Structurally and Electronically Designed TiO₂N_<i>x</i> Nanofibers for Lithium Rechargeable Batteries

Kim, Jae-Geun,Shi, Dongqi,Kong, Ki-Jeong,Heo, Yoon-Uk,Kim, Jung Ho,Jo, Mi Ru,Lee, Yoon Cheol,Kang, Yong-Mook,Dou, Shi Xue American Chemical Society 2013 ACS APPLIED MATERIALS & INTERFACES Vol.5 No.3

<P>The morphology and electronic structure of metal oxides, including TiO<SUB>2</SUB> on the nanoscale, definitely determine their electronic or electrochemical properties, especially those relevant to application in energy devices. For this purpose, a concept for controlling the morphology and electrical conductivity in TiO<SUB>2</SUB>, based on tuning by electrospinning, is proposed. We found that the 1D TiO<SUB>2</SUB> nanofibers surprisingly gave higher cyclic retention than 0D nanopowder, and nitrogen doping in the form of TiO<SUB>2</SUB>N<SUB><I>x</I></SUB> also caused further improvement. This is due to higher conductivity and faster Li<SUP>+</SUP> diffusion, as confirmed by electrochemical impedance spectra. Our findings provide an effective and scalable solution for energy storage efficiency.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/aamick/2013/aamick.2013.5.issue-3/am302197y/production/images/medium/am-2012-02197y_0007.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/am302197y'>ACS Electronic Supporting Info</A></P>

Reduction-Free Synthesis of Carbon-Encapsulated SnO₂ Nanowires and Their Superiority in Electrochemical Performance

Park, Min-Sik,Kang, Yong-Mook,Dou, Shi-Xue,Liu, Hua-Kun American Chemical Society 2008 JOURNAL OF PHYSICAL CHEMISTRY C - Vol.112 No.30

Progress in MgB2 Superconductor Wires and Tapes

김정호,Hiroaki Kumakura,Matthew Rindflesich,Shi Xue Dou,황수민,주진호 한국초전도학회 2011 Progress in superconductivity Vol.12 No.2

We report on the progress that has been made in developing MgB2 superconducting wires and tapes for commercialization and research efforts. A number of techniques have been developed to overcome the obstacle posed by the poor critical current density (Jc) of pristine MgB2. Chemical doping has proved to be the effective way to modify and enhance the superconducting properties, such as the Jc and the irreversibility field (Birr). More than 100 different types of dopants have been investigated over the past 8 years. Among these, the most effective dopants have been identified to be SiC and malic acid (C4H6O5). The best results, viz. a Birr of 22 T and Jc of 30,000 A·cm-2 at 4.2 K and 10 T, were reported for malic acid doped MgB2 wires, which matched the benchmark performance of commercial low temperature superconductor wires. In this work, we discuss the progress made in MgB2 conductors over the past few years at the University of Wollongong, Hyper Tech Research, Inc., and Ohio State University.

Effect of water partial pressure on the texture and the morphology of MOD-YBCO films on buffered metal tapes

정국채,유재무,고재웅,김영국,Xiaolin Wang,Shi Xue Dou 한국초전도.저온공학회 2007 한국초전도저온공학회논문지 Vol.9 No.2

The influence of water partial pressure inMetal-organic Deposition (MOD) method was investigated on the texture and the morphology of YBa2Cu3O7-X (YBCO) films grown on the buffered metal tapes. The water partial pressure was varied from 4.2% up to 10.0% with the other partial pressure, kept constant. In this work, the fluorine-free Y & Cu precursor solution added with Sm was synthesized and coated by the continuous slot-die coating & calcination step. The next annealing step of the YBCO films was done by the reel-to-reel method with the gas flowed vertically down. From the x-ray diffraction analysis, the un-reacted phase like BaF2 peak was found at the water partial pressure of 4.2%, but BaF2 peak intensity is much reduced as the water partial pressure is increased. However, the higher water partial pressure of about 10% in this experiment leads to the poor crystallinity of YBCO films. The morphologies of the YBCO films were not different from each other when the water partial pressure was varied in this work. The maximum 2 was obtained at the water partial pressure of 6.2% with the annealing temperature of 780oC and oxygen partial pressure of 500ppm.

Progress in $MgB_2$ Superconductor Wires and Tapes

Kim, Jung-Ho,Kumakura, Hiroaki,Rindflesich, Matthew,Dou, Shi Xue,Hwang, Soo-Min,Joo, Jin-Ho The Korean Superconductivity Society 2011 Progress in superconductivity Vol.12 No.2

We report on the progress that has been made in developing $MgB_2$ superconducting wires and tapes for commercialization and research efforts. A number of techniques have been developed to overcome the obstacle posed by the poor critical current density ($J_c$) of pristine $MgB_2$. Chemical doping has proved to be the effective way to modify and enhance the superconducting properties, such as the $J_c$ and the irreversibility field ($B_{irr}$). More than 100 different types of dopants have been investigated over the past 8 years. Among these, the most effective dopants have been identified to be SiC and malic acid ($C_4H_6O_5$). The best results, viz. a $B_{irr}$ of 22 T and $J_c$ of $30,000\;A{\cdot}cm^{-2}$ at 4.2 K and 10 T, were reported for malic acid doped $MgB_2$ wires, which matched the benchmark performance of commercial low temperature superconductor wires. In this work, we discuss the progress made in $MgB_2$ conductors over the past few years at the University of Wollongong, Hyper Tech Research, Inc., and Ohio State University.

Synthesis and Optimization of Fluorine-Free Y & Cu Precursor Solution for MOD Processing of YBCO Coated Conductor

Jaimoo Yoo,Young-Kuk Kim,Kookchae Chung,Jaewoong Ko,Xiaolin Wang,Shi Xue Dou Institute of Electrical and Electronics Engineers 2007 IEEE transactions on applied superconductivity Vol.17 No.2

<P>MOD solutions for YBCO coated conductors were synthesized with fluorine-free Y & Cu precursor. The fluorine content in the precursor solution was significantly reduced and a fast calcination profile was realized. A crack-free & thick precursor film was successfully obtained just after less than 2 hours of calcination in wet O<SUB>2</SUB> atmosphere. Optimization of the precursor solution with Sm addition enables further improvement of thickness and uniformity of precursor films. The calcinated precursor film was successfully converted to dense and uniform YBCO film after annealing in wet Ar/O<SUB>2</SUB> atmosphere. The measured critical current value was about 273 A/cm-w (J<SUB>c</SUB> ~ 3.8 MA/cm<SUP>2</SUP>), and well-developed microstructure was confirmed. Also discussed are recent developments in the reel-to-reel processing using the precursor solution with low fluorine-content. It was shown that employing fluorine-free Y & Cu precursor solution enabled uniform and fast processing of YBCO coated conductors.</P>

Sulfur–Graphene Nanostructured Cathodes <i>via</i> Ball-Milling for High-Performance Lithium–Sulfur Batteries

Xu, Jiantie,Shui, Jianglan,Wang, Jianli,Wang, Min,Liu, Hua-Kun,Dou, Shi Xue,Jeon, In-Yup,Seo, Jeong-Min,Baek, Jong-Beom,Dai, Liming American Chemical Society 2014 ACS NANO Vol.8 No.10

<P>Although much progress has been made to develop high-performance lithium–sulfur batteries (LSBs), the reported physical or chemical routes to sulfur cathode materials are often multistep/complex and even involve environmentally hazardous reagents, and hence are infeasible for mass production. Here, we report a simple ball-milling technique to combine both the physical and chemical routes into a one-step process for low-cost, scalable, and eco-friendly production of graphene nanoplatelets (GnPs) edge-functionalized with sulfur (S-GnPs) as highly efficient LSB cathode materials of practical significance. LSBs based on the S-GnP cathode materials, produced by ball-milling 70 wt % sulfur and 30 wt % graphite, delivered a high initial reversible capacity of 1265.3 mAh g<SUP>–1</SUP> at 0.1 C in the voltage range of 1.5–3.0 V with an excellent rate capability, followed by a high reversible capacity of 966.1 mAh g<SUP>–1</SUP> at 2 C with a low capacity decay rate of 0.099% per cycle over 500 cycles, outperformed the current state-of-the-art cathode materials for LSBs. The observed excellent electrochemical performance can be attributed to a 3D “sandwich-like” structure of S-GnPs with an enhanced ionic conductivity and lithium insertion/extraction capacity during the discharge–charge process. Furthermore, a low-cost porous carbon paper pyrolyzed from common filter paper was inserted between the 0.7S-0.3GnP electrode and porous polypropylene film separator to reduce/eliminate the dissolution of physically adsorbed polysulfide into the electrolyte and subsequent cross-deposition on the anode, leading to further improved capacity and cycling stability.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/ancac3/2014/ancac3.2014.8.issue-10/nn5047585/production/images/medium/nn-2014-047585_0007.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nn5047585'>ACS Electronic Supporting Info</A></P>

Robust FeCo nanoparticles embedded in a N-doped porous carbon framework for high oxygen conversion catalytic activity in alkaline and acidic media

Gao, Xuan-Wen,Yang, Junghoon,Song, Kyeongse,Luo, Wen-Bin,Dou, Shi-Xue,Kang, Yong-Mook The Royal Society of Chemistry 2018 Journal of Materials Chemistry A Vol.6 No.46

<P>FeCo alloy nanoparticles were nucleated onto graphitic carbon layers through the pyrolysis of polydopamine (PDA) sub-micrometer spheres to form a highly active electrocatalytic system that exhibits excellent oxygen conversion catalytic activity in both alkaline and acidic media. Owing to the strong metal chelation capability during the chemical modification and high sp<SUP>2</SUP>-dominant carbon yield of PDA, an abundance of non-precious-metal ions were easily trapped and absorbed into the PDA segments at room temperature by catechol and amine functional groups, followed by the <I>in situ</I> nucleation of FeCo alloy nanoparticles on graphitic carbon layers during the pyrolysis. The contents of graphitic nitrogen and pyridinic nitrogen were significantly increased by the presence of the non-precious-metal ions during carbonization as well, which is a result of the chelation effect of non-precious-metal atoms. Meanwhile, the FeCo nanoparticles (diameter < 5 nm) were protected by the multi-layer-graphene-like carbon layer from the harsh acid and uniformly anchored on graphitic carbon sub-microspheres, which can greatly improve the catalytic durability, particularly in acidic media. From the perspective of the whole catalytic system being used as an air electrode in rechargeable Zn-air batteries, the porous nitrogen-doped graphitic carbon framework was functionalised as a continuous conductive framework due to its catalytic activity towards high oxygen conversion and good electrical conductivity.</P>

Surface Engineering Strategies of Layered LiCoO₂Cathode Material to Realize High-Energy and High-Voltage Li-Ion Cells

Kalluri, Sujith,Yoon, Moonsu,Jo, Minki,Park, Suhyeon,Myeong, Seungjun,Kim, Junhyeok,Dou, Shi Xue,Guo, Zaiping,Cho, Jaephil Wiley Blackwell (John Wiley Sons) 2017 Advanced energy materials Vol.7 No.1

<P>Battery industries and research groups are further investigating LiCoO2 to unravel the capacity at high-voltages (>4.3 vs Li). The research trends are towards the surface modification of the LiCoO2 and stabilize it structurally and chemically. In this report, the recent progress in the surface-coating materials i.e., single-element, binary, and ternary hybrid-materials etc. and their coating methods are illustrated. Further, the importance of evaluating the surface-coated LiCoO2 in the Li-ion full-cell is highlighted with our recent results. Mg, P-coated LiCoO2 full-cells exhibit excellent thermal stability, high-temperature cycle and room-temperature rate capabilities with high energydensity of approximate to 1.4 W h cc(-1) at 10 C and 4.35 V. Besides, pouch-type full-cells with high-loading (18 mg cm(-2)) electrodes of layered-Li(Ni,Mn)O-2 -coated LiCoO2 not only deliver prolonged cycle-life at room and elevated-temperatures but also high energy-density of approximate to 2 W h cc(-1) after 100 cycles at 25 degrees C and 4.47 V (vs natural graphite). The post-mortem analyses and experimental results suggest enhanced electrochemical performances are attributed to the mechanistic behaviour of hybrid surface-coating layers that can mitigate undesirable side reactions and micro-crack formations on the surface of LiCoO2 at the adverse conditions. Hence, the surface-engineering of electrode materials could be a viable path to achieve the high-energy Li-ion cells for future applications.</P>

$C_4H_6O_5$ 도핑된 $MgB_2/Fe$ 선재의 임계특성에 대한 열처리 온도의 영향

전병혁,김정호,김찬중,Jun, Byung-Hyuk,Kim, Jung-Ho,Dou, Shi Xue,Kim, Chan-Joong 한국초전도학회 2007 Progress in superconductivity Vol.9 No.1

The effects of the heat-treatment temperature on the carbon (C) substitution amount, full width at half maximum (FWHM) value, critical temperature ($T_c$), critical current density ($J_c$) have been investigated for 10 wt % malic acid ($C_4H_6O_5$)-doped $MgB_2/Fe$ wires. All the samples were fabricated by the in-situ powder-in-tube (PIT) method and heat-treated within a temperature range of $650^{\circ}C$ to $1000^{\circ}C$. As the heat-treatment temperature increased, it seemed that the lattice distortion was increased by a more active C substitution into the boron sites from the malic acid addition. These increased electron scattering defects seemed to enhance the $J_c-H$ properties in spite of an improvement in the crystallinity, such as a decrease of the FWHM value and an increase of the $T_c$. Compared to the un-doped wire heat-treated at $650^{\circ}C$ for 30 min, the $J_c$ was enhanced by the C doping in a high-field regime. The wire heat-treated at $900^{\circ}C$ resulted in a higher magnetic $J_c$ of approximately $10^4\;A/cm^2$ at 5 K and 8 T.