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Yongin si, South Korea

Son S.-B.,Seoul National University | Roh H.,Seoul National University | Kang S.H.,Korea Atomic Energy Research Institute | Chung H.-S.,Samsung | And 5 more authors.
Gold Bulletin | Year: 2011

Inhomogeneous microtexture evolution during the cold drawing process usually results in lean, sway, or sweep failure. The 〈111〉 longitudinal fiber texture has higher stiffness than the 〈100〉 texture and its proportion and distribution in the cross-section are critical for the bonding stability of fine gold wire. We investigated the inhomogeneous microtexture evolution of gold wire that was cold drawn through an asymmetric diamond die. In this study, the distributions of the 〈111〉 and 〈100〉 textures in a 20 μm diameter fine gold wire are the variables and their effects on the bonding stability of the wire were estimated by electron backscattered diffraction (EBSD) and finite element method (FEM) simulations. The use of a focused ion beam apparatus enabled a high quality of band contrast of the EBSD to be achieved in the exact half cross-sectional area of the fine gold wire. The detailed three-dimensional FEM results show that the asymmetric distribution of the textures plays a crucial role in increasing the spatial displacement of the gold bonding wire. © The Author(s) 2011. Source

Son S.-B.,Seoul National University | Son S.-B.,University of Colorado at Boulder | Kim S.C.,Seoul National University | Kang C.S.,Seoul National University | And 8 more authors.
Advanced Energy Materials | Year: 2012

This paper reports a Si-Ti-Ni ternary alloy developed for commercial application as an anode material for lithium ion batteries. Our alloy exhibits a stable capacity above 900 mAh g - 1 after 50 cycles and a high coulombic effi ciency of up to 99.7% during cycling. To enable a highly reversible nano-Si anode, melt spinning is employed to embed nano-Si particles in a Ti 4 Ni 4 Si 7 matrix. The Ti 4 Ni 4 Si 7 matrix fulfi lls two important purposes. First, it reduces the maximum stress evolved in the nano-Si particles by applying a compressive stress to mechanically confi ne Si expansion during lithiation. And second, the Ti 4 Ni 4 Si 7 matrix is a good mixed conductor that isolates nano-Si from the liquid electrolyte, thus preventing parasitic reactions responsible for the formation of a solid electrolyte interphase. Given that a coulombic effi ciency above 99.5% is rarely reported for Si based anode materials, this alloy's performance suggests a promising new approach to engineering Si anode materials. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source

Son S.-B.,Seoul National University | Son S.-B.,University of Colorado at Boulder | Trevey J.E.,University of Colorado at Boulder | Roh H.,Seoul National University | And 11 more authors.
Advanced Energy Materials | Year: 2011

We report the direct observation of microstructural changes of Li xSi electrode with lithium insertion. HRTEM experiments confirm that lithiated amorphous silicon forms a shell around a core made up of the unlithiated silicon and that fully lithiated silicon contains a large number of pores of which concentration increases toward the center of the particle. Chemomechanical modeling is employed in order to explain this mechanical degradation resulting from stresses in the Li x Si particles with lithium insertion. Because lithiation-induced volume expansion and pulverization are the key mechanical effects that plague the performance and lifetime of high-capacity Si anodes in lithium-ion batteries, our observations and chemomechanical simulation provide important mechanistic insight for the design of advanced battery materials. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source

Son S.-B.,Seoul National University | Lee Y.K.,Seoul National University | Kang S.H.,Korea Atomic Energy Research Institute | Chung H.-S.,University of Pennsylvania | And 3 more authors.
Engineering Failure Analysis | Year: 2011

This study examined the effects of inclusions on the gold wire drawing stress using the Finite Element Method (FEM). Al2O3 and SUS304 are used as the model inclusion materials, which are frequently found on the fracture surfaces of drawn wire. The wire drawing stress showed a strong correlation with the size and yield stress of the inclusions. In the case of Al2O3, a larger diameter induced more drawing stress in the wire, whereas in case of SUS304, a larger diameter induced less drawing stress in wire. The difference was estimated quantitatively by comparing the amount of equivalent plastic strain (PEEQ) in the wire, which is the result of an interaction between the wire and inclusion. This result shows that the reason of difference in drawing stress variation is due to the yield stress of the inclusion. © 2011 Elsevier Ltd. Source

Lee K.J.,Korea Basic Science Institute | Lee K.J.,Seoul National University | Yu S.-H.,Korea Basic Science Institute | Yu S.-H.,Seoul National University | And 10 more authors.
Journal of Power Sources | Year: 2014

Nano-Si embedded Si7Ti4Ni4 is synthesized with the melt spinning method, which is facile, and applicable to mass-production. Si7Ti4Ni4, the buffer material, is electrochemically inactive toward lithium. Nevertheless, Si 7Ti4Ni4 has good electrical conductivity, in the order of 105 S m-1, which is more conductive than amorphous carbon that is usually used as a coating material for active material. Furthermore, the surrounding grain boundaries of Si7Ti 4Ni4 effectively relax volume expansion of Si. Therefore, it plays a critical role in maintaining the structure of electrode and the integrity of active materials. As a result, nano-Si embedded in Si 7Ti4Ni4 shows outstanding cycle performance over 50 cycles at 400 mA g-1, and it maintains 86% of its specific capacity at 3200 mA g-1, compared with that of 400 mA g-1. This indicates that nano-Si embedded in Si7Ti4Ni 4 can be a promising anode material for lithium ion batteries. © 2013 Elsevier B.V. All rights reserved. Source

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