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>

Reliable seawater battery anode: controlled sodium nucleation via deactivation of the current collector surface

Kim, Do Hyeong,Choi, Hongkyw,Hwang, Dae Yeon,Park, Jaehyun,Kim, Keun Soo,Ahn, Seokhoon,Kim, Youngsik,Kwak, Sang Kyu,Yu, Young-Jun,Kang, Seok Ju Royal Society of Chemistry 2018 Journal of Materials Chemistry A Vol.6 No.40

<P> Seawater battery, which consists of a Na metal anode and a seawater cathode, has highly attractive features because of its eco-friendliness in use of seawater and cost-effectiveness in the use of Na, the 6th most abundant element of the Earth's crust. Herein, we demonstrate a reliable Na metal anode for the seawater battery by covering the Cu current collector with a graphene monolayer. The surface of the chemically uniform graphene-coated current collector facilitates control of the nucleation rate of surficial Na metal at the initial stage and enhances the coulombic efficiency in current collector|separator|Na metal cells by lowering the nucleation and plating potentials. Further deliberate modification of the graphene surface by using O<SUB>2</SUB> plasma and thermal treatments supports the significance of the homogeneity of the interface of the current collector. Problematically, heterogeneous Cu surfaces covered with islands of oxide layers significantly altered the surface morphology of plated Na metal and consequently resulted in the decrease in electrochemical performance due to the impeding effect on Na ion diffusion near the current collector surface. Through successful implantation of the graphene-coated Cu current collector as an anode in the seawater battery, the battery performance drastically improved, which was confirmed by monitoring the discharge/charge performance and durability of LED lighting. </P>

Attention Deficit Hyperactivity Disorder Like Behavioral Problems and Parenting Stress in Pediatric Allergic Rhinitis

YoungSik Lee,SeHee Kim,JiHee You,HyungTae Baek,Chul Na,BungNyun Kim,DougHyun Han 대한신경정신의학회 2014 PSYCHIATRY INVESTIGATION Vol.11 No.3

Objective-Previous studies have reported comorbidity of attention deficit and hyperactivity disorder (ADHD) and allergic diseases. The current study investigated ADHD like behavioral symptoms and parenting stress in pediatric allergic rhinitis. Methods-Eighty-seven children (6-13 years old) with allergic rhinitis and 73 age- and sex-matched children of control group were recruited. Diagnosis and severity assessments of allergic rhinitis were determined by a pediatric allergist. The Parenting Stress Index-Short Form (PSI-SF), ADHD Rating Scale (ARS), and Child Behavior Checklist (CBCL) were completed by their mothers. Results-In the allergic rhinitis group, the total PSI-SF score (p<0.01), ARS score (p<0.01), the subscale scores of the CBCL including somatization, attentional problems and emotional instability (p=0.01; p<0.01; p<0.01) and prevalence of ADHD (p=0.03) were significantly higher than those of the control group. Among mothers of children with allergic rhinitis, those of children with comorbid ADHD demonstrated significantly higher parenting stress than those without comorbid ADHD (p<0.01). Parenting stress was correlated with severity of child’s allergic symptoms and the ARS total score (beta=0.50, p<0.01; beta=0.39, p<0.01). There was a significant correlation between allergic symptom severity and the ARS total score (B=8.4, SD=2.5, t=3.3, p<0.01). Conclusion-This study demonstrated that ADHD symptoms were common in children with allergic rhinitis, and this factor increased parenting stress and disrupted the parent-child relationship. Routine evaluation and early management of ADHD symptoms in pediatric allergic rhinitis may benefit families of children with allergic rhinitis.

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.

Comparison of Transparency Techniques in PSNRs Based on Deferred Rendering Using Multiple Render Targets

Youngsik Kim 보안공학연구지원센터 2016 International Journal of Multimedia and Ubiquitous Vol.11 No.11

In three dimensional (3D) computer games, the deferred rendering is an effective way to process realistic visual effects such as dynamic lights, shadow, depth of field (DOF), and high dynamic range (HDR) using multiple geometric buffers(G-buffers) regardless of the scene complexity. However, the G-buffer only stores information about a single pixel in each texel, so transparency with alpha blending on deferred rendering is difficult compared to forward rendering. The conventional way to process transparency on deferred rendering is to separate opaque and transparent renderings. But the object sorting required in it causes the speed degradation. Nevertheless the transparency techniques without object sorting such as screen door, interfaced, and stochastic can reduce the rendering time, but those cause the image quality degradation. This paper compares transparency techniques on deferred rendering. The Game Institute 3D game engine is modified to measure the rendering speeds of transparency techniques. The deferred rendering can speed up the rendering time of about 1.48 times than the forward rendering. The transparency techniques without object sorting can also speed up the rendering time of about 1.1 times than the conventional technique. Plus, six 4K ultra high definition (UHD) game images are used to measure the extent of quality degradation of the transparency techniques without object sorting in terms of peak noise signal ratio (PSNR). Consequently, the interlaced technique can get better PSNRs of about 124.8% in the same than both the screen door and the stochastic techniques.

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>

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

LiCl-LiI molten salt electrolyte with bismuth-lead positive electrode for liquid metal battery

Kim, Junsoo,Shin, Donghyeok,Jung, Youngjae,Hwang, Soo Min,Song, Taeseup,Kim, Youngsik,Paik, Ungyu Elsevier 2018 Journal of Power Sources Vol.377 No.-

<P><B>Abstract</B></P> <P>Liquid metal batteries (LMBs) are attractive energy storage device for large-scale energy storage system (ESS) due to the simple cell configuration and their high rate capability. The high operation temperature caused by high melting temperature of both the molten salt electrolyte and metal electrodes can induce the critical issues related to the maintenance cost and degradation of electrochemical properties resulting from the thermal corrosion of materials. Here, we report a new chemistry of LiCl-LiI electrolyte and Bi-Pb positive electrode to lower the operation temperature of Li-based LMBs and achieve the long-term stability. The cell (Li|LiCl-LiI|Bi-Pb) is operated at 410 °C by employing the LiCl-LiI (LiCl:LiI = 36:64 mol %) electrolyte and Bi-Pb alloy (Bi:Pb = 55.5:44.5 mol %) positive electrode. The cell shows excellent capacity retention (86.5%) and high Coulombic efficiencies over 99.3% at a high current density of 52 mA cm<SUP>−2</SUP> during 1000<SUP>th</SUP> cycles.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Electrochemical behavior of the material was investigated for liquid metal cells. </LI> <LI> Low operation temperature was achieved by the eutectic composition of LiCl-LiI. </LI> <LI> The wetting behavior of Bi-Pb alloy was studied on the current collector substrate. </LI> <LI> Li|LiCl-LiI|Bi-Pb cells showed long cycle, high efficiency, and high rate capability. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>