• Korean Journal of Materials Research
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• v.32 no.11
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• pp.474-480
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• 2022

Lithium-ion batteries (LIBs) are powerful energy storage devices with several advantages, including high energy density, large voltage window, high cycling stability, and eco-friendliness. However, demand for ultrafast charge/discharge performance is increasing, and many improvements are needed in the electrode which contains the carbon-based active material. Among LIB electrode components, the conductive additive plays an important role, connecting the active materials and enhancing charge transfer within the electrode. This impacts electrical and ionic conductivity, electrical resistance, and the density of the electrode. Therefore, to increase ultrafast cycling performance by enhancing the electrical conductivity and density of the electrode, we complexed Ketjen black and graphene and applied conductive agents. This electrode, with the composite conductive additives, exhibited high electrical conductivity (12.11 S/cm), excellent high-rate performance (28.6 mAh/g at current density of 3,000 mA/g), and great long-term cycling stability at high current density (88.7 % after 500 cycles at current density of 3,000 mA/g). This excellent high-rate performance with cycling stability is attributed to the increased electrical conductivity, due to the increased amount of graphene, which has high intrinsic electrical conductivity, and the high density of the electrode.

• Fashion & Textile Research Journal
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• v.17 no.2
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• pp.216-226
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• 2015

This study identifies factors of perceived risk of up-cycling fashion products and investigates perceived risk factors that influence consumers' trust, purchase intention, and recommendation intention towards upcycling fashion products. We also examine the relationship of trust, purchase intention, and recommendation intention for upcycling fashion products. A qualitative research method using a free narrative form and depth interview were used. The perceived risk from up-cycling fashion products generated 5 factor solutions: aesthetic risk, sanitary risk, social risk, performance risk, and economic risk. Next, 201 effective data were collected from a questionnaire survey and analyzed with SPSS 22.0. The results are summarized as follows. First, aesthetic risk and performance risk had a negative effect on products. Second, aesthetic risk and performance risk had negative influence on purchase intention for upcycling fashion products. Third, performance risk had a negative impact on recommendation intention for upcycling fashion products. Fourth, trust had positive effect on purchase intention and recommendation intention for upcycling fashion products. The results of the current study provides various theoretical and practical implications for marketers and retailers interested in up-cycling fashion products.

• Journal of Electrochemical Science and Technology
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• v.15 no.2
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• pp.253-260
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• 2024

Proton exchange membrane water electrolysis (PEMWE) is an efficient method for utilizing renewable energy sources such as wind and solar powers to produce green hydrogen. For PEMWE powered by renewable energy sources, its durability is a crucial factor in its performance since irregular and fluctuating characteristics of renewable energy sources, especially for wind power, can deteriorate the stability of PEMWE. Triangular voltage cycle is well able to simulate fluctuating wind power, but its effect on the durability has not been investigated extensively. In this study, the performance degradation of the PEMWE cell operated with the triangular voltage cycling was investigated at different ramping rates. The measured current responses during the cycling gradually decreased for both ramping rates, and I-V curve measurements before and after the cycling confirmed the degradation of the performances of PEMWE. For both measurements, the degradation rate was larger for 300 mV s^-1 than 30 mV s^-1, and they were determined as 0.36 and 1.26 mV h^-1 (at the current density of 2 A cm^-2) at the ramping rates of 30 and 300 mV s^-1, respectively. The comparison with other studies on triangular voltage cycling also indicate that an increase in the ramping rate accelerates the deterioration of the PEMWE performance. X-ray photoelectron spectroscopy and transmission electron microscopy results showed that the Ir catalyst was oxidized and did not dissolve during the voltage cycling. This study suggests that the ramping rate of the triangular voltage cycling is an important factor for the evaluation of the durability of PEMWE cells.

• Bulletin of the Korean Chemical Society
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• v.31 no.5
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• pp.1228-1232
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• 2010

The nanocomposites of polypyrrole (PPy) and multi-walled carbon nanotube (MWCNT) with different composition are synthesized by the chemical oxidative polymerization method. In these composites, the MWCNTs are uniformly coated by PPy with different thickness. The electrochemical properties of the composite electrodes are investigated by cyclic voltammetry, galvanostatic charge-discharge cycling and electrochemical impedance spectroscopy. The full cells assembled with the PPy/MWCNT composite electrodes deliver initial specific capacitances ranging from 146.3 to 167.2 F/g at 0.5 mA/$cm^2$ and exhibit stable cycling characteristics. The effect of content of MWCNT in the composite on cycling performance of the cells is also investigated.

• Journal of the Microelectronics and Packaging Society
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• v.22 no.1
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• pp.27-34
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• 2015

The correlation between crack propagation and localized recrystallization are compared in a series of cross section analyses on thermal cycled edgebond and underfilm material applied wafer level chip scale package (WLCSP) components with a baseline of no-material applied WLCSP components. The results show that the crack propagation distribution and recrystallization region correlation can explain potential degradation mechanisms and support the damage accumulation history in a more efficient way. Edgebond material applied components show a shift of damage accumulation to a more localized region, thus potentially accelerated the degradation during thermal cycling. Underfilm material applied components triggered more solder joints for a more wider distribution of damage accumulation resulting in a slightly improved thermal cycling performance compared to no-material applied components. Using an analysis on localized distribution of recrystallized areas inside the solder joint showed potential value as a new analytical approach.

• Bulletin of the Korean Chemical Society
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• v.35 no.11
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• pp.3331-3335
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• 2014

We examine the potential use of disordered mesoporous carbon as a functional additive for confining dissolved Li-polysulfides and improving the cycling performance of Li-S batteries. To promote a better understanding of the correlation between the total pore volume of disordered mesoporous carbon and the cycling performance of Li-S batteries, a series of disordered mesoporous carbons with different total pore volumes are successfully synthesized using a commercial silica template. Based on the electrochemical and structural analyses, we suggest that the total pore volume of disordered mesoporous carbon is a predominant factor in determining its capability for either the absorption or adsorption of Li-polysulfides, which is primarily responsible for enhancing the cycling performance. The addition of disordered mesoporous carbon is also effective in enhancing the homogeneous distribution of active sulfur in the cathode, thereby affecting the cycling performance.

• Korean Journal of Materials Research
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• v.31 no.8
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• pp.458-464
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• 2021

Tungsten disulfide (WS₂), a typical 2D layerd structure, has received much attention as a pseudocapacitive material because of its high theoretical specific capacity and excellent ion diffusion kinetics. However, WS₂ has critical limits such as poor long-term cycling stability owing to its large volume expansion during cycling and low electrical conductivity. Therefore, to increase the high-rate performance and cycling stability for pseudocapacitors, well-dispersed WS₂ nanoparticles embedded in carbon nanofibers (WS₂-CNFs), including mesopores and S-doping, are prepared by hydrothermal synthesis and sulfurizaiton. These unique nanocomposite electrodes exhibit a high specific capacity (159.6 F g^-1 at 10 mV s^-1), excellent high-rate performance (81.3 F g^-1 at 300 mV s^-1), and long-term cycling stability (55.9 % after 1,000 cycles at 100 mV s^-1). The increased specific capacity is attributed to well-dispersed WS₂ nanoparticles embedded in CNFs that the enlarge active area; the increased high-rate performance is contributed by reduced ion diffusion pathway due to mesoporous CNFs and improved electrical conductivity due to S-doped CNFs; the long-term cycling stability is attributed to the CNFs matrix including WS₂ nanoparticles, which effectively prevent large volume expansion.

• Fashion & Textile Research Journal
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• v.19 no.3
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• pp.320-330
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• 2017

People have recently became interested in eco-friendly cycling that attracted further attention as a sport activity. The number of high school cyclists has increased due to the popularity of cycling; however, high school cyclists have trouble choosing cycling suits because there is no professional cycling suit for high school cyclists in Korea. Therefore, it is necessary to develop a professional cycling suit for high school cyclists because sportswear for athletes is an important means to improve performance. This study suggests a standard sizing system for high school student athletes' cycle tights. The subjects were 111 high school cyclists. The 3 clusters were categorized by cluster analysis, and the sizing system was classified according to three lower body types. The size intervals of waist girth, hip girth and height were 5cm, respectively. The most frequent sizes were 75-100-175 in figure type 1, 70-90-170 and 75-95-170 in figure type 2, 70-90-175 and 70-90-180 in figure type 3. The sizing system, which had frequencies more than 3.6%, was classified into 9 cases, 8 cases, and 5 cases, respectively by lower body types. The results will contribute to the development of athletic performance cycle wear for high school cyclists.

• Journal of Hydrogen and New Energy
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• v.20 no.4
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• pp.317-322
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• 2009

To investigate degradation mechanism of PEMFC operated with repetitive startup/shutdown cycling, i-V characteristics, impedance, cyclic voltamograms were measured. OCV decreased from 0.967 to 0.951 V while the cell voltage at 800mA/$cm^2$ from 0.657 to 0.563V, implying that the electrodes rather than membrane electrolyte was damaged during the cycling operation. Electrochemical analyses supported that the performance degradation could be mainly attributed to degradation of the electrodes such as a decrease in electrochemical active surface area rather than degradation of membrane.

• Bulletin of the Korean Chemical Society
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• v.31 no.11
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• pp.3190-3194
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• 2010

Mixed electrolytes formed by the combination of 1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl) imide (BMP-TFSI) ionic liquid and standard liquid electrolyte are prepared and characterized. Linear sweep voltammetry measurements demonstrate that these mixed systems exhibit a wide electrochemical stability window, allowing them to be suitable electrolyte for carbonaceous anode-based lithium-ion batteries. Lithium-ion cells composed of graphite anode and $LiCoO_2$ cathode are assembled using the mixed electrolytes, and their cycling performances are evaluated. The cell containing proper content of BMP-TFSI shows good cycling performance comparable to that of a cell assembled with organic electrolyte. The presence of BMP-TFSI in the mixed electrolyte contributes to the reduction of the flammability of electrolyte solution and the improvement of the thermal stability of charged $Li_{1-x}CoO_2$ in the electrolyte solution.