Hydrothermally synthesized tin (IV) sulfide as a negative electrode for sodium-ion batteries and its sodiation mechanism

Kim, Hyun-seung,Kim, Jaekwang,Kim, Hyosung,Kim, Youngjin,Ryu, Ji Heon,Oh, Seung M.,Yoon, Songhun Elsevier 2018 Journal of Electroanalytical Chemistry Vol.808 No.-

<P><B>Abstract</B></P> <P>A hydrothermally synthesized tin (IV) sulfide electrode was examined for use as a negative electrode in sodium-ion batteries. Using ex-situ XRD and electrochemical analysis, the sodiation mechanism of tin (IV) sulfide was clarified, which revealed that the typical conversion reaction-coupled alloying reaction happened during sodiation with a high reversible capacity (~640mAhg<SUP>−1</SUP>). Also, the improved cycleability was observed in the tin (IV) sulfide electrode when compared with tin metal electrode. From comparison of quasi-open-circuit voltages at the 20th de-sodiated electrode, it was revealed that sodium trapping was considerably suppressed by sulfide formation with tin.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Hydrothermally-synthesized tin (IV) sulfide (SnS<SUB>2</SUB>) is applied as negative electrode for sodium-ion batteries. </LI> <LI> Hydrothermally-synthesized SnS<SUB>2</SUB> shows stable cycleability. </LI> <LI> The dead particle generation is very suppressed at SnS<SUB>2</SUB> negative electrode. </LI> </UL> </P>

Novel estimation method of operating life in lithium-ion pouch cells

Kim, Hyosung,Kim, Jaekwang,Kim, Nayeong,Lee, Ilbok,Hwang, Keebum,Bae, Joongho,Yoon, Songhun THE KOREAN SOCIETY OF INDUSTRIAL AND ENGINEERING 2018 JOURNAL OF INDUSTRIAL AND ENGINEERING CHEMISTRY -S Vol.67 No.-

<P><B>Abstract</B></P> <P>Herein, a novel operating life (OL) test method was evaluated with 200mAh pouch-type lithium-ion batteries. By combining the calendar life (CL) test with intermediate pulse power cycling, more realistic life prediction was possible, which encompassed real operation of batteries accompanying with thermal acceleration. Larger capacity decrease and resistance increase of pouch cell were observed in the OL test, which was well explained using the SEI film growth model. After dissemble of pouch cell, capacity loss and resistance increase mostly occurred within anode, reflecting that SEI film growth on anode surface was highly attributable to cell degradation.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Suggestion of novel operating life prediction. </LI> <LI> Intermediate pulse power cycling to simulate vehicle operation. </LI> <LI> Combination of pulse power cycling and thermal degradation by calendar life prediction. </LI> <LI> Surface film growth model to explain capacity and resistance change. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Ordered Mesoporous Carbon Imbedded with Nano Tungsten Oxide as Anode Material in Lithium Ion Batteries

Kim, Hyosung,Zhou, Yuanyuan,Kim, Jaekwang,Kim, Nayoung,Yoon, Songhun American Scientific Publishers 2017 Science Of Advanced Materials Vol.9 No.10

금융변수의 주가수익률 예측력 검정

김현석 ( Hyunseok Kim ),여효성 ( Hyosung Yeo ) 한국금융학회 2017 금융연구 Vol.31 No.1

본 연구는 한국주식시장을 대상으로 배당수익률, 이익주가 비율(E/P 비율), 이자율, Yield Gap과 같은 금융변수의 주가수익률 예측력을 검정하였다. 이를 위해 예측회귀분석 시 발생 가능한 계량적 문제들을 효과적으로 처리하기 위하여 Choi, Jacewitz, and Park(2016)의 변동성 시계 표본을 이용한 Cauchy 추정법을 적용하여 실증분석을 수행하였으며, 주요한 분석 결과는 다음과 같다. 첫째, 주가수익률의 QV(quadratic variation)을 기반으로 변동성 시계로 변환한 모형에서는 어떤 변수도 주가수익률 예측력을 가지지 못하는 것으로 나타났지만, 주가수익률의 BPV(bipower variation)을 기반으로 변동성 시계로 변환한 모형에서는 배당수익률이 주가수익률 예측력을 가지는 것으로 나타났다. 둘째, 장단기 Yield Gap의 주가수익률 예측력 검정 결과, 장단기 Yield Gap 중 어느 변수도 주가수익률 예측력을 가지지 못하는 것으로 나타났다. 본 연구는 금융변수의 주가수익률 예측력 검정 시 나타날 수 있는 다양한 문제들을 새로운 계량적 기법을 사용하여 효과적으로 처리하였다는 점에서 기존연구와 차별성을 가진다. 또한 주가수익률에 대한 예측 변수로서 선진금융시장에서 흔히 사용되는 Yield Gap을 소개하고, 이의 주가수익률 예측가능성을 추가적으로 검정하였다는 점에서 보다 진일보된 실증분석 연구로서의 의미를 갖는다. In this paper, we examine stock return predictability in the Korean stock market using the random time Cauchy estimator. Various financial variables have been tested for stock return predictability, but the results remain inconclusive. In the Korean stock market, Kim and Kim (2004), Kim and Park (2009) and Chung and Kim (2010) try to find evidence of return predictability using the dividend-price ratio, earnings-price ratio, and interest rates, but their conclusions are mixed. More recently, Choi et al. (2016) propose a robust test of stock return predictability which combines the time-change method with a Cauchy estimator. They show that the random time Cauchy test has an exact size of test and comparable power to Campbell and Yogo (2006) and Chen and Deo (2009)`s tests. We apply this new methodology to the KOSPI index and report the empirical results, providing comparison with other widely used tests for return predictability. Stock returns have nearly nonstationary stochastic volatility, and this causes substantial size distortions on standard tests relying on constant variance. To handle this nonstationary stochastic volatility in returns, we implement a simple time change. For the required time change, “we wait for volatility to reach a certain threshold before collecting each observation such that there is a constant level of volatility across all observations in our sample.”(Campbell and Yogo, 2006) Using the daily KOSPI index, we first test the presence of discrete jumps in our sample. We detect a total of 15 jumps between January 2001 and December 2014 with the windows size 16 and a 5% significance level, using Lee and Mykland (2008) test. Depending on the presence of discrete jumps, we measure the realized variance and realized bi-power variation. When we allow for only the continuous martingale in the regression error, we remove the detected daily jumps and compute the total realized variance by squaring and summing up daily excess returns. When we allow our continuous time regression model to have discrete jumps, we compute the realized total bi-power variation without removing detected jumps. We have a total of 168 months in our sample span. The computed total realized variance (TQV) and total realized bi-power variation (TBPV) are then divided by the number of months and we set this as our volatility threshold △<sub>QV</sub> and △<sub>BPV</sub> for a time change with QV and a time change with BPV, respectively. Using the given volatility threshold, we add up daily squared excess returns until it hits our set △ and resample our regression variables on that date and repeat the process until we reach the TQV and TBPV. After correcting for stochastic volatility in returns, we implement a Cauchy estimator to handle the persistent endogeneity of covariates. The Cauchy estimator uses the sign transform of a covariate as an instrumental variable. “The advantage of using a Cauchy estimator is that the asymptotic normality of the Cauchy t-ratio holds regardless of any statistical anomalies in covariates including nonstationarity, fat-tailed innovations, structural breaks, and jumps.” (Choi et al., 2016) Thus, it is well suited for testing return predictability in cases where many commonly used covariates are highly persistent and correlated with the regression residuals. Inferences using the Cauchy t-ratio are also valid even in the presence of structural breaks and jumps. We test for stock return predictability in the Korean market using the log of dividend-price ratio, the log of earnings-price ratio, the riskfree rate, and short-term, medium-term and long-term yield gaps. For the dividend-price ratio, conventional OLS t-test over-rejects the null hypothesis of no predictability. We could not find evidence for predictability using other tests except the random time Cauchy with BPV. For the earnings- price ratio, none of our tests reject the null. The coefficients of risk-free rates are insignificant except for Campbell and Yogo (2006)`s BQ test where its 90% confidence interval does not include zero value. Using the Amihud and Hurvich (2004) and Campbell and Yogo (2006)`s test, shortterm yield gap has predictive power. But using the Chen and Deo (2009)`s chi-square 1 and random time Cauchy t-test, we could not reject the null. After correcting for persistent endogeneity in the medium-term yield gap, evidence for return predictability disappears, and all our tests except for OLS t-test cannot reject the null. Finally, we could not find any evidence for predictability using the long-term yield gap.

Ternary halide Perovskites for Highly Efficient Solution-Processed Hybrid Solar Cells

Jaeki Jeong,Hak-Beom Kim,Haeyeon Kim,Bright Walker,Seyeong Song,Jungwoo Heo,Yung Jin Yoon,Yimhyun Jo,Hyosung Choi,Gi-Hwan Kim,Dong Suk Kim,Jin Young Kim 한국고분자학회 2016 한국고분자학회 학술대회 연구논문 초록집 Vol.41 No.2

A New Voxelization Strategy in Compressed-Sensing (CS)-Based Iterative CT Reconstruction for Reducing Computational Cost: Simulation and Experimental Studies

Kim, Guna,Park, Soyoung,Je, Uikyu,Cho, Hyosung,Park, Chulkyu,Kim, Kyuseok,Lim, Hyunwoo,Lee, Dongyeon,Lee, Hunwoo,Park, Yeonok,Woo, Taeho Springer-Verlag 2018 Journal of medical and biological engineering Vol.38 No.1

<P>In recent computed tomography (CT) reconstruction, iterative methods have been often used owing to the potential to provide three-dimensional (3D) images of superior reconstruction quality to common filtered-back-projection (FBP)-based methods. However, these methods require enormous computational cost in the iterative process, which has still been an obstacle to put them to practical use. In this work, to overcome these difficulties, we propose a new cone-beam CT reconstruction with a dual-resolution voxelization strategy for a small region-of-interest (ROI) reconstruction in which the voxels outside the target ROI are binned by, for example, 2 x 2 x 2, 4 x 4 x 4, 8 x 8 x 8, etc., while the other voxels remain unbinned. We considered a compressed-sensing (CS)based algorithm with a dual regularization strategy, rather than common FBP-based methods, for more accurate CT reconstruction. We implemented the proposed CS-based algorithm and performed a systematic simulation and experiment. Our results indicate that the proposed method seems to be effective for reducing computational cost considerably in iterative CT reconstruction, keeping the reconstruction quality inside the target ROI not much degraded.</P>

Definition of Power Quality Factors at The Point of Common Coupling in Single-Phase Systems and Three-Phase Systems

Hyosung Kim,Frede Blaabjerg,Birgitte Bak-Jensen 전력전자학회 2001 ICPE(ISPE)논문집 Vol.2001 No.10

This paper proposes an unified definition of powers for various circuit conditions such as balanced/unbalanced, sinusoidat/non-smusoidal, and linear/nonlinear, for single-phase systems and three-phase systems. Conventional reactive power is more classified into an interactive power and a scattering power. These powers are defined both in the time domain and the frequency domain consistently, and agree well with the conservation law. Several important power quality factors are defined to measure and evaluate the power quality for the various circuits in the single-phase and three-phase systems. Simulation results show the power quality factors can evaluate and classify the various circuit conditions clearly.<br/>

Polymerizable Supramolecular Approach to Highly Conductive PEDOT:PSS Patterns

Kim, Tae Geun,Ha, Su Ryong,Choi, Hyosung,Uh, Kyungchan,Kundapur, Umesha,Park, Sumin,Lee, Chan Woo,Lee, Sang-hwa,Kim, Jaeyong,Kim, Jong-Man American Chemical Society 2017 ACS APPLIED MATERIALS & INTERFACES Vol.9 No.22

<P>Owing to its high conductivity, solution processability, mechanical flexibility, and transparency, poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) has been extensively explored for use in functional devices including solar cells, sensors, light-emitting diodes, and supercapacitors. The ability to fabricate patterned PEDOT:PSS on a solid substrate is of significant importance to develop practical applications of this conducting polymer. Herein, we describe a new approach to obtain PEDOT:PSS patterns that are based on a polymerizable supramolecular concept. Specifically, we found that UV irradiation of a photopolymerizable diacetylene containing PEDOT:PSS film followed by development in deionized water and subsequent treatment with sulfuric acid (glass and silicon wafer) or formic acid (PET) produces micron-sized PEDOT:PSS patterns on solid substrates. The newly designed photolithographic method, which can be employed to generate highly conductive (>1000 S/cm) PEDOT:PSS patterns, has many advantages including the use of aqueous process conditions, a reduced number of process steps, and no requirement for plasma etching procedures.</P>

OPERATION MODES ANALYSIS FOR A DVR IN DISTRIBUTION GRIDS

Hyosung Kim,John Kim 전력전자학회 2001 ICPE(ISPE)논문집 Vol.2001 No.10

Recent power quality measurement projects report that voltage sags are the most frequent disturbances in the sites [l]-[4]. DVRs were emerged as the best effective and economic solution for this problem [11]. This paper analyzed the power flow of a DVR in distribution grids This paper showed various operation modes and boundanes such as inductive operation, capacitive operation, and minimal power operation beside the in-phase compensation.<br/>

Modeling for Series Arc of DC Circuit Breaker

Kim, Yong-Jung,Kim, Hyosung IEEE 2019 IEEE transactions on industry applications Vol.55 No.2

<P>In electric distribution systems, a series arc occurs when a load and a power source are disconnected from a connector such as a circuit breaker, a socket–plug, or a coupler. In dc systems, the arc is not extinguished unless the arc current decreases to zero. Sustaining plasma arc current can cause huge fire disasters. To cope with the arc faults in dc systems, the characteristics of the arc should be analyzed. However, a clear analysis method has not been suggested. This paper analyzes characteristics of a series-breaking arc in a dc circuit breaker in three operation phases: initiation, sustenance, and extinguishment. Based on the three operation characteristics, a series-breaking arc model is proposed and evaluated through experiment.</P>