial cytochrome oxidase 1 (mt CO1) haplotype. The results show that during the time period the insect seems to lose some rare haplotypes. We conclude that the insect may have experienced genetic bottleneck while its settlement in Korea. In our presentation, we show its updated haplotype network and genetic differentiation and propose potential explanations.
Park, Gwi Ok,Yoon, Jeongbae,Park, Eunjun,Park, Su Bin,Kim, Hyunchul,Kim, Kyoung Ho,Jin, Xing,Shin, Tae Joo,Kim, Hansu,Yoon, Won-Sub,Kim, Ji Man American Chemical Society 2015 ACS NANO Vol.9 No.5
<P>To monitor dynamic volume changes of electrode materials during electrochemical lithium storage and removal process is of utmost importance for developing high performance lithium storage materials. We herein report an <I>in operando</I> probing of mesoscopic structural changes in ordered mesoporous electrode materials during cycling with synchrotron-based small angel X-ray scattering (SAXS) technique. <I>In operando</I> SAXS studies combined with electrochemical and other physical characterizations straightforwardly show how porous electrode materials underwent volume changes during the whole process of charge and discharge, with respect to their own reaction mechanism with lithium. This comprehensive information on the pore dynamics as well as volume changes of the electrode materials will not only be critical in further understanding of lithium ion storage reaction mechanism of materials, but also enable the innovative design of high performance nanostructured materials for next generation batteries.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/ancac3/2015/ancac3.2015.9.issue-5/acsnano.5b01378/production/images/medium/nn-2015-013783_0006.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nn5b01378'>ACS Electronic Supporting Info</A></P>
Park, Eunjun,Yoo, Hyundong,Lee, Jaewoo,Park, Min-Sik,Kim, Young-Jun,Kim, Hansu American Chemical Society 2015 ACS NANO Vol.9 No.7
<P>SiO<SUB><I>x</I></SUB>-based materials attracted a great deal of attention as high-capacity Li<SUP>+</SUP> storage materials for lithium-ion batteries due to their high reversible capacity and good cycle performance. However, these materials still suffer from low initial Coulombic efficiency as well as high production cost, which are associated with the complicated synthesis process. Here, we propose a dual-size Si nanocrystal-embedded SiO<SUB><I>x</I></SUB> nanocomposite as a high-capacity Li<SUP>+</SUP> storage material prepared <I>via</I> cost-effective sol–gel reaction of triethoxysilane with commercially available Si nanoparticles. In the proposed nanocomposite, dual-size Si nanocrystals are incorporated into the amorphous SiO<SUB><I>x</I></SUB> matrix, providing a high capacity (1914 mAh g<SUP>–1</SUP>) with a notably improved initial efficiency (73.6%) and stable cycle performance over 100 cycles. The highly robust electrochemical and mechanical properties of the dual-size Si nanocrystal-embedded SiO<SUB><I>x</I></SUB> nanocomposite presented here are mainly attributed to its peculiar nanoarchitecture. This study represents one of the most promising routes for advancing SiO<SUB><I>x</I></SUB>-based Li<SUP>+</SUP> storage materials for practical use.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/ancac3/2015/ancac3.2015.9.issue-7/acsnano.5b03166/production/images/medium/nn-2015-03166n_0006.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nn5b03166'>ACS Electronic Supporting Info</A></P>
Strategic design and fabrication of acrylic shape memory polymers
Park, Ju Hyuk,Kim, Hansu,Youn, Jae Ryoun,Song, Young Seok Institute of Physics Publishing 2017 Smart materials & structures Vol.26 No.8
<P>Modulation of thermomechanics nature is a critical issue for an optimized use of shape memory polymers (SMPs). In this study, a strategic approach was proposed to control the transition temperature of SMPs. Free radical vinyl polymerization was employed for tailoring and preparing acrylic SMPs. Transition temperatures of the shape memory tri-copolymers were tuned by changing the composition of monomers. X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy analyses were carried out to evaluate the chemical structures and compositions of the synthesized SMPs. The thermomechanical properties and shape memory performance of the SMPs were also examined by performing dynamic mechanical thermal analysis. Numerical simulation based on a finite element method provided consistent results with experimental cyclic shape memory tests of the specimens. Transient shape recovery tests were conducted and optical transparence of the samples was identified. We envision that the materials proposed in this study can help develop a new type of shape-memory devices in biomedical and aerospace engineering applications.</P>