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태양광 발전설비 안정성 향상을 위한 바이패스 다이오드 지능형 냉각 시스템
고재환(Jaehwan Ko),김충일(Chungil Kim),이충근(Chung-Geun Lee),이득광(Deukgwang Lee),고명근(Myeong-Geun Ko),고석환(Suk-Whan Ko),송형준(Hyung-Jun Song) 대한전기학회 2021 전기학회논문지 Vol.70 No.12
A Bypass diode maintains the efficiency and stability of photovoltaic systems (PV) under partial shading. However, the bypass diode failure may cause damage and fire in the PV system because the generated current continuously flows through it. Thus, we suggest an intelligent cooling fan system for the bypass diode to ensure the stability of PV. The cooling system consisted of a k-type temperature sensor, electrically controlled fan and auto-control system. If the temperature of bypass diode (Tdiode) exceeds specific points owing to partial shading and/or its failure, the cooling system will automatically turn on the fan to prevent bypass diode from abnormal heating. The analysis of Tdiode indicates that the system effectively decreases it below the melting point of the junction box (177 ℃). The cooling system is adequate for PV under partal shading or with a damaged diode. Consequently, our suggested intelligent cooling system can contribute to the safe operation of PV.
Ko, Jaehwan,Yoon, Young Soo Elsevier 2019 CERAMICS INTERNATIONAL Vol.45 No.1
<P><B>Abstract</B></P> <P>The lithium metal battery has attracted considerable attention as the ultimate lithium secondary battery for high energy density. However, safety issues and battery performance deterioration due to the growth of lithium dendrites have hampered the practical use of lithium metal batteries. Recently, lithium fluoride has been considered as a lithium metal protective layer to solve this problem. In this review, firstly, the results of the studies on dendrites and SEI that have been carried out to date are reviewed. Secondly, the results of studies on lithium fluoride are divided into additive, artificial SEI, and other methods and the possibilities of their practical use are discussed. Finally, the significance and limitations of the lithium fluoride studies are summarized, and general conclusions and prospects for recommended research directions to accelerate the commercialization of lithium metal batteries are presented.</P>
Jaehwan Kwon,Dongwoo Ko,Yuri Seo 글로벌지식마케팅경영학회 2015 Global Fashion Management Conference Vol.2015 No.06
This study demonstrates how consumers’ implicit self-theory orientations (Entity vs. Incremental) relate to their perceptions of luxury brand appeals (Functional vs. Non-functional). Specifically, our experiments show that the entity theorists are likely to value the hedonic appeal of luxury brands, whereas incremental theorists value their functional appeal. The study provides useful insights for managers for designing advertising messages and their positioning strategies for luxury brands.
Recent Progress in Cathode Materials for Thermal Batteries
Ko, Jaehwan,Kang, Seung Ho,Cheong, Hae-Won,Yoon, Young Soo The Korean Ceramic Society 2019 한국세라믹학회지 Vol.56 No.3
Thermal batteries are reserve batteries with molten salts as an electrolyte, which activates at high temperature. Due to their excellent reliability, long shelf life, and mechanical robustness, thermal batteries are used in military applications. A high-performance cathode for thermal batteries should be considered in terms of its high capacity, high voltage, and high thermal stability. Research progress on cathode materials from the recent decade is reviewed in this article. The major directions of research were surface modification, compounding of existing materials, fabrication of thin film cathode, and development of new materials. In order to develop a high-performance cathode, a proper combination of these research directions is required while considering mass production and cost.
Thin cathode for thermal batteries using a tape-casting process
Ko, Jaehwan,Kim, In Yea,Jung, Hyun Min,Cheong, Haewon,Yoon, Young Soo Elsevier 2017 CERAMICS INTERNATIONAL Vol.43 No.7
<P><B>Abstract</B></P> <P>Thin cathodes for thermal batteries with good homogeneity and a reproducible thickness were prepared using a tape-casting process. A single cell fabricated with a 100µm thick cathode using tape-casting process exhibited a specific capacity of 1934.08As/g. In contrast, a single cell fabricated with a pellet type 500µm thick cathode demonstrated a specific capacity of 1000.25As/g. The thin cathode, which exhibited excellent utilization of the electrode material due to the optimal thickness from an electrochemical point of view, showed good mechanical strength and excellent electrochemical properties making it suitable for use in thermal batteries.</P>
Ko Jaehwan,Yoon Young Soo 한국세라믹학회 2023 한국세라믹학회지 Vol.60 No.4
All-solid-state lithium metal batteries have attracted considerable attention as the next-generation energy storage devices with high energy density and safety. This review focuses on the properties of interfaces between solid electrolytes and lithium electrodes, which are important for realizing all-solid-state lithium metal batteries. Various functional materials were used for modifying such interfaces, including amorphous oxide solid electrolytes, LiF, Al 2O3, and carbon-based materials. After reviewing literature works related to this topic, we concluded that optimizing the combinations of the various functional materials should be studied more actively. In addition, along with performance optimization of functional materials, the development of mass-production processes should be carried out in parallel.
Ko, Jaehwan,Yoon, Young Soo Elsevier 2019 THIN SOLID FILMS - Vol.673 No.-
<P><B>Abstract</B></P> <P>In this study, lithium fluoride (LiF) was deposited on lithium (Li) metal by thermal evaporation in order to reduce degradation of Li metal batteries caused by growth of Li dendrites. Li | Li symmetric cells were used to measure impedance changes, overvoltage after cycling at 1 mA/cm<SUP>2</SUP> and 1 mAh/cm<SUP>2</SUP>, and surface images after 100 cycles. In addition, the residual capacity and Coulombic efficiency after 0.5C charge/discharge cycling were confirmed using LiCoO<SUB>2</SUB>|Li cells. Based on electrochemical impedance spectroscopy measurements, Li | Li symmetric cells made of LiF-coated Li showed no impedance changes, even 12 h after fabrication. During the overvoltage test with Li | Li symmetric cells, the cell with a 300 nm thick LiF layer showed highest stability under repeated cycling. The surface of the 300 nm LiF-coated Li was relatively smooth and almost no abnormal growth of Li was observed. In the LiCoO<SUB>2</SUB>|Li cells, 200 nm and 300 nm LiF-coated cells showed the best performance in terms of residual capacity. The 300 nm LiF-coated Li cell exhibited close to 100% Coulombic efficiency and remained more stable than the bare Li cell.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Lithium fluoride was deposited by thermal evaporation for stable lithium anode. </LI> <LI> The symmetric cell with 300 nm thick lithium fluoride was the most stable. </LI> <LI> Lithium fluoride-coated surface was relatively smooth after cycling. </LI> <LI> The LiCoO<SUB>2</SUB> cell with 300 nm thick lithium fluoride showed the best performance. </LI> </UL> </P>
High durability conductive textile using MWCNT for motion sensing
Ko, Jaehwan,Jee, Seunghyun,Lee, Joo Hyeon,Kim, Sun Hee Elsevier 2018 Sensors and actuators. A Physical Vol.274 No.-
<P><B>Abstract</B></P> <P>A conductive textile was fabricated by vacuum-filtration using conductive ink prepared from multi-walled carbon nanotubes. The fabricated conductive textile was evaluated as its resistance varied while it was subjected to repeat stretching at strain rates of 0% to 20%. The textile samples showed resistance variations of less than ±3% after 10,000 cycles of stretching, and the pulse of the resistance variation at a strain rate of 0%–20% remained uniform during the stretching cycles. A motion-sensing glove fabricated with the conductive textile showed that the pulse of the oscilloscope changed accurately with movements of the fingers. These results show that the conductive textile prepared in this study can be applied to motion-sensing products.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A conductive textile was fabricated by vacuum-filtration of water-based MWCNTs ink. </LI> <LI> The conductive textile showed resistance variations of less than ±3% after 10,000 cycles of stretching. </LI> <LI> A motion-sensing glove fabricated with the textile showed that signal changed accurately with movements of the fingers. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>