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Kim Kisuk,Kim Jaewon,Lee Changmu,Kim Joorak,Lee Hansang 대한전기학회 2021 Journal of Electrical Engineering & Technology Vol.16 No.4
This paper presents an PSO-based optimization methodology for estimating the capacities and initial SOC of an energy storage systems (ESSs) in a DC electric railway system. The proposed method calculates the optimal solution using the missing capacity caused by the limited storage capacity. The missing capacity can be estimated through continuous-powerfl ow analysis. In many previous studies, capacities was calculated by assuming the each ESS as an independent device. However, since each storage device aff ects the charging and discharging operation of each other, this assumption might aff ect the convergence characteristics. In this paper, to solve this problem, the missing capacity of the ESS at both sides is refl ected by using the relating coeffi cient derived based on the electrical distance between storage devices. The case studies show that the most effi cient operation without missing capacity is possible under the derived capacities and initial SOC
Kim, Haegyeom,Kim, Hyungsub,Kim, Sung-Wook,Park, Kyu-Young,Kim, Jinsoo,Jeon, Seokwoo,Kang, Kisuk Elsevier 2012 Carbon Vol.50 No.5
<P><B>Abstract</B></P><P>LiFePO<SUB>4</SUB> nanoparticles were grown on nano-graphite platelet (NGP) using a simple chemical route. The material was used as the cathode in Li-ion rechargeable batteries and exhibited excellent cyclability and rate capability because of the easy electron transport in it. The electrochemical stability of the electrode was improved by the two-dimensional conductive network of the NGP. The resulting electrodes delivered a specific capacity of about 150mAhg<SUP>−1</SUP> at a current rate of 135mAg<SUP>−1</SUP> (∼0.8C) after 100 cycles with no capacity fade. At elevated current rates, the electrodes exhibited capacities of more than 100mAhg<SUP>−1</SUP> at a current density of 2000mAg<SUP>−1</SUP> (∼12C) without further incorporation of conductivity agents or coatings.</P>
Kim, Hyunchul,Park, Gwi Ok,Kim, Yunok,Muhammad, Shoaib,Yoo, Jaeseung,Balasubramanian, Mahalingam,Cho, Yong-Hun,Kim, Min-Gyu,Lee, Byungju,Kang, Kisuk,Kim, Hansu,Kim, Ji Man,Yoon, Won-Sub American Chemical Society 2014 Chemistry of materials Vol.26 No.22
<P>Tin oxide-based materials, operating via irreversible conversion and reversible alloying reaction, are promising lithium storage materials due to their higher capacity. Recent studies reported that nanostructured SnO<SUB>2</SUB> anode provides higher capacity beyond theoretical capacity based on the alloying reaction mechanism; however, their exact mechanism remains still unclear. Here, we report the detailed lithium storage mechanism of an ordered mesoporous SnO<SUB>2</SUB> electrode material. Synchrotron X-ray diffraction and absorption spectroscopy reveal that some portion of Li<SUB>2</SUB>O decomposes upon delithiation and the resulting oxygen reacts with Sn to form the SnO<SUB><I>x</I></SUB> phase along with dealloying of Li<SUB><I>x</I></SUB>Sn, which are the main reasons for unexpected high capacity of an ordered mesoporous SnO<SUB>2</SUB> material. This finding will not only be helpful in a more complete understanding of the reaction mechanism of Sn-based oxide anode materials but also will offer valuable guidance for developing new anode materials with abnormal high capacity for next generation rechargeable batteries.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/cmatex/2014/cmatex.2014.26.issue-22/cm5025603/production/images/medium/cm-2014-025603_0012.gif'></P>
UV-curing kinetics and performance development of <i>in situ</i> curable 3D printing materials
Kim, Ye Chan,Hong, Sungyong,Sun, Hanna,Kim, Myeong Gi,Choi, Kisuk,Cho, Jungkeun,Choi, Hyouk Ryeol,Koo, Ja Choon,Moon, Hyungpil,Byun, Doyoung,Kim, Kwang J.,Suhr, Jonghwan,Kim, Soo Hyun,Nam, Jae-Do Elsevier 2017 European polymer journal Vol.93 No.-
<P><B>Abstract</B></P> <P>As three-dimensional (3D) printing technology is emerging as an alternative way of manufacturing, the high resolution 3D printing device often requires systems such as drop jetting printing of <I>in situ</I> UV-curable photopolymers. Accordingly, the key issue is process control and its optimization to ensure dimensional accuracy, surface roughness, building orientation, and mechanical properties of printed structures, which are based on the time- and temperature-dependent glass transition temperature (<I>T<SUB>g</SUB> </I>) of the resin system under UV-curing. In this study, the UV-cure kinetics and <I>T<SUB>g</SUB> </I> development of a commercially available UV-curable acrylic resin system were investigated as a model system, using a differential scanning photocalorimeter (DPC). The developed kinetic model included the limited conversion of cure that could be achieved as a maximum at a specific isothermal curing temperature. Using the developed model, the <I>T<SUB>g</SUB> </I> was successfully described by a modified DiBenedetto equation as a function of UV curing. The developed kinetic model and <I>T<SUB>g</SUB> </I> development can be used to determine the 3D printing operating conditions for the overlay printing and <I>in situ</I> UV curing, which could ensure high-resolution and high-speed manufacturing with various UV-curing materials.</P> <P><B>Highlights</B></P> <P> <UL> <LI> UV-cure kinetic analysis were applied to a commercial Multi-jet 3D printing material. </LI> <LI> The developed kinetic model included the limited conversion of cure by temperature. </LI> <LI> The <I>T<SUB>g</SUB> </I> was described by a modified DiBenedetto equation as a function of UV curing. </LI> <LI> The developed kinetic model showed an excellent agreement to isothermal experiments. </LI> <LI> The overlay printing time for each isothermal temperature was determined. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Kim, Jungmo,Yoon, Gabin,Kim, Jin,Yoon, Hyewon,Baek, Jinwook,Lee, Joong Hee,Kang, Kisuk,Jeon, Seokwoo Elsevier 2018 Carbon Vol.139 No.-
<P><B>Abstract</B></P> <P>Demand for an effective strategy for exfoliating layered materials into flakes without perturbing their intrinsic structure is growing. Herein, we introduce an effective fabrication method of large-sized non-oxidized graphene flakes (NOGFs) as a representative example of a general strategy using spontaneous insertion of exfoliating medium into a layered material. We fabricated a ternary graphite intercalation compound (t-GIC) with stoichiometry of KC<SUB>24</SUB>(THF)<SUB>2</SUB>, and analyzed its morphology and electronic structure through experimental and computational approach. Interactions between the t-GIC and aprotic organic solvents with different polarities were investigated, where a unique swelling behavior was observed with dimethyl sulfoxide (DMSO). Based on the analysis of the phenomena, we demonstrate facile exfoliation of the t-GIC in polyvinyl pyrrolidone (PVP)-DMSO solution for fabrication of highly crystalline and large-sized NOGFs. The lateral size of the NOGFs ranges over 30 μm, while the 98% having thickness below 10 layers. The NOGF film exhibits supreme electrical conductivity of 3.36 × 10<SUP>5</SUP> S/m, which is, to our best knowledge, the highest value for a thin conductive film made of graphene flakes.</P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
LiFePO<sub>4</sub> with an alluaudite crystal structure for lithium ion batteries
Kim, Jongsoon,Kim, Hyungsub,Park, Inchul,Park, Young-Uk,Yoo, Jung-Keun,Park, Kyu-Young,Lee, Seongsu,Kang, Kisuk The Royal Society of Chemistry 2013 Energy & environmental science Vol.6 No.3
<P>A novel Na-pillared LiFePO<SUB>4</SUB> with an alluaudite structure is reported and its structure is investigated. The alluaudite-LiFePO<SUB>4</SUB> allowed fast lithium diffusion with stable electrochemical cycling in lithium batteries. ∼0.8 Li<SUP>+</SUP> could be extracted and reinserted reversibly for extended cycles <I>via</I> one-phase reaction in contrast to the well-known two-phase reaction in olivine-LiFePO<SUB>4</SUB>.</P> <P>Graphic Abstract</P><P>The novel alluaudite-LiFePO<SUB>4</SUB> allows fast lithium diffusion with stable electrochemical cycling as a cathode in lithium batteries. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c3ee24393a'> </P>
Phase Stability Study of Li[sub 1−x]MnPO[sub 4] (0≤x≤1) Cathode for Li Rechargeable Battery
Kim, Sung-Wook,Kim, Jongsoon,Gwon, Hyeokjo,Kang, Kisuk The Electrochemical Society 2009 Journal of the Electrochemical Society Vol.156 No.8
<P>The phase stability of Li1-xMnPO4 (0 <= x <= 1) is investigated in this study for different Li compositions and temperatures by high temperature X-ray diffraction and electron microscopy. The map of stable phases is determined at temperature ranges between room temperature and 410 degrees C. While pure LiMnPO4 phase is stable at high temperature, partial phase transformation of MnPO4 into Mn2P2O7 is observed in delithiated phases above 210 degrees C. Electron microscopy study also indicates the instability of the delithiated phase. The morphology of LiMnPO4 is severely damaged upon delithiation. The instability of the delithiated phase and the phase transformation into Mn2P2O7 may imply that safety concerns can be raised regarding the LiMnPO4 cathode, unlike its Fe counterpart.</P>