Yongin si, South Korea
Yongin si, South Korea

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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.


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.


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.


Yersak T.A.,University of Colorado at Boulder | Son S.-B.,Seoul National University | Cho J.S.,MK Electronic | Suh S.-S.,Samsung | And 4 more authors.
Journal of the Electrochemical Society | Year: 2013

In this paper we demonstrate an all-solid-state Li-ion battery with a specific energy of 225 mWh g-1 based upon the combined mass of both the composite anode and cathode. To realize this full cell, we pair an iron sulfide and sulfur composite cathode with a Si-based anode. The anode active material is a Si-Ti-Ni alloy with good ionic and electronic conductivity that attains a stable specific capacity of 400 mAh g-1 based upon the total mass of the composite anode. To our knowledge, this is the highest stable Si-based all-solidstate anode specific capacity reported to date. To utilize both a lithium free anode and cathode, we adopt a pre-lithiation technique involving stabilized lithium metal powder. This is the first time that this technique has been demonstrated in an all-solid-state battery. © 2013 The Electrochemical Society. All rights reserved.


McCracken M.J.,University of Waterloo | Kim H.J.,University of Waterloo | Mayer M.,University of Waterloo | Persic J.,Microbonds | And 2 more authors.
2010 12th IEEE Intersociety Conference on Thermal and Thermomechanical Phenomena in Electronic Systems, ITherm 2010 | Year: 2010

Wire bond reliability testing typically consists of aging bonds in a high temperature environment for long time periods, removing samples at intervals to assess bond shear strength and characterize the bond cross sections. In this way, the degradation of the bond can be monitored at discrete time intervals, and it is determined whether the bond will be reliable under long term operation at lower temperatures. This process is labour and time consuming. An alternative process is reported using piezoresistive integrated CMOS microsensors located around test bond pads. The sensors are sensitive to radial compressive or tensile stresses occurring on the bond pad due to intermetallic formation, voiding, and crack formation at the bond interface. Two sets of identical test chips are bonded with optimized Au ball bonds and aged for 2000 h at 175°C. One set is connected to equipment which monitors signals from the stress sensors, along with the contact resistance of the bonds. The other set of chips is destructively tested by shear tests and cross sectioning. It is found that the stress sensors are capable of indicating which stage of intermetallic growth is currently being experienced, by relating the signal to the relative density of the intermetallic compounds (IMCs) which form during aging. The sensors can detect the consumption by IMCs of each Al layer in a multilayer pad, and can monitor the formation of AuAl2 which indicates an advanced stage of aging. Sensor signals combined with contact resistance measurements provide a valuable tool for preliminary reliability studies, and give real-time insight into microstructural changes. Drop in shear strength of a ball bond is detected by a change in the microsensor signal combined with a contact resistance increase. ©2010 IEEE.


McCracken M.J.,University of Waterloo | Koda Y.,University of Waterloo | Kim H.J.,University of Waterloo | Kim H.J.,Korea Institute of Machinery and Materials | And 4 more authors.
IEEE Transactions on Components, Packaging and Manufacturing Technology | Year: 2013

The application of an alternative method of bond monitoring during high-temperature aging is reported using a custom made test chip with piezoresistive integrated CMOS microsensors located around test bond pads. The sensor detects radial stresses originating from the bond pad and can resolve changes because of intermetallic compound (IMC) formation, voiding, or crack formation at the bond interface. Optimized Au ball bonds are aged for over 2000 h at 175{\circ}{\rm C}. It is found that stress sensors next to the bonds are capable of showing the stages of IMC growth, consumption of pad Al layers, and monitoring the formation of low-density and Al-rich IMC ({\rm AuAl}-{2}) which shows an advanced stage of aging. In particular, a first stress signal increase corresponds to the conversion of all Al above the diffusion barrier into IMCs. The second increase in stress signal after a period of stability corresponds to conversion of all Al below the barrier into IMCs. The IMC formation in these periods causes shear strength increase. After complete bond Al consumption, the bond, however, reaches maximum strength. As bond degradation starts, e.g., by lateral IMC formation, voiding, and oxide formation, as well as because of lateral pad Al transformation to IMC, the signal exhibits a strong decrease. The findings are corroborated by results obtained from classical methods such as interruptive or destructive testing including visual inspection, shear testing, cross sectioning, and by bond resistance monitoring. © 2013 IEEE.


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.


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.


Son S.-B.,Seoul National University | Yersak T.A.,University of Colorado at Boulder | Piper D.M.,University of Colorado at Boulder | Kim S.C.,Seoul National University | And 6 more authors.
Advanced Energy Materials | Year: 2014

Phase pure natural cubic-FeS2 (pyrite) was embedded in a stabilized polyacrylonitrile (PAN) matrix. The performance of the PAN-FeS2 composite cathode suggests that the problems related to the mobility of the electroactive species of FeS2 can be addressed without the need for a costly all-solid-state battery structure. By the 50th cycle, the PAN-FeS2 electrode delivers 470 mA-hr/g, or 64% of its initial discharge capacity with a Coulombic efficiency approaching 99.25%. The ortho-FeS2 (marcasite) is observed as a full charge product, which is a first for conventional liquid batteries and validates the results of previous all-solid-state FeS2 battery study.


Kang C.S.,Seoul National University | Son S.-B.,Seoul National University | Kim J.W.,University of Colorado at Boulder | Kim S.C.,Seoul National University | And 8 more authors.
Journal of Power Sources | Year: 2014

This study reports a direct observation on the crack behavior of lithiated Si wafer. Three different Si wafers with <100>, <110> and <111> axes are investigated, to compare the crack behaviors of different orientation Si wafers. Electrochemically induced cracks in each orientated wafer have dissimilar crack behaviors, because the initiations and propagations of cracks are strongly affected by their orientation and strain energy release rate. It is also found that triangular humps and cracks are formed in the (111) wafer, which are discovered for the first time by in this study. Considering that volume expansion, cracks, and pulverizations of Si are the main issues for the commercial use of Si for Li ion battery, this study provides important insight that is relevant to the design of advanced Si anode materials. © 2014 Elsevier B.V. All rights reserved.

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