Phase Dynamics on Conversion-Reaction-Based Tin-Doped Ferrite Anode for Next-Generation Lithium Batteries

Um, Ji Hyun,Palanisamy, Kowsalya,Jeong, Mihee,Kim, Hyunchul,Yoon, Won-Sub American Chemical Society 2019 ACS NANO Vol.13 No.5

<P>The conventional view of conversion reaction is based on the reversibility, returning to an initial material structure through reverse reaction at each cycle in cycle life, which impedes the complete understanding on a working mechanism upon a progression of cycles in conversion-reaction-based battery electrodes. Herein, a series of tin-doped ferrites (Fe<SUB>3-<I>x</I></SUB>Sn<SUB><I>x</I></SUB>O<SUB>4</SUB>, <I>x</I> = 0-0.36) are prepared and applied to a lithium-ion battery anode. By achieving the ideal reoxidation into SnO<SUB>2</SUB>, the Fe<SUB>2.76</SUB>Sn<SUB>0.24</SUB>O<SUB>4</SUB> composite anchored on reduced graphene oxide shows a high reversible capacity of 1428 mAh g<SUP>-1</SUP> at 200 mA g<SUP>-1</SUP> after 100 cycles, which is the best performance of Sn-based anode materials so far. Significantly, a newly formed γ-FeOOH phase after 100 cycles is identified from topological features through synchrotron X-ray absorption spectroscopy with electronic and atomic structural information, suggesting the phase transformation from magnetite to lepidocrocite upon cycling. Contrary to the conventional view, our work suggests a variable working mechanism in an iron-based composite with the dynamic phases from iron oxide to iron oxyhydroxide in the battery cycle life, based on the reactivity of metal nanoparticles formed during reaction toward the solid electrolyte interface layer.</P> [FIG OMISSION]</BR>

SnO₂-Coated 3D Etched Cu Foam for Lithium-ion Battery Anode

Um, Ji Hyun,Kim, Hyunwoo,Cho, Yong-Hun,Yoon, Won-Sub The Korean Electrochemical Society 2020 Journal of electrochemical science and technology Vol.11 No.1

SnO₂-based high-capacity anode materials are attractive candidate for the next-generation high-performance lithium-ion batteries since the theoretical capacity of SnO₂ can be ideally extended from 781 to 1494 mAh g^-1. Here 3D etched Cu foam is applied as a current collector for electron path and simultaneously a substrate for the SnO₂ coating, for developing an integrated electrode structure. We fabricate the 3D etched Cu foam through an auto-catalytic electroless plating method, and then coat the SnO₂ onto the self-supporting substrate through a simple sol-gel method. The catalytic dissolution of Cu metal makes secondary pores of both several micrometers and several tens of micrometers at the surface of Cu foam strut, besides main channel-like interconnected pores. Especially, the additional surface pores on etched Cu foam are intended for penetrating the individual strut of Cu foam, and thereby increasing the surface area for SnO₂ coating by using even the internal of Cu foam. The increased areal capacity with high structural integrity upon cycling is demonstrated in the SnO₂-coated 3D etched Cu foam. This study not only prepares the etched Cu foam using the spontaneous chemical reactions but also demonstrates the potential for electroless plating method about surface modification on various metal substrates.

Hierarchical micro-lamella-structured 3D porous copper current collector coated with tin for advanced lithium-ion batteries

Park, Hyeji,Um, Ji Hyun,Choi, Hyelim,Yoon, Won-Sub,Sung, Yung-Eun,Choe, Heeman Elsevier 2017 APPLIED SURFACE SCIENCE - Vol.399 No.-

<P><B>Abstract</B></P> <P>A Novel 3D porous Sn-Cu architecture is prepared as an anode material for use in an advanced lithium-ion battery. Micro-lamellar-structured 3D porous Cu foam, which is electroless-plated with Sn as an active material, is used as anode current collector. Compared to Sn-coated Cu foil, the 3D Sn-Cu foam exhibits superior Li-ion capacity and stable capacity retention, demonstrating the advantage of 3D porous architecture by preserving its structural integrity. In addition, the effect of heat-treatment after Sn plating is investigated. Sn/Sn<SUB>6</SUB>Cu<SUB>5</SUB> and SnO<SUB>2</SUB>/Cu<SUB>10</SUB>Sn<SUB>3</SUB> were formed on and in the 3D Sn-Cu foam under the heat-treatment at 150°C and 500°C, respectively. The development of Cu<SUB>10</SUB>Sn<SUB>3</SUB> in the 3D Sn-Cu foam heat-treated at 500°C can be a key factor for the enhanced cyclic stability because the Cu<SUB>10</SUB>Sn<SUB>3</SUB> inactively reacts with Li-ion and alleviates the volume expansion of SnO<SUB>2</SUB> as an inactive matrix.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Sn-Cu scaffold anode fabricated by freeze-casting and electroless plating. </LI> <LI> Sn-Cu scaffold architecture shows superior capacity and cyclic stability at high current density. </LI> <LI> Sn-Cu scaffold electrode is commercially promising. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Processing and characterization of titanium dioxide grown on titanium foam for potential use as Li-ion electrode

Choi, Hyelim,Park, Hyeji,Um, Ji Hyun,Yoon, Won-Sub,Choe, Heeman Elsevier BV * North-Holland 2017 Applied Surface Science Vol.411 No.-

<P><B>Abstract</B></P> <P>This study investigates the processing and potential application of Ti foams to the anode of lithium-ion batteries (LIBs). Ti foam is successfully synthesized using a water-based freeze-casting process, and anatase titanium dioxide (TiO<SUB>2</SUB>) is formed on the surface of the Ti foam for application to the anode of LIB. The metallic Ti foam acts as a current collector “platform” with increased surface area and the TiO<SUB>2</SUB> surface coating acts as an active anode material. Coin-cell test results show that the unique combination of the Ti foam and the TiO<SUB>2</SUB> coating anode has highly stable cycling properties and can thus be considered promising for use as an advanced anode for LIBs that require high safety and stability. It is anticipated that the use of the unique Ti-foam-based electrode design will not only be limited to LIBs but also will be applied to other energy and environmental areas as a catalyst or filter.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Successful formation of anatase TiO<SUB>2</SUB> on the surface of Ti foam. </LI> <LI> Successful application of TiO<SUB>2</SUB>/Ti foam anode to lithium ion battery. </LI> <LI> TiO<SUB>2</SUB>/Ti foam anode shows remarkably stable capacity retention. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Solvent-polarity-induced hematite (α-Fe₂O₃) nanostructures for lithium-ion battery and photoelectrochemical applications

Pawar, Rajendra C.,Um, Ji Hyun,Kang, Suhee,Yoon, Won-Sub,Choe, Heeman,Lee, Caroline S. Elsevier 2017 ELECTROCHIMICA ACTA Vol.245 No.-

<P><B>Abstract</B></P> <P>A range of morphology-controlled hematite superstructures, including two-dimensional sheet assembly, microspheres with a vein-like network, hollow urchin with tapered nanorods, and flowers with porous branch-like structures, were obtained from different solvents via the solvothermal approach. The results showed that the variation of the solvent from protic to aprotic facilitated morphological modifications, with the solvent playing a key role in determining the overall architecture of the oxide particles under different polar conditions. A porous microsphere grown from water solvent delivered a reversible capacity of 880mAhg<SUP>−1</SUP> over 60 cycles at 200mAg<SUP>−1</SUP> with good rate stability. Here, the bicontinuous nanoporous structure, with well-developed mesoporosity in the microsphere, reduced the severity of volume changes during the cycling process and stabilized passivation layer growth. The hematite nanostructure grown from water/dimethylformamide solvent exhibited the highest photocurrent density of 190μA/cm<SUP>−2</SUP> vs. Ag/AgCl, which was attributed to the rapid transport of charge carriers in the porous nanostructure. Thus, solvent-mediated synthesis can be used to prepare a range of hematite porous nanostructures for use as an anode in lithium-ion batteries and as a photoanode in photoelectrochemical cells, as well as for water splitting, gas sensors, and catalytic applications.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Solvent polarity induced α-Fe<SUB>2</SUB>O<SUB>3</SUB> nanostructures via solvothermal method. </LI> <LI> Polar aprotic/protic solvent controls growth kinetics. </LI> <LI> Excellent lithium ion storage and photoelectrochemical properties. </LI> <LI> Mesoporus structure improves the actives sites and performances. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>Cycle performance of the porous microsphere grown from H<SUB>2</SUB>O solvent at 200mAg<SUP>−1</SUP> compared to similar hematite structures from the literature with veins network (inset TEM image).</P> <P>[DISPLAY OMISSION]</P>

A Study of the Spirit of the God in the Old Testament

Um, Hyun Sub 루터대학교 출판부 2002 神學과 信仰 Vol.13 No.-

Biomass Waste, Coffee Grounds-derived Carbon for Lithium Storage

Um, Ji Hyun,Kim, Yunok,Ahn, Chi-Yeong,Kim, Jinsoo,Sung, Yung-Eun,Cho, Yong-Hun,Kim, Seung-Soo,Yoon, Won-Sub The Korean Electrochemical Society 2018 Journal of electrochemical science and technology Vol.9 No.3

Biomass waste-derived carbon is an attractive alternative with environmental benignity to obtain carbon material. In this study, we prepare carbon from coffee grounds as a biomass precursor using a simple, inexpensive, and environmentally friendly method through physical activation using only steam. The coffee-derived carbon, having a micropore-rich structure and a low extent of graphitization of disordered carbon, is developed and directly applied to lithium-ion battery anode material. Compared with the introduction of the Ketjenblack (KB) conducting agent (i.e., coffee-derived carbon with KB), the coffee-derived carbon itself achieves a reversible capacity of ~200 mAh/g (0.54 lithium per 6 carbons) at a current density of 100 mA/g after 100 cycles, along with excellent cycle stability. The origin of highly reversible lithium storage is attributed to the consistent diffusion-controlled intercalation/de-intercalation reaction in cycle life, which suggests that the bulk diffusion of lithium is favorable in the coffee-derived carbon itself, in the absence of a conducting agent. This study presents the preparation of carbon material through physical activation without the use of chemical activation agents and demonstrates an application of coffee-derived carbon in energy storage devices.

동북아시아에 있어서 "기(氣, Ch'i)" 개념 연구

엄현섭 루터대학교 출판부 2000 神學과 信仰 Vol.11 No.-

Quality characteristics of brownies according to the replacement ratio of safflower seed powder

Do Hyun Sim,In Jae Park,Hui Sub Um,Gyeong Mi Lee,Su-A Lee,Jung-Kue Shin 한국산업식품공학회 2023 학술대회 및 심포지엄 Vol.2023 No.04

In Vitro Selection of IpaH Specific Binding DNA Aptamers for the Early Detection of S. sonnei

Myung-Sub SONG,Hyun-Ju UM,Sang-Hee LEE,Kyeong-Ah LEE,Jiho MIN,Yang-Hoon KIM 한국생물공학회 2012 한국생물공학회 학술대회 Vol.2012 No.4