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Jeon, Hyunkyu,Jin, So Yeon,Park, Won Ho,Lee, Hongkyung,Kim, Hee-Tak,Ryou, Myung-Hyun,Lee, Yong Min Elsevier 2016 ELECTROCHIMICA ACTA Vol.212 No.-
<P><B>Abstract</B></P> <P>To meet the high requirements of future lithium secondary batteries based on lithium metal anodes for large-scale applications, we develop a cost-effective and environmentally friendly water-based method to prepare inorganic/polymer composite coating layers on commercial hydrophobic polyolefin-based microporous separators. To this end, we utilize a plasma-treatment technique. After the plasma treatment, the surface of the polyethylene (PE) separators changes from hydrophobic to hydrophilic, and the pore structures of the separators widen. These changes improve the affinity of the PE separators for polar liquid electrolytes and their ionic conductivities compared to those of bare PE and other ceramic-coated control systems. The polar functional groups derived from plasma treatment interact with the hydroxyl groups of water-soluble polymeric binders in the ceramic (Al<SUB>2</SUB>O<SUB>3</SUB>) coating layers, thereby improving the adhesion strength between the PE substrate and the ceramic coating layer. This improvement impedes hydrophobic recovery phenomena. As a result, plasma-treated ceramic-coated separators (plasma CCSs) exhibit superior power capability and cycle performance (plasma CCS maintained 94.7% of the initial discharge capacity up to the 1000th cycle at C/2, whereas bare PE’s remained high only up to the 300th cycle) in unit cells based on lithium metal anodes.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Plasma treatment technique realizes a 100% water-based ceramic coating process. </LI> <LI> Plasma treatment enhances the adhesion properties of ceramic coating layer. </LI> <LI> Al<SUB>2</SUB>O<SUB>3</SUB> coating layers impedes hydrophobic recovery after plasma treatment. </LI> <LI> Plasma-treated Al<SUB>2</SUB>O<SUB>3</SUB> layers improves cycle performance and rate capabilities. </LI> </UL> </P>
Crosslinkable polyhedral silsesquioxane-based ceramic-coated separators for Li-ion batteries
Jeon, Hyunkyu,Roh, Youngjoon,Jin, Dahee,Ryou, Myung-Hyun,Jeong, Yong-Cheol,Lee, Yong Min THE KOREAN SOCIETY OF INDUSTRIAL AND ENGINEERING 2019 JOURNAL OF INDUSTRIAL AND ENGINEERING CHEMISTRY -S Vol.71 No.-
<P><B>Abstract</B></P> <P>Inorganic polyhedral oligomeric silsesquioxane with epoxy functional groups (ePOSS) is newly presented as a co-binder for the ceramic-coated separator (CCS) for safe Li-ion batteries. The ePOSS-incorporated coating layer significantly improved the dimensional stability of the CCS at 140°C and maintained the original form even after an ignition test. Although the permeability of the CCS was slightly decreased due to the crosslinked structure of the silsesquioxane coating layer, it showed high electrochemical stability up to 5V. Moreover, the improved liquid electrolyte wettability by ePOSS co-binder enhanced the ionic conductivity and showed 93% of cycle capacity at 0.5C rate in Li-ion batteries.</P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Yuseok Jeon,Jaejin Koo,Hyunkyu Kim 한국전자파학회JEES 2019 Journal of Electromagnetic Engineering and Science Vol.19 No.3
In this study, we propose an approach for the design and satisfy the requirements of the fabrication of a reliable and stable high-frequency downconverter for the millimeter-wave (Ka band) and detail the contents of the approach. We design and fabricate a stable downconverter with a low noise figure, flat gain characteristics, and multi-channel characteristics suitable for millimeter-wave bands. The method uses the chip-and-wire process for the assembly and operation of a bare MMIC device into the RF path. To compensate for the mismatch among the many components used in the module, W/G transition, an image rejection mixer, a switch, and an amplifier suitable for millimeter-wave frequency characteristics are designed and applied to the downconverter. To reject the spurious signals generated from the complex local oscillation signals, the downconverter is designed to not affect the RF path. In the Ka-band downconverter, the gain is measured from 41.89 dB to 42.83 dB at 33–35 GHz with flatness of about 0.94 dB. The measured value of the noise figure at CH1 is 4.936 dB with a maximum value in the 0.75–1.25 GHz intermediate frequency. The third intermodulation measurement result is 61.83 dBc under a -50 dBm input power and above gain, and the switching to select a channel takes about 622 μs.
Gong, Seokhyeon,Jeon, Hyunkyu,Lee, Hoogil,Ryou, Myung-Hyun,Lee, Yong Min American Chemical Society 2017 ACS APPLIED MATERIALS & INTERFACES Vol.9 No.21
<P>To improve the rate capability and safety of lithium-ion batteries (LIBs), we developed an integrated separator/electrode by gluing polyethylene (PE) separators and electrodes using a polymeric adhesive (poly(vinylidene fluoride), PVdF). To fabricate thin and uniform polymer coating layers on the substrate, we applied the polymer solution using a spray-coating technique. PVdF was chosen because of its superior mechanical properties and stable electrochemical properties within the voltage range of commercial LIBs. The integrated separator/electrode showed superior thermal stability compared to that of the control PE separators. Although PVdF coating layers partially blocked the porous structures of the PE separators, resulting in reduced ionic conductivity (control PE = 0.666 mS cm(-1), PVdF-coated PE = 0.617 mS cm(-1)), improved interfacial properties between the separators and the electrodes were obtained due to the intimate contact, and the rate capabilities of the LIBs based on integrated separators/electrodes showed 176.6% improvement at the 7 C rate (LIBs based on PVdF-coated and control PE maintained 48.4 and 27.4% of the initial discharge capacity, respectively).</P>
분위기 압력에 따른 커먼레일 시스템의 비증발 디젤 분무특성에 관한 실험적 연구
전충환(Chunghwan Jeon),정정훈(Jeonghoon Jeong),김현규(Hyunkyu Kim),송주헌(Juhun Song),장영준(Youngjune Jang),조승완(Seungwan Cho) 한국자동차공학회 2010 한국자동차공학회 부문종합 학술대회 Vol.2010 No.5
It is very important to understand the spray characteristics and fuel injection conditions in direct injection diesel engine because the emission gas compositions from diesel engines are related to spray formation processes. The objective of the papers is the characteristics of the macroscopic behaviour of diesel sprays. In this study, the characteristics of diesel spray has been studied using a shadowgraph and laser scattering. The spray characteristics such as spray tip penetration and spray cone angle studied at various injection pressure and ambient pressure.