Optimized hard carbon derived from starch for rechargeable seawater batteries

Kim, Yongil,Kim, Jae-Kwang,Vaalma, Christoph,Bae, Geun Hyeong,Kim, Guk-Tae,Passerini, Stefano,Kim, Youngsik Elsevier 2018 Carbon Vol.129 No.-

<P><B>Abstract</B></P> <P>The recently introduced seawater battery concept is an eco-friendly energy storage system that offers appealing electrochemical performance. Its radically innovative design, compared to conventional lithium-ion batteries, makes use of seawater as an almost infinite sodium reservoir for the positive electrode and, thereby, avoids the use of expensive, scarce, and toxic elements like nickel and cobalt. So far, the problems identified mostly originate from the available negative electrode active materials. In this study, a starch-derived hard carbon was used to optimize the system. Due to its improved disordered structure compared with commercial hard carbon, the starch hard carbon exhibits an increased reversible capacity, current-rate capability, and cycling ability. The material, in fact, depicts a high maximum power density of 700 W kg<SUP>−1</SUP> (based on hard carbon weight) upon discharge at 900 mA g<SUP>−1</SUP>, while still being active at 2700 mA g<SUP>−1</SUP>. These results represent an important step toward practical application of the sodium-based seawater battery technology.</P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Improving the Linearity of CMOS LNA Using the Post IM3 Compensator

Jingook Kim,Changjoon Park,Huijung Kim,Bumman Kim,Youngsik Kim 한국전자파학회JEES 2007 Journal of Electromagnetic Engineering and Science Vol.7 No.2

In this paper, a new linearization method has been proposed for a CMOS low noise amplifier(LNA) using the Post IM3 Compensator. The fundamental operating theory of the proposed method is to cancel the IM3 components of the LNA output signal by generating another IM3 components, which are out-phase with respect to that of the LNA, from the Post IM3 Compensator. A single stage common-source LNA has been designed to verify the linearity improvement of the proposed method through 0.13 ㎛ RF CMOS process for WiBro system. The designed LNA achieves +7.8 ㏈m of input-referred 3<SUP>rd</SUP>-order intercept point (ⅡP3) with 13.2 ㏈ of Power Gain, 1.3 ㏈ of noise figure and 5.7 mA @1.5 V power consumption. IIP3 is compared with a conventional single stage common-source LNA, and it shows IIP3 is increased by +12.5 ㏈ without degrading other features such as gain and noise figure.

A hybrid solid electrolyte for flexible solid-state sodium batteries

Kim, Jae-Kwang,Lim, Young Jun,Kim, Hyojin,Cho, Gyu-Bong,Kim, Youngsik The Royal Society of Chemistry 2015 Energy & environmental science Vol.8 No.12

<P>Development of Na-ion battery electrolyte with high-performance electrochemical properties and high safety is still challenging to achieve. In this study, we report on a NASICON (Na<SUB>3</SUB>Zr<SUB>2</SUB>Si<SUB>2</SUB>PO<SUB>12</SUB>)-based composite hybrid solid electrolyte (HSE) designed for use in a high safety solid-state sodium battery for the first time. The composite HSE design yields the required solid-state electrolyte properties for this application, including high ionic conductivity, a wide electrochemical window, and high thermal stability. The solid-state batteries of half-cell type exhibit an initial discharge capacity of 330 and 131 mA h g<SUP>−1</SUP> for a hard carbon anode and a NaFePO<SUB>4</SUB> cathode at a 0.2C-rate of room temperature, respectively. Moreover, a pouch-type flexible solid-state full-cell comprising hard carbon/HSE/NaFePO<SUB>4</SUB> exhibits a highly reversible electrochemical reaction, high specific capacity, and a good, stable cycle life with high flexibility.</P> <P>Graphic Abstract</P><P>Ceramic-based hybrid solid electrolyte (HSE) is designed to build a flexible pouch-type Na-ion battery. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c5ee01941a'> </P>

Dependence of planar alignment layer upon enhancement of azimuthal anchoring energy by reactive mesogens

Kim, Youngsik,Lee, You-Jin,Baek, Ji-Ho,Yu, Chang-Jae,Kim, Jae-Hoon Institute of Pure and Applied Physics 2015 Japanese Journal of Applied Physics Vol.54 No.1

광대역 TRAO CO 관측: 분자운 충돌

Kim Youngsik,Kim Kwang Tae,Lee Youngung 한국천문학회 2015 天文學會報 Vol.40 No.2

MIRIS Pa <i>α</i> Galactic Plane Survey. I. Comparison with IPHAS H <i>α</i> in <i>ℓ</i> = 96°-116°

Kim, Il-Joong,Pyo, Jeonghyun,Jeong, Woong-Seob,Seon, Kwang-Il,Nakagawa, Takao,Kim, Min Gyu,Park, Won-Kee,Lee, Dae-Hee,Lee, Dukhang,Moon, Bongkon,Park, Sung-Joon,Park, Youngsik,Matsumoto, Toshio,Han, W American Astronomical Society 2018 The Astrophysical journal Supplement series Vol.238 No.2

<P>The Multipurpose InfraRed Imaging System (MIRIS) performed the MIRIS Pact Galactic Plane Survey (MIPAPS), which covers the entire Galactic plane within the latitude range of -3 degrees less than or similar to b less than or similar to +3 degrees at Pa alpha (1.87 mu m). We present the first result of the MIPAPS data extracted from the longitude range of l = 96 degrees.5-116.degrees 3 and demonstrate the quality and scientific potential of the data by comparing them with Ha maps obtained from the INT Photometric H alpha Survey (IPHAS) data. We newly identify 90 H II region candidates in the WISE H II region catalog as definite H II regions by detecting the Pa alpha and/or H alpha recombination lines, out of which 53 H II regions are detected at Pa alpha. We also report the detection of an additional 29 extended and 18 point-like sources at Pa alpha. We estimate the E(B-V) color excesses and total Lyman continuum luminosities for H II regions by combining the MIPAPS Pact and IPHAS H alpha fluxes. The E(B-V) values are found to be systematically lower than those estimated from point stars associated with H II regions. Utilizing the MIPAPS Pact and IPHAS H alpha images, we obtain an E(B-V) map for the entire region of the H II region Sh2-131 with an angular size of -2 degrees.5. The E(B-V) map shows not only numerous high-extinction filamentary features but also negative E(B-V) regions, indicating H alpha excess. The Ha excess and systematic underestimation of E(B-V) are attributed to light scattered by dust.</P>

경남 일부 지역 여자 대학생의 상하체 균형 계측치와 운동 습관

Youngsik Kim(김영식),Imsil Yoon(윤임실),Wonjoon Lee(이원준),Jeongsu Nam(남정수),Joongsoo Yoon(윤중수),Ryeamin Youn(윤려민),Hanna Jung(정한나),Jaeshik Ko(고재식),Hyunju Choi(최현주) 한국생명과학회 2010 생명과학회지 Vol.20 No.4

경남지역 모 대학교에 재학 중인 여자 대학생 212명을 대상으로 인체 계측과 건강에 관련된 습관에 대하여 설문 조사를 실시하였다. 총대상자의 평균 연령은 20.7 세, 신장은 161.8 ㎝, 체중은 53.5 ㎏이었으며, 비만도는 98.4%이었으며 체질량 지수는 20.6 ㎏/㎡이었고 허리-엉덩이 둘레 비율은 0.80이었다. 이와 같은 신체 계측치는 한국인의 정상 범위에 속하는 것이지만, 조사 대상자의 63.7%가 상체가 하체에 비하여서 불균형적으로 약한 체형인 것으로 나타났다. 이들 대상자를 불균형적으로 상체가 약한 군(UU, n=135)으로 하고 대조군으로써 상ㆍ하체가 균형인 군(BU, n=77)의 두 군으로 나누어서 측정 결과치를 비교 분석하였다. 체중, 비만도, 체질량지수, 허리-엉덩이 둘레비가 BU군에 비하여서 UU군이 유의적으로 낮았다. 체단백짙, 체지방, 체무기짙량도 역시 UU군에서 유의적으로 낮았다. 상완근육 둘레를 측정한 결과, UU군이 BU군에 비하여 유의적으로 낮았다. 운동의 규칙적 수행여부를 알아본 결과 UU군의 1.5%, BU군에서 7.8%가 ‘운동을 규칙적으로 하고 있다’고 답하였다. 한편 ‘운동을 전혀 하고 있지 않다’라고 답한 비율이 UU군과 BU군에서 각각 55.5%, 31.2%로써, 운동을 하지 않는 경우가 UU군에서 1.8배 정도 많았다. 운동을 할 경우에 얼마나 오래하는지에 대한 질문에 UU군의 38.4%와 BU군의 35.8%가 30분 이하로 운동을 한다고 답하여서, 여자 대학생이 운동을 한다 하더라도 운동 시간이 충분하지 않은 것으로 사료된다. 본 연구 조사 결과, 상체가 하체에 비하여서 불균형적으로 약한 여자 대학생이 총 조사 대상자의 63.7%이나 되었으며, 이들의 운동 습관에 문제가 있는 것으로 나타나서 운동을 습관화하여 꾸준히 하고 특히 상체와 팔 근육을 발달시키는 운동을 실천하는 것이 필요하다고 사료된다. 아울러 여자 대학생만을 대상으로 하여 체형의 올바른 인식을 위한 교육의 필요성이 절실하며, 신체 부위의 균형을 고려한 운동 프로그램 개발이 시급하다고 생각한다. This study was carried out to examine anthropometric parameters and related habits in female college students. Mean age, height, and body weight of the subjects in total (n=212) were 20.7 yrs, 161.8 ㎝, and 53.5 ㎏, respectively. Anthropometric parameters were measured by bioelectrical impedance analysis. Mean degree of obesity, body mass index (BMI), and waist-hip ratio (WHR) were 98.4%, 20.6 ㎏/㎡, and 0.80 respectively. Surprisingly, 63.7% of the subjects showed unbalanced weak upper bodies compared to their lower bodies. Therefore, they were divided into two groups: unbalanced weak upper body group (UU, n=135) and balanced upper body groups (BU, n=77). Bodyweight, degree of obesity, BMI, and WHR in the UU group were significantly lower than those in the BU group. Amounts of body protein, body fat, and body mineral in the UU group were also significantly lower than those of the BU group. Mid-arm muscle circumference of the UU group (18.5±0.8 ㎝) was significantly lower than those of BU group (20.4±1.2 ㎝), although mid-arm circumference of the UU group was not significantly different compared to those of the BU group. On a questionnaire on exercise habits, 1.5% of the UU group and 7.8% of the BU group answered that they exercised regularly, and 55.5% of the UU group and 31.2% of the BU group reported that they never exercised (p<0.01). Even in the subjects who exercised, the duration of the exercise was not sufficient because 38.4% of the UU group and 35.8% of the BU group answered that they exercised for less than 30 min. In conclusion, interventions in exercise habits may be needed for female college students who have unbalanced weak upper bodies.

Free vibrations of an annular sector bimorph plate

Youngsik Kim,Pilki Kim,Jongwon Seok 대한기계학회 2006 대한기계학회 춘추학술대회 Vol.2006 No.11

An analysis of the flexural vibrations of an annular sector bimorph plate is performed by means of a variational approximation procedure. The bimorph plate is clamped on the outer circumferential edge and free on the other three. The method of separation of variable is used and the solution functions satisfying differential equation in radial direction are obtained by introducing a Frobenius type expansion. To evaluate the eigenfrequencies and the associated eigenmodes, the dispersion relations of the circumferential- and radial-directional flexural waves are obtained first, where these relations satisfy the edge conditions on the two facing circumferential edges exactly. The waves satisfying the dispersion relations are employed as the solution funnctions for the remaining part of the variational equation, where all conditions occur as natural type. The resulting eigensolutions, which satisfy the remaining part variationally, are compared with those obtained from an FE analysis.

New Chemical Route for the Synthesis of β-Na_0.33V₂O₅ and Its Fully Reversible Li Intercalation

Kim, Jae-Kwang,Senthilkumar, B.,Sahgong, Sun Hye,Kim, Jung-Hyun,Chi, Miaofang,Kim, Youngsik American Chemical Society 2015 ACS APPLIED MATERIALS & INTERFACES Vol.7 No.12

<P>To obtain good electrochemical performance and thermal stability of rechargeable batteries, various cathode materials have been explored including NaVS<SUB>2</SUB>, β-Na<SUB>0.33</SUB>V<SUB>2</SUB>O<SUB>5</SUB>, and Li<SUB><I>x</I></SUB>V<SUB>2</SUB>O<SUB>5</SUB>. In particular, Li<SUB><I>x</I></SUB>V<SUB>2</SUB>O<SUB>5</SUB> has attracted attention as a cathode material in Li-ion batteries owing to its large theoretical capacity, but its stable electrochemical cycling (i.e., reversibility) still remains as a challenge and strongly depends on its synthesis methods. In this study, we prepared the Li<SUB><I>x</I></SUB>V<SUB>2</SUB>O<SUB>5</SUB> from electrochemical ion exchange of β-Na<SUB>0.33</SUB>V<SUB>2</SUB>O<SUB>5</SUB>, which is obtained by chemical conversion of NaVS<SUB>2</SUB> in air at high temperatures. Crystal structure and particle morphology of β-Na<SUB>0.33</SUB>V<SUB>2</SUB>O<SUB>5</SUB> are characterized by using X-ray diffraction, scanning electron microscopy, and transmission electron microscopy techniques. Energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy, in combination with electrochemical data, suggest that Na ions are extracted from β-Na<SUB>0.33</SUB>V<SUB>2</SUB>O<SUB>5</SUB> without irreversible structural collapse and replaced with Li ions during the following intercalation (i.e., charging) process. The thus obtained Li<SUB><I>x</I></SUB>V<SUB>2</SUB>O<SUB>5</SUB> delivers a high discharge capacity of 295 mAh g<SUP>–1</SUP>, which corresponds to <I>x</I> = 2, with crystal structural stability in the voltage range of 1.5–4.0 V versus<SUB>.</SUB> Li, as evidenced by its good cycling performance and high Coulombic efficiency (under 0.1 mA cm<SUP>–2</SUP>) at room temperature. Furthermore, the ion-exchanged Li<SUB><I>x</I></SUB>V<SUB>2</SUB>O<SUB>5</SUB> from β-Na<SUB>0.33</SUB>V<SUB>2</SUB>O<SUB>5</SUB> shows stable electrochemical behavior without structural collapse, even at a case of deep discharge to 1.5 V versus Li.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/aamick/2015/aamick.2015.7.issue-12/acsami.5b01260/production/images/medium/am-2015-01260h_0006.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/am5b01260'>ACS Electronic Supporting Info</A></P>

Cloud-like graphene nanoplatelets on Nd_0.5Sr_0.5CoO_3−δ nanorods as an efficient bifunctional electrocatalyst for hybrid Li–air batteries

Kim, Changmin,Gwon, Ohhun,Jeon, In-Yup,Kim, Youngsik,Shin, Jeeyoung,Ju, Young-Wan,Baek, Jong-Beom,Kim, Guntae The Royal Society of Chemistry 2016 Journal of Materials Chemistry A Vol.4 No.6

<▼1><P>Benefiting from the unique morphological features, NSC@IGnP provides superior bifunctional activities toward both ORR and OER for hybrid Li-air batteries.</P></▼1><▼2><P>With the recognition of metal–air batteries as promising candidates for clean and efficient energy storage, the development of inexpensive and effective bifunctional catalysts for the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) has become one of the most important topics in this field. Herein, we designed new composite catalysts consisting of a nanorod type Nd0.5Sr0.5CoO3−δ (NSC) perovskite and edge-iodinated graphene nanoplatelets (IGnPs) as bifunctional catalysts for ORR and OER. Interestingly, the simple application of ultrasonication endowed the catalyst with a fascinating morphology comprising cloud-like IGnPs on NSC nanorods (NSC@IGnP). Benefiting from the unique morphological features, NSC@IGnP provides superior bifunctional activities toward both ORR and OER, remarkable cell performance, and exceptionally high stability for hybrid Li–air batteries.</P></▼2>