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A self-healing Sn anode with an ultra-long cycle life for sodium-ion batteries
Kim, Changhyeon,Kim, Icpyo,Kim, Huihun,Sadan, Milan K.,Yeo, Hyewon,Cho, Gyubong,Ahn, Jaepyoung,Ahn, Jouhyeon,Ahn, Hyojun The Royal Society of Chemistry 2018 Journal of Materials Chemistry A Vol.6 No.45
<P>For a next-generation sodium battery to replace lithium ion batteries, it is essential to develop an anode with a long cycle life and high rate. Sn is considered to be an ideal candidate for the anode of sodium ion batteries. Here, we report a Sn anode that exhibits ultra-long-term cycle stability with a high capacity of 554 mA h g<SUP>−1</SUP> at 10C-rate for 5000 cycles. The optimized cell configuration consists of 1,2-dimethoxyethane as the electrolyte, a double separator including a nanoporous membrane, and a Sn anode with MWCNT as a conductive additive. Its capacity retention reaches up to 99.8% and its coulombic efficiency is near 100% for 5000 cycles. Surprisingly, we have discovered that the Sn powder exhibits a self-healing phenomenon during cycling. Sn is initially pulverized into a nanometer-sized powder, and then forms a three-dimensional porous coral-like structure in which ligament-shaped micrometer-sized Sn particles are connected with a low coordination number by room temperature sintering. The coral-like structure is mechanically stable towards volume change and electrically connected. The self-healing structure and mechanism provide a direction for the design of other electrodes with alloying mechanisms.</P>
Kim Gyubong 한국물리학회 2022 Current Applied Physics Vol.38 No.-
The thermal expansion coefficients (α) of Fe1-xNix alloys are calculated by means of the Debye-Grüneisen model, which uses the input parameters calculated from density functional theory (DFT) with collinear spin alignments. The various atomic configurations of fcc and bcc supercells with x being 0–0.5 are calculated to conduct the composition-specific analysis. Thermodynamic analysis is employed to facilitate the evaluation of α in bulk alloys, where the calculated supercells are used as the canonical ensemble. Such calculated α exhibits very similar composition-dependency in comparison with the experimental data from literature, particularly providing the well-known Invar effect at 65 wt% of Fe. The calculations also demonstrated that the pressure-derived magnetic frustration, i.e. the magneto-volume effect, is strongly correlated with the Invar effect. The present approach combining the Debye-Grüneisen formalism and the collinear DFT calculation is shown to be a comprehensive theoretical framework for analysis on the thermal expansion properties in metal alloys.
Indirect-to-Direct Band Gap Transition of Si Nanosheets: Effect of Biaxial Strain
Kim, Byung-Hyun,Park, Mina,Kim, Gyubong,Hermansson, Kersti,Broqvist, Peter,Choi, Heon-Jin,Lee, Kwang-Ryeol American Chemical Society 2018 The Journal of Physical Chemistry Part C Vol.122 No.27
<P>The effect of biaxial strain on the band structure of two-dimensional silicon nanosheets (Si NSs) with (111), (110), and (001) exposed surfaces was investigated by means of density functional theory calculations. For all the considered Si NSs, an indirect-to-direct band gap transition occurs as the lateral dimensions of Si NSs increase; that is, increasing lateral biaxial strain from compressive to tensile always enhances the direct band gap characteristics. Further analysis revealed the mechanism of the transition which is caused by preferential shifts of the conduction band edge at a specific <I>k</I>-point because of their bond characteristics. Our results explain a photoluminescence result of the (111) Si NSs [U. Kim et al., <I>ACS Nano</I><B>2011</B>, <I>5</I>, 2176-2181] in terms of the plausible tensile strain imposed in the unoxidized inner layer by surface oxidation.</P> [FIG OMISSION]</BR>
Gyubong Kim,정성철,한영규 한국물리학회 2013 Current Applied Physics Vol.13 No.9
We studied adsorption of several molecules (CO, CO2, H2O, N2O, NO, NO2, and O2) on hexagonal boronnitride (h-BN) monolayers supported on transition metal (TM) surfaces, using density functional calculations. We observed that all the molecules bind very weakly on the pristine h-BN, with binding energiesin the range of 0.02e0.03 eV. Interestingly, however, when h-BN is supported on the TM surface,NO2 and O2 become strongly chemisorbed on h-BN, with binding energies of >1 eV, whereas othermolecules still physisorbed, with binding energies of w0.1 eV at most. The electron transfer from TM topz states of h-BN played a substantial role in such strong bindings of NO2 and O2 on h-BN, as thesemolecules possess unpaired electrons that can interact with pz states of h-BN. Such selective molecularbinding on h-BN/TM originates from the peculiar distribution of the spin-polarized highest occupied andlowest unoccupied molecular orbitals of NO2 and O2. Strong molecular adsorption and high selectivitywould make the h-BN/TM system possible for a variety of applications such as catalysts and gas sensors.
Kim, Byung-Hyun,Kim, Gyubong,Park, Kihoon,Shin, Mincheol,Chung, Yong-Chae,Lee, Kwang-Ryeol American Institute of Physics 2013 JOURNAL OF APPLIED PHYSICS - Vol.113 No.7
<P>A multi-scale approach connecting the atomistic process simulations to the device-level simulations has been applied to the Si(100)/SiO2 interface system. The oxidation of Si(100) surface was simulated by the atomic level molecular dynamics, the electronic structure of the resultant Si/suboxide/SiO2 interface was then obtained by the first-principles calculations, and finally, the leakage currents through the SiO2 gate dielectric were evaluated, with the obtained interface model, by the non-equilibrium Green's function method. We have found that the suboxide layers play a significant role for the electronic properties of the interface system and hence the leakage currents through the gate dielectric. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4791706]</P>
Carbon Monoxide-Tolerant Platinum Nanoparticle Catalysts on Defect-Engineered Graphene
Kim, Gyubong,Jhi, Seung-Hoon American Chemical Society 2011 ACS NANO Vol.5 No.2
<P>We studied catalytic performance, particularly tolerance against CO poisoning and particle migration, of Pt nanoparticles dispersed on graphene using <I>ab initio</I> calculations. It was shown that the binding of Pt nanoparticles to graphene and the molecular adsorption on Pt can be controlled by introducing defects on graphene. Pt d-band center is a key parameter that is tailored by such defect formation. It is observed that the binding energy difference between H<SUB>2</SUB> and CO is well correlated with the d-band center, whereas individual H<SUB>2</SUB> and CO binding energies are not. Relative occupation ratio of H<SUB>2</SUB> on Pt in a CO environment showed that Pt nanoparticles can tolerate CO more than does bulk Pt when the particles are deposited on nitrogen-doped graphene.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/ancac3/2011/ancac3.2011.5.issue-2/nn1017395/production/images/medium/nn-2010-017395_0006.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nn1017395'>ACS Electronic Supporting Info</A></P>
Design of a Wideband UHF RFID Printed Tag Antenna Using the R2R Process
KIM, Uisheon,JUNG, Gyubong,CHOI, Jaehoon The Institute of Electronics, Information and Comm 2010 IEICE TRANSACTIONS ON COMMUNICATIONS - Vol.93 No.8
<P>This paper proposes a printed tag antenna for the universal ultra-high frequency (UHF) radio frequency identification (RFID) band (860-960MHz) using the R2R process. To widen impedance bandwidth, a <I>π</I>-shaped matching network is suggested. The overall dimension of the proposed tag antenna is 83.4mm × 30.2mm and it has a gain of over 1dBi for the entire UHF RFID band. The performances of the proposed tag antenna, printed with conductivity silver ink using an R2R process, are compared with those of a copper antenna.</P>