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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>
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
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, 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, Haegyeom,Kim, Sung-Wook,Hong, Jihyun,Park, Young-Uk,Kang, Kisuk Cambridge University Press (Materials Research Soc 2011 Journal of materials research Vol.26 No.20
<▼1><B>Abstract</B><P/></▼1><▼2><P>A Mn3O4/graphene hybrid material is fabricated using a facile and simple in-situ reduction process and shown to be a promising anode for lithium rechargeable batteries. The hybrid material retains a high capacity with a good cycle life of up to 990 mAh g<SUP>−1</SUP> after 30 cycles. The excellent electrochemical performance is attributable to the unique nanostructure of the hybrid material. Highly crystalline Mn3O4 particles (20-30 nm) are uniformly dispersed on graphene whose high electronic conductivity and high surface area provide a conductive percolating network throughout the electrode in the hybrid material. The conductive graphene networks enhance an electron transfer in the electrode and promote the electrochemical activity of the crystalline Mn3O4.</P></▼2>
Sodium intercalation chemistry in graphite
Kim, Haegyeom,Hong, Jihyun,Yoon, Gabin,Kim, Hyunchul,Park, Kyu-Young,Park, Min-Sik,Yoon, Won-Sub,Kang, Kisuk The Royal Society of Chemistry 2015 ENERGY AND ENVIRONMENTAL SCIENCE Vol.8 No.10
<P>The insertion of guest species in graphite is the key feature utilized in applications ranging from energy storage and liquid purification to the synthesis of graphene. Recently, it was discovered that solvated-Na-ion intercalation can occur in graphite even though the insertion of Na ions alone is thermodynamically impossible; this phenomenon enables graphite to function as a promising anode for Na-ion batteries. In an effort to understand this unusual behavior, we investigate the solvated-Na-ion intercalation mechanism using <I>in operando</I> X-ray diffraction analysis, electrochemical titration, real-time optical observation, and density functional theory (DFT) calculations. The ultrafast intercalation is demonstrated in real time using millimeter-sized highly ordered pyrolytic graphite, in which instantaneous insertion of solvated-Na-ions occurs (in less than 2 s). The formation of various stagings with solvated-Na-ions in graphite is observed and precisely quantified for the first time. The atomistic configuration of the solvated-Na-ions in graphite is proposed based on the experimental results and DFT calculations. The correlation between the properties of various solvents and the Na ion co-intercalation further suggests a strategy to tune the electrochemical performance of graphite electrodes in Na rechargeable batteries.</P> <P>Graphic Abstract</P><P>The solvated-Na-ion intercalation in graphite is investigated in terms of stoichiometry, staging structure, and solvated ion configuration using combined experimental and theoretical studies. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c5ee02051d'> </P>
Kim, Hyungsub,Lee, Seongsu,Park, Young-Uk,Kim, Haegyeom,Kim, Jongsoon,Jeon, Seokwoo,Kang, Kisuk American Chemical Society 2011 Chemistry of materials Vol.23 No.17
<P>Structural characterization of Li<SUB>2–<I>x</I></SUB>MP<SUB>2</SUB>O<SUB>7</SUB> (M = Fe, Co) was carried out using neutron diffraction (ND) and X-ray diffraction (XRD) analyses to elucidate structural information and structural changes during an electrochemical reaction. The crystal system and space group were determined to be monoclinic <I>P</I>2<SUB>1</SUB>/<I>c</I> for both materials with <I>a</I> = 11.0192 (4) Å, <I>b</I> = 9.7488 (3) Å, <I>c</I> = 9.8057 (4) Å, and β = 101.569 (3)° for Li<SUB>2–<I>x</I></SUB>FeP<SUB>2</SUB>O<SUB>7</SUB> and <I>a</I> = 10.9574 (3), <I>b</I> = 9.6921 (3), <I>c</I> = 9.7611 (3), and β = 101.776 (2)° for Li<SUB>2–<I>x</I></SUB>CoP<SUB>2</SUB>O<SUB>7</SUB>. XRD analysis revealed partial occupancy of iron and cobalt in the structures of Li<SUB>2–<I>x</I></SUB>FeP<SUB>2</SUB>O<SUB>7</SUB> and Li<SUB>2–<I>x</I></SUB>CoP<SUB>2</SUB>O<SUB>7</SUB>, respectively. Also, ND identified lithium positions and partial occupancies in five different Li sites of Li<SUB>2–<I>x</I></SUB>MP<SUB>2</SUB>O<SUB>7</SUB> (M = Fe, Co). Further ex situ XRD showed that the charging/discharging of Li<SUB>2–<I>x</I></SUB>FeP<SUB>2</SUB>O<SUB>7</SUB> occurred primarily via a two-phase reaction with a slight solid solution behavior. We also demonstrated for the first time that Li<SUB>2–<I>x</I></SUB>CoP<SUB>2</SUB>O<SUB>7</SUB> electrodes are electrochemically active, with a redox potential of ∼5 V (versus Li).</P><P>We report the detailed structural analysis of Li<SUB>2−<I>x</I></SUB>MP<SUB>2</SUB>O<SUB>7</SUB> (M = Fe, Co) by combined neutron diffraction and X-ray diffraction analyses. XRD analysis revealed the partial occupancies of iron and cobalt in Li<SUB>2−<I>x</I></SUB>MP<SUB>2</SUB>O<SUB>7</SUB>, and ND identified lithium positions and partial occupancies of four different Li sites in the complex crystal structure of Li<SUB>2−<I>x</I></SUB>MP<SUB>2</SUB>O<SUB>7</SUB>. Atomic sites and occupancies were determined by simultaneous Rietveld refinement against XRD and ND patterns, and ex situ XRD analysis revealed that charging/discharging of Li<SUB>2−<I>x</I></SUB>FeP<SUB>2</SUB>O<SUB>7</SUB> occurs primarily via a two-phase reaction. Also, the Li<SUB>2−<I>x</I></SUB>CoP<SUB>2</SUB>O<SUB>7</SUB> electrode is electrochemically active with a redox potential of ∼4.9 V and a high capacity.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/cmatex/2011/cmatex.2011.23.issue-17/cm201305z/production/images/medium/cm-2011-01305z_0003.gif'></P>