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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.
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>
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.
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.
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>
Chae, Byung-Mok,Oh, Eun-Suok,Lee, Yong-Kul Elsevier 2015 Journal of Power Sources Vol.274 No.-
<P><B>Abstract</B></P> <P>Co<SUB>3</SUB>O<SUB>4</SUB> powders as anode active materials for Li-ion battery are synthesized by a simple precipitation method. Physical properties of the prepared Co<SUB>3</SUB>O<SUB>4</SUB> are characterized by N<SUB>2</SUB> physisorption, transmission electron microscopy, and X-ray diffraction. Conversion mechanisms upon the structural changes of Co<SUB>3</SUB>O<SUB>4</SUB> anode are thoroughly studied by an in situ X-ray absorption fine structure (XAFS) technique. In the first cycle of discharge/charge, the X-ray absorption near-edge structure of Co reveals that the 1.1 V plateau of the discharging is ascribed to the direct conversion of Co<SUB>3</SUB>O<SUB>4</SUB> to Co metal, and the 2.0 V plateau of the charging to the conversion of Co metal to CoO and Co<SUB>3</SUB>O<SUB>4</SUB>. In the second cycle of discharge/charge, the XAFS analysis reveals that a part of Co metal phase remains unconverted due to the phase isolation. It is demonstrated that the addition of a conductive material can significantly improve the redox reaction of the Co<SUB>3</SUB>O<SUB>4</SUB> anode material by minimizing the phase isolation.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A direct conversion between Co<SUB>3</SUB>O<SUB>4</SUB> and Co was confirmed by in situ XAFS technique. </LI> <LI> A part of Co nano-particles can be electrically isolated during the cyclic test. </LI> <LI> The isolated Co particles can lose conductivity by a polymer layer or Li<SUB>2</SUB>O matrix. </LI> <LI> Addition of a conductive material improves the reversible redox capability. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>