van der Waals Interaction Energies between Non-Planar Bodies

Oh, Eun Suok 한국화학공학회 2004 Korean Journal of Chemical Engineering Vol.21 No.2

The van der Waals interaction energies between non-planar geometries are obtained without the assumption that the distance between two non-planar bodies is much smaller than radii of the non-planar bodies. Based on atom-to-body van der Waals energies, we calculate body-to-body van der Waals interaction energies for several non-planar geometries. Using the continuum approach, we discuss the van der Waals interactions in two-dimensional carbon nanotubes and C_(60) molecules.

Effect of emulsified polymer binders on the performance of activated carbon electrochemical double-layer capacitors

Eun-Suok Oh,Seul Lee,Bolormaa Gendensuren,Boyeon Kim,Sangik Jeon,Young-Hyun Cho,Taewon Kim 한국화학공학회 2019 Korean Journal of Chemical Engineering Vol.36 No.11

The electrochemical properties of two water-emulsified polymers, styrene-butadiene rubber, and polytetrafluoroethylene, on activated carbon electrochemical capacitors were systematically compared. All electrodes were fabricated with different ratios of styrene-butadiene rubber and polytetrafluoroethylene: 4 : 0, 3 : 1, 2 : 2, and 1 : 3. A good dispersion of styrene-butadiene rubber nanoparticles maintains mesopores in activated carbon, whereas an increase in polytetrafluoroethylene binder content in the electrodes reduces mesoporous surface area significantly due to the lump polytetrafluoroethylene structure coagulated by smashed particles in water. The relatively strong adhesion of the styrene- butadiene rubber binder also leads to better cyclability for extremely long cycles and the rate capability with various current densities at room temperature. At a high temperature of 60 oC, however, the electrodes containing polytetrafluoroethylene binder showed comparable high specific capacitance due to the high thermal stability of polytetrafluoroethylene.

수첨탈황반응 촉매의 비활성화와 재생에 관한 연구

오은석(Eun Suok Oh),박용철(Yong Chul Park),이인철(In Chul Lee),이현구(Hyun Ku Rhee) 한국화학공학회 1995 화학공학의이론과응용 Vol.1 No.2

수첨탈황촉매의 제 2 촉진제로서 Ni 의 역활

오은석(Eun Suok Oh),한평현(Pyung Hyun Han),박용철(Yong Chul Park),이현구(Hyun Ku Rhee) 한국화학공학회 1996 화학공학의이론과응용 Vol.2 No.1

필기체 한글에서 자모 분리와 인식

이은주(Eun Joo Rhee),권오석(Oh Suok Kwon),김태균(Tae Kyun Kim) 한국정보과학회 1988 정보과학회논문지 Vol.15 No.6

본 논문에서는 필기체 한글에서 자모 분리와 인식을 위한 알고리즘을 제안하였다. 한글 인식은 한글의 구조와 필기체 한글이 갖는 특성에 따라 종모음 우선 추정에 의한 인식 방법을 택하여, 인식을 종모음 추정, 초성 인식, 종모음 복귀, 횡모음 인식, 종모음 인식, 종성 인식순으로 행하였다. 여기서, 자음의 분리와 인식은 필기체 한글에 적합한 기본 패턴을 정의하고 생성 문법에 의한 구문 해석으로, 또 모음의 분리와 인식은 모음 분리 및 인식 알고리즘에 의하여 이루어졌다. 그런데 한글 인식에 있어서 종모음을 우선 추정함으로 오류 발생의 원인이 완화되었고, 또 필기체 한글에 적합한 기본 패턴의 정의와 모음 분리 알고리즘을 제안함으로 필기체 한글이 갖는 패턴 변형을 효율적으로 수용할 수 있었다. 이에 따라 인식 알고리즘의 패턴 변형에 대한 유연성과, 인식 효율이 증가되었다. 제안한 인식 알고리즘에 대한 컴퓨터 모의 실험에서 93%의 정인식률을 얻어, 필기체 한글 인식에 있어서 본 알고리즘의 유용성을 확인하였다. This paper proposed the algorithm for the phonemic segmentation and recognition of handwritten Korean character(HANGEUL) The Korean characters are recognized by the following procedures according to the structure of Korean characters and the characteristics of handwritten Korean characters estimation of vertical vowel, recognition of first consonant, return of vertical vowel, recognition of horizontal and vertical vowel, and recognition of last consonant. The consonant segmentation and recognition are performed by definding the primitive patterns which represent the corresponding handwritten Korean characters and analyzing syntax by the Tree grammar. The vowel segmentation and recognition require the extraction and recognition algorithm of vowel. The computer simulation result shows that the correct recognition ratio is 93% and thus this algorithm can be utilized in recognizing handrwitten Korean characters.

Effects of binder content on manganese dissolution and electrochemical performances of spinel lithium manganese oxide cathodes for lithium ion batteries

Kim, Eun-Young,Lee, Bo-Ram,Yun, Giyeong,Oh, Eun-Suok,Lee, Hochun Elsevier 2015 CURRENT APPLIED PHYSICS Vol.15 No.4

<P><B>Abstract</B></P> <P>In this study, the effects of the polyvinylidene fluoride (PVdF) binder on the Mn dissolution behavior and electrochemical performances of LiMn<SUB>2</SUB>O<SUB>4</SUB> (LMO) electrodes are investigated. It is found that increasing the PVdF content (3, 5, 7, and 10 wt.%) leads to reduced Mn dissolution, and thus superior cycle performance at elevated temperature (60 °C). This can be ascribed to increased binder coverage on the LMO surface, as evidenced by X-ray photoelectron spectroscopy measurements, which acts a role as a passivation layer for Mn dissolution. The rate capability of the LMO electrode is hardly deteriorated as the PVdF content increases, despite the increasing surface coverage. Electrochemical impedance measurements reveal that the LMO electrode with higher binder loading exhibits lower electrode impedance, which is suggested to be due to enhanced electronic passage through the composite LMO electrode.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Spinel LMO electrodes are fabricated with 3–10 wt.% PVdF binder content. </LI> <LI> Increased binder content leads to reduced Mn dissolution and superior cyclability at 60 °C. </LI> <LI> Rate capability is not deteriorated by increased PVdF content. </LI> <LI> LMO electrodes with higher binder content exhibit lower electrode impedance. </LI> </UL> </P>

Dual-crosslinked network binder of alginate with polyacrylamide for silicon/graphite anodes of lithium ion battery

Gendensuren, Bolormaa,Oh, Eun-Suok Elsevier Sequoia 2018 Journal of Power Sources Vol. No.

<P><B>ABsTRACT</B></P> <P>In lithium ion batteries, high-capacity anodes that undergo very large volume change during charge/discharge cycles are needed to apply a strongly adhesive polymer binder due to the severe mechanical stress developed during the cycles. Although bio-derived alginate is known to be a potential candidate for the binder owing to its strong mechanical property, it can be improved using a number of modifications such as physical crosslinking. Here, we propose a significantly better method of improving the electrochemical performance of the binder by introducing dual-crosslinked alginate with polyacrylamide. The polyacrylamide provides strong adhesion in the electrode with resistance to the penetration of the organic electrolyte. Both ionic and covalent crosslinkings in the binder maintain their intrinsic good binding properties and additionally enhance lithium ion diffusion. More interestingly, an in-situ electrochemical dilatometer study indicates that the dual-crosslinked binder is considerably helpful to prevent volume expansion beyond the inevitable value caused by active materials in electrodes during the cycle. Consequently, the Si/C (1/3) electrode retains nearly 840 mAh g<SUP>−1</SUP> high capacity even after one hundred cycles with excellent cycleability.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A bio-derived alginate is grafted with a strongly adhesive polyacrylamide. </LI> <LI> The dual-crosslinking is achieved by ionic and chemical crosslinkers. </LI> <LI> The dual-crosslinked binder has strong adhesion with low electrolyte uptakes. </LI> <LI> The dual-crosslinked binder helps to prevent extra volume expansion during cycle. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

3D Si/C particulate nanocomposites internally wired with graphene networks for high energy and stable batteries

Kim, Jaegyeong,Oh, Changil,Chae, Changju,Yeom, Dae-Hoon,Choi, Jaeho,Kim, Nahyeon,Oh, Eun-Suok,Lee, Jung Kyoo The Royal Society of Chemistry 2015 Journal of Materials Chemistry A Vol.3 No.36

<▼1><P>Novel 3D particulate Si/C-IWGNs (Si/C composites internally wired with graphene networks), in which graphene networks not only provide electrical networks but generate void spaces, showed stable cycling behavior at high capacity with a small increase in electrode thickness.</P></▼1><▼2><P>It is challenging to design silicon anodes exhibiting stable cycling behavior, high volumetric and specific capacity, and low volume expansion for Li-based batteries. Herein, we designed Si/C-IWGN composites (Si/C composites internally wired with graphene networks). For this purpose, we used simple aqueous sol–gel systems consisting of varying amounts of silicon nanoparticles, resorcinol–formaldehyde, and graphene oxide. We found that a small amount of graphene (1–10 wt%) in Si/C-IWGNs efficiently stabilized their cycling behavior. The enhanced cycling stability of Si/C-IWGNs could be ascribed to the following facts: (1) ideally dispersed graphene networks were formed in the composites, (2) these graphene networks also created enough void spaces for silicon to expand and contract with the electrode thickness increase comparable to that of graphite. Furthermore, properly designed Si/C-IWGNs exhibited a high volumetric capacity of ∼141% greater than that of commercial graphite. Finally, a hybrid sample, Si–Gr, consisting of a high capacity Si/C-IWGN and graphite was prepared to demonstrate a hybrid strategy for a reliable and cost-effective anode with a capacity level required for high-energy Li-ion cells. The Si–Gr hybrid exhibited not only high capacity (800–900 mA h g<SUP>−1</SUP> at 100 mA g<SUP>−1</SUP>) but also a high electrode volumetric capacity of 161% greater than that of graphite.</P></▼2>

Nanomechanical properties of polymer binders for Li-ion batteries probed with colloidal probe atomic force microscopy

Nguyen, Quang Dang,Oh, Eun-Suok,Chung, Koo-Hyun Applied Science Publishers 2019 Polymer Testing Vol. No.

<P><B>Abstract</B></P> <P>The nanomechanical properties of various polymer binders for lithium-ion batteries were assessed using colloidal probe atomic force microscopy (AFM) in air and in electrolyte. The reduced elastic moduli determined for polyacrylic acid (PAA), polyacrylonitrile (PAN), polyvinyl alcohol (PVA), carboxymethyl cellulose (CMC), and polyvinylidene fluoride (PVDF) were 3.3 ± 1.3, 1.1 ± 0.4, 1.4 ± 0.4, 5.0 ± 2.5, and 1.4 ± 0.6 GPa in air, respectively, and 210 ± 70, 220 ± 130, 410 ± 150, 140 ± 50, and 5.4 ± 2.6 MPa after immersion in electrolyte for 14 h. The results suggest that the effect of friction on force-indentation data should be considered, particularly for measurements in air. It was shown that PAA, PAN, PVA, and CMC are more advantageous than PVDF in terms of mechanical properties. Also, PAA and CMC are preferred due to their enhanced adhesion properties resulting from lower surface roughness and greater work of adhesion. The outcomes provide information to help understand the effects of electrolyte on material properties of polymer binders, which is useful to improve the electrochemical stability of the electrode. Also, the approach used in this work may aid in more accurate measurement of mechanical properties using AFM.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Effect of electrolyte on the surface structures of polymer binders for lithium-ion batteries. </LI> <LI> Significant decrease in elastic modulus of polymer binders in electrolyte. </LI> <LI> Determination of the work of adhesion of polymer binders. </LI> <LI> Effect of friction on force-indentation data of polymer binders in air. </LI> <LI> Significant decrease in frictional properties of polymer binders in electrolyte. </LI> </UL> </P>

Effect of Molecular Weight and Degree of Substitution of a Sodium-Carboxymethyl Cellulose Binder on Li₄Ti₅O₁₂ Anodic Performance

Lee, Bo-Ram,Oh, Eun-Suok American Chemical Society 2013 JOURNAL OF PHYSICAL CHEMISTRY C - Vol.117 No.9

<P>This paper presents a detailed investigation of the influence of molecular weight (MW) and degree of substitution (DS) of sodium-carboxymethyl cellulose (CMC) used as binder of Li<SUB>4</SUB>Ti<SUB>5</SUB>O<SUB>12</SUB> (LTO) anodes. CMC MW and DS were in the range of 90 000 to 700 000 and 0.7 to 1.2, respectively. As demonstrated by coin cell tests, the LTO electrode that contained relatively low MW and high DS CMC showed excellent cyclic performance above 150 mAh g<SUP>–1</SUP> even after 100 cycles. Unlike typical electrodes, the adhesion strength of the LTO electrodes was not a critical factor for cell performance. On the contrary, low coverage of CMC on the surface of LTO, which leads to weak adhesion, was more favorable to the cell performance than strong adhesion caused by high coverage. Both an increase in the DS and a decrease in the MW of CMC gave rise to low charge transfer resistance, high ion conductivity, good wettability with the electrolyte, and good lithium ion mobility owing to a relatively large amount of LTO exposed to directly the electrolyte so long as critical adhesion is guaranteed in the LTO electrode.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jpccck/2013/jpccck.2013.117.issue-9/jp311678p/production/images/medium/jp-2012-11678p_0009.gif'></P>