• Clean Technology
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• v.19 no.1
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• pp.44-50
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• 2013

Tin-based materials for lithium ion battery have been proposed as new anode candidates owing to their higher specific capacity and relatively high lithium insertion potential. Tin-based materials have been extensively studied as possible replacements for carbon anodes in lithium ion batteries. However, the large volume expansion results in severe particle cracking with loss of electrical contact, giving irreversible capacity losses which prevent the widespread use of tin-based materials in lithium batteries. So remaining studies of tin-based materials are alleviating volume expansion and improving cycle performance. In this work, $SnO_2-SiO_2$ composites were manufactured with sol-gel method to overcome their volume expansion. Carbon was coated with 10 vol% propylene gas. The characteristics of active material and the effect of heat treatment were investigated with TG/DTA, XRD, SEM and FT-IR. Electrochemical characteristics of these composites were measured with CR2032 type coin cells. Carbon coated $SnO_2-SiO_2$at $300^{\circ}C$ heat treatment showed the best electrochemical performance.

• Journal of the Institute of Electronics and Information Engineers
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• v.49 no.12
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• pp.89-94
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• 2012

In this paper, a UHF cavity-backed spiral antenna for partial discharge diagnosis is proposed. The proposed antenna consists of two-arm Archimedean spiral, a cavity, and a balun for feeding. The spiral antenna is designed for 0.3-1.5 GHz operating frequency. Two spiral arms of the proposed antenna are fed by a microstrip tapered-balun. In order to enhance the gain, the cavity is located in the back side of the spiral pattern. The proposed antenna is designed and simulated using CST Microwave Studio. The designed antenna is also fabricated and tested to validate performance. The measured radiation patterns are directional to the +z-axis and measured peak gain is 9.92 dBi.

• Korean Chemical Engineering Research
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• v.57 no.1
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• pp.5-10
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• 2019

In this study, electrochemical characteristics of artificial graphite coated with petroleum pitch using solvent method as anode material of lithium ion battery were investigated. As the solvent, n-hexane, toluene, tetrahydrofuran and quinoline were used. The surface of the prepared anode material was analyzed by SEM and TEM. Also the electrochemical performances of the prepared anode materials were performed by constant current first charge/discharge, cycle, cyclic voltammetry and impedance tests in the electrolyte of $LiPF_6$ dissolved inorganic solvents (EC:DEC=1:1 vol%). The coating thickness of the prepared graphite was about 100-500 nm and the graphite coated with THF solvent had a smoother surface than that using other solvents. It was found that pitch-coated graphite (THF) show the low initial irreversible capacity (51 mAh/g), the high discharge capacity (360 mAh/g) and coulombic efficiency (99%).

• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.6
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• pp.649-656
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• 2011

A model for the numerical simulation of lithium-ion batteries (LIBs) is developed for use in battery cell design, with a view to improving the performances of such batteries. The model uses Newman-type electrochemical and transfer $theories^{(1,2)}$ to describe the behavior of the lithium-ion cell, together with the Levenberg-Marquardt optimization scheme to estimate the performance or design parameters in nonlinear problems. The mathematical model can provide an insight into the mechanism of LIB behavior during the charging/discharging process, and can therefore help to predict cell performance. Furthermore, by means of least-squares fitting to experimental discharge curves measured at room temperature, we were able to obtain the values of transport and kinetic parameters that are usually difficult to measure. By comparing the calculated data with the life-test discharge curves (SB LiMotive cell), we found that the capacity fade is strongly dependent on the decrease in the reaction area of active materials in the anode and cathode, as well as on the electrolyte diffusivity.

• Journal of the Korean Electrochemical Society
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• v.12 no.2
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• pp.189-195
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• 2009

$\beta-Ga_{2}O_{3}$ nanorods were synthesized by chemical vapor deposition method using nickel-oxide nanoparticle as a catalyst and gallium metal powder as a source material. The average diameter of nanorods was around 160 nm and the average length was $4{\mu}m$. Also, we confirmed that the synthesis of nanorods follows the vapor-solid growth mechanism. From the results of X-ray diffraction and HR-TEM observation, it can be found that the synthesized nanorods consisted of a typical core-shell structure with single-crystalline $\beta-Ga_{2}O_{3}$ core with a monoclinic crystal structure and an outer amorphous gallium oxide layer. Li/$\beta-Ga_{2}O_{3}$ nanorods cell delivered capacity of 867 mAh/g-$\beta-Ga_{2}O_{3}$ at first discharge. Although the Li/$\beta-Ga_{2}O_{3}$ nanorods cell showed low coulombic efficiency at first cycle, the cell exhibited stable cycle life property after fifth cycle.

• Clean Technology
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• v.24 no.4
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• pp.332-338
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• 2018

Currently graphite is used as an anode active material for lithium ion battery. However, since the maximum theoretical capacity of graphite is limited to $372mA\;h\;g^{-1}$, a new anode active material is required for the development of next generation high capacity and high energy density lithium ion battery. The maximum theoretical capacity of Si is $4200mA\;h\;g^{-1}$, which is about 10 times higher than the maximum theoretical capacity of graphite. However, since the volume expansion rate is almost 400%, the irreversible capacity increases as the cycle progresses and the discharge capacity relative to the charge is remarkably reduced. In order to solve these problems, it is possible to control the particle size of the Si anode active material to reduce the mechanical stress and the volume change of the reaction phase, thereby improving the cycle characteristics. Therefore, in order to minimize the decrease of the charge / discharge capacity according to the volume expansion rate of the Si particles, the improvement of the cycle characteristics was carried out by pulverizing Si by a dry method with excellent processing time and cost. In this paper, Si is controlled to nano size using vibrating mill and the physicochemical and electrochemical characteristics of the material are measured according to experimental variables.

• Proceedings of the KIEE Conference
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• 2004.07c
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• pp.1975-1978
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• 2004

We developed internal and external type sensor to measure ultra-high frequency (UHF) partial discharge (PD) in 170 kV gas-insulated switchgears (GIS). We also manufactured a PD-generator to verify and measure the detection sensitivity of those sensors. We measured the output power of the UHF PD sensors induced by PDs of 5 pC using the PD-generator. We measured UHF propagation loss of an 170 kV GIS for optimal arrangement of the sensors. We used swept UHF signal from a network analyzer into the GIS to measure the loss of various components of the GIS.

• Proceedings of the KIEE Conference
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• 2008.07a
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• pp.1378-1379
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• 2008

In this study, we developed intelligent spacer built in the internal type UHF PD sensors. 3-Dimensional electro-magnetic simulations were performed to analyze electric-field distribution of the single-phase GIS and three-phase GIS. After considering the spacer's specification, Sensor structures were designed and analyzed using the 3-D EM Simulator. As a result of the simulation the internal type UHF PD sensors were built in. Performance of the sensor built into real scale GIS spacer was measured in terms of return loss and detected Max voltage. And we identified a character of the intelligent spacer by using 5pC partial discharge cell.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.06a
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• pp.505-506
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• 2006

PD(partial discharge) occurred from variable PD sources in air may be the cause of breakdown in high voltage equipment which affect huge outage in power system. Identification and localization of PD sources is very important for engineer to cope with huge accident beforhand. PD phenomena can be detected by acoustic emission sensor or electromagnetic sensor like antenna. This paper has investigated the identification method using PCA(principal component analysis) for the PD signals from variable PD sources, for which the electric field distribution and PD inception voltages were simulated by using commercial FEM program. PD signals was detected by ultra wideband antenna. Their own features were extracted as the frequency coefficients transformed with FFT(fast fourier transform) and used to obtain independent pincipal components of each PD signals.

• Korean Chemical Engineering Research
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• v.51 no.4
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• pp.411-417
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• 2013

To use as an anode material of lithium secondary battery, graphite-silicon composite powders are prepared by ball-milling with silicon nanoparticles (average diameter 100 nm, 0~50 wt%) and graphite powder (average diameter $15{\mu}m$) and their electrochemical properties are examined. As the silicon content increases, the graphite becomes smaller by the ball-milling and amorphous phase appears whereas the silicon do not suffer the change of nanocrystalline phases and embeds within the amorphous phase of graphite. Cyclic voltammetry at low scan rate reveals that typical oxidation peaks of graphite and silicon appear at 0.2~0.35 and 0.55~0.6 V, respectively, with higher reversibility for repeated cycles. In contrast, the high-scan-rate redox behavior is very irreversible for repeated cycles. High irreversible capacity is exhibited in the initial charging-discharging cycles, but it diminishes as the cycle number increases. The saturated discharge capacity achieves about 485 mAh $g^{-1}$ at 50th cycle for the composite of Si 20 wt%. This is due to the formation of amorphous graphite morphology by the adequate composition (C:Si=8:2 w/w), which efficiently buffers the volume change during alloying/dealloying between silicon and lithium.