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141 results on '"Lee, Myeong Hwan"'

1. A Fiber‐Based 3D Lithium Host for Lean Electrolyte Lithium Metal Batteries

Author

Yu, Sicen, Wu, Zhaohui, Holoubek, John, Liu, Haodong, Hopkins, Emma, Xiao, Yuxuan, Xing, Xing, Lee, Myeong Hwan, and Liu, Ping

Subjects
Affordable and Clean Energy, 3D host, high porosity, lithium metal anode, RbNO3, vapor-grown carbon fiber
Abstract

3D hosts are promising to extend the cycle life of lithium metal anodes but have rarely been implemented with lean electrolytes thus impacting the practical cell energy density. To overcome this challenge, a 3D host that is lightweight and easy to fabricate with optimum pore size that enables full utilization of its pore volume, essential for lean electrolyte operations, is reported. The host is fabricated by casting a VGCF (vapor-grown carbon fiber)-based slurry loaded with a sparingly soluble rubidium nitrate salt as an additive. The network of fibers generates uniform pores of ≈3 µm in diameter with a porosity of 80%, while the nitrate additive enhances lithiophilicity. This 3D host delivers an average coulombic efficiency of 99.36% at 1 mA cm-2 and 1 mAh cm-2 for over 860 cycles in half-cell tests. Full cells containing an anode with 1.35-fold excess lithium paired with LiNi0.8 Mn0.1 Co0.1 O2 (NMC811) cathodes exhibit capacity retention of 80% over 176 cycles at C/2 under a lean electrolyte condition of 3 g Ah-1 . This work provides a facile and scalable method to advance 3D lithium hosts closer to practical lithium-metal batteries.

Published
2022

4. Voltage decay and redox asymmetry mitigation by reversible cation migration in lithium-rich layered oxide electrodes.

Author

Eum, Donggun, Kim, Byunghoon, Kim, Sung Joo, Park, Hyeokjun, Wu, Jinpeng, Cho, Sung-Pyo, Yoon, Gabin, Lee, Myeong Hwan, Jung, Sung-Kyun, Yang, Wanli, Seong, Won Mo, Ku, Kyojin, Tamwattana, Orapa, Park, Sung Kwan, Hwang, Insang, and Kang, Kisuk

Subjects
Nanoscience & Nanotechnology
Abstract

Despite the high energy density of lithium-rich layered-oxide electrodes, their real-world implementation in batteries is hindered by the substantial voltage decay on cycling. This voltage decay is widely accepted to mainly originate from progressive structural rearrangements involving irreversible transition-metal migration. As prevention of this spontaneous cation migration has proven difficult, a paradigm shift toward management of its reversibility is needed. Herein, we demonstrate that the reversibility of the cation migration of lithium-rich nickel manganese oxides can be remarkably improved by altering the oxygen stacking sequences in the layered structure and thereby dramatically reducing the voltage decay. The preeminent intra-cycle reversibility of the cation migration is experimentally visualized, and first-principles calculations reveal that an O2-type structure restricts the movements of transition metals within the Li layer, which effectively streamlines the returning migration path of the transition metals. Furthermore, we propose that the enhanced reversibility mitigates the asymmetry of the anionic redox in conventional lithium-rich electrodes, promoting the high-potential anionic reduction, thereby reducing the subsequent voltage hysteresis. Our findings demonstrate that regulating the reversibility of the cation migration is a practical strategy to reduce voltage decay and hysteresis in lithium-rich layered materials.

Published
2020

6. Toward a low-cost high-voltage sodium aqueous rechargeable battery

Author

Lee, Myeong Hwan, Kim, Sung Joo, Chang, Donghee, Kim, Jinsoo, Moon, Sehwan, Oh, Kyungbae, Park, Kyu-Young, Seong, Won Mo, Park, Hyeokjun, Kwon, Giyun, Lee, Byungju, and Kang, Kisuk

Subjects
Affordable and Clean Energy, Chemical Sciences, Engineering, Materials
Published
2019

12. Recent Progress in Electrode Materials for Sodium‐Ion Batteries

Author

Kim, Hyungsub, Kim, Haegyeom, Ding, Zhang, Lee, Myeong Hwan, Lim, Kyungmi, Yoon, Gabin, and Kang, Kisuk

Subjects
Affordable and Clean Energy, Macromolecular and Materials Chemistry, Materials Engineering, Interdisciplinary Engineering
Abstract

Grid-scale energy storage systems (ESSs) that can connect to sustainable energy resources have received great attention in an effort to satisfy ever-growing energy demands. Although recent advances in Li-ion battery (LIB) technology have increased the energy density to a level applicable to grid-scale ESSs, the high cost of Li and transition metals have led to a search for lower-cost battery system alternatives. Based on the abundance and accessibility of Na and its similar electrochemistry to the well-established LIB technology, Na-ion batteries (NIBs) have attracted significant attention as an ideal candidate for grid-scale ESSs. Since research on NIB chemistry resurged in 2010, various positive and negative electrode materials have been synthesized and evaluated for NIBs. Nonetheless, studies on NIB chemistry are still in their infancy compared with LIB technology, and further improvements are required in terms of energy, power density, and electrochemical stability for commercialization. Most recent progress on electrode materials for NIBs, including the discovery of new electrode materials and their Na storage mechanisms, is briefly reviewed. In addition, efforts to enhance the electrochemical properties of NIB electrode materials as well as the challenges and perspectives involving these materials are discussed.

Published
2016

25. Diagnostic performance of EUS-guided elastography for differential diagnosis of gallbladder polyp.

Author

Cho, In Rae, Lee, Sang Hyub, Choi, Jin Ho, Chun, Jung Won, Lee, Min Woo, Lee, Myeong Hwan, Kim, Junyeol, Lee, Tae Seung, Paik, Woo Hyun, Ryu, Ji Kon, and Kim, Yong-Tae

Abstract

It is difficult to differentiate between neoplastic and non-neoplastic gallbladder (GB) polyps before surgery. EUS-guided elastography (EUS-EG) is a noninvasive complementary diagnostic method. The utility of EUS-EG in the differential diagnosis of GB polyps has not been investigated. We investigated the diagnostic performance of EUS-EG for the differential diagnosis of GB polyps. Patients with GB polyps were prospectively enrolled from June 2020 until November 2022. EUS-EG and semiquantitative evaluation of the strain ratio (SR) were performed for differential diagnosis of GB polyps. Fifty-three eligible patients were divided into 2 groups based on the final diagnosis after surgery. Patient demographics, EUS characteristics, and SR values were compared. A receiver-operating characteristic curve analysis was performed to determine the optimal cutoff SR value that discriminates between neoplastic and non-neoplastic GB polyps. The median SR value for neoplastic polyps (32.93 [interquartile range {IQR}, 22.37-69.02]) was significantly higher than for non-neoplastic polyps (5.40 [IQR, 2.36-14.44], P <.001). Significant differences were found in SR values between non-neoplastic, benign neoplastic (23.38 [IQR, 13.62-39.04]), and malignant polyps (49.25 [IQR, 27.90-82.00]). The optimal cutoff SR value to differentiate between neoplastic and non-neoplastic polyps was 18.4. In multivariable logistic regression, SR value >18.4 (odds ratio, 33.604; 95% confidence interval, 2.588-436.292) was an independent predictor of neoplastic polyps. EUS-EG and SR values can be used as a supplementary method for evaluating GB polyps. (Clinical trial registration number: NCT04416763.) [ABSTRACT FROM AUTHOR]

Published
2024
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26. A Biodegradable Secondary Battery and its Biodegradation Mechanism for Eco‐Friendly Energy‐Storage Systems

Author

Lee, Myeong Hwan, primary, Lee, Jongha, additional, Jung, Sung‐Kyun, additional, Kang, Dayoung, additional, Park, Myung Soo, additional, Cha, Gi Doo, additional, Cho, Kyoung Won, additional, Song, Jun‐Hyuk, additional, Moon, Sehwan, additional, Yun, Young Soo, additional, Kim, Seok Joo, additional, Lim, Young Woon, additional, Kim, Dae‐Hyeong, additional, and Kang, Kisuk, additional

Published
2021
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27. Coupling the structure evolution and the oxygen redox electrochemistry in layered transition metal oxides

Author

Eum, Donggun, primary, Kim, Byunghoon, additional, Song, Jun-Hyuk, additional, Park, Hyeokjun, additional, Kim, Sung Joo, additional, Cho, Sung-Pyo, additional, Jang, Ho-Young, additional, Lee, Myeong Hwan, additional, Heo, Jae Hoon, additional, Ko, Youngmin, additional, Park, Sung Kwan, additional, Oh, Kyungbae, additional, Kim, Do-Hoon, additional, and Kang, Kisuk, additional

Published
2021
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29. High-Voltage Phosphate Cathodes for Rechargeable Ca-Ion Batteries

Author

Kim, Sanghyeon, primary, Yin, Liang, additional, Lee, Myeong Hwan, additional, Parajuli, Prakash, additional, Blanc, Lauren, additional, Fister, Timothy T., additional, Park, Haesun, additional, Kwon, Bob Jin, additional, Ingram, Brian J., additional, Zapol, Peter, additional, Klie, Robert F., additional, Kang, Kisuk, additional, Nazar, Linda F., additional, Lapidus, Saul H., additional, and Vaughey, John T., additional

Published
2020
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31. Toward a low-cost high-voltage sodium aqueous rechargeable battery

Author

Lee, Myeong Hwan, primary, Kim, Sung Joo, additional, Chang, Donghee, additional, Kim, Jinsoo, additional, Moon, Sehwan, additional, Oh, Kyungbae, additional, Park, Kyu-Young, additional, Seong, Won Mo, additional, Park, Hyeokjun, additional, Kwon, Giyun, additional, Lee, Byungju, additional, and Kang, Kisuk, additional

Published
2019
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32. A new ghost cancellation system for Korean GCR

Author

Kim, Ki-Bum, Oh, Jinsung, Lee, Myeong-Hwan, Hwang, Humor, and Song, Dong-Il

Subjects
Television broadcasting -- Research, Modulation (Electronics) -- Methods, Signal processing -- Research, Business, Electronics, Mass communications
Abstract

This paper describes a new ghost cancellation system built-in NTSC television based on the Korean ghost cancellation reference (KGCR) signal. The system has a highly integrated transversal filter, an unique circuit for control of the system and a highly performing algorithm for calculating the filter coefficients. Laboratory and field test results confirm that the system is effective in canceling several combination of ghosts, which exist in real situation.

Published
1994

34. A design of VSB receiver IC for digital television

Author

Oh, Ji-sung, Chang, Yong-duk, Shin, Hyun-soo, Lee, Myeong-hwan, and Kim, Ki-bum

Subjects
Digital television -- Equipment and supplies, Integrated circuits -- Design and construction, Signal processing -- Models, Decoders -- Usage, Image coding -- Methods, Business, Electronics and electrical industries, Engineering and manufacturing industries
Abstract

This paper describes a single ASIC chip that demodulates and decodes vestigial side band (VSB) digital TV signals. The VSB IC has been implemented for the receiver based on the ATSC digital TV standard[1[. It features fast digital carrier recovery and robust channel equalization. The IC is fabricated with 0.35 mu m CMOS technology with 3 metal layers. It can be applied to both modes of signal reception 8 VSB for terrestrial broadcast and 16 VSB for cable transmission.

Published
1999

38. Development of a digital FPLL ASIC for GA HDTV receivers

Author

Han, Dong-Seog, Lee, Myeong-Hwan, and Park, Kil-Houm

Subjects
Radio receivers -- Equipment and supplies, Digital loop carriers -- Design and construction, High-definition television -- Design and construction, Application-specific integrated circuits -- Product development, Digital-to-analog converters -- Design and construction, Business, Electronics and electrical industries, Engineering and manufacturing industries
Published
1997

39. Hybrid LCD panel system and its color coding algorithm

Author

Lee, Myeong-Hwan, Ko, Han-Il, and Song, Dong-Il

Subjects
Liquid crystal displays -- Design and construction, Electron optics -- Analysis, Color -- Analysis, Business, Electronics and electrical industries, Engineering and manufacturing industries
Abstract

A color liquid crystal display (LCD) panel typically used in consumer product is composed of R, G, and B subpixels. Due to the subpixel structure and color microfilters, single LCD panel system (SLPS) using such type panel has low resolution, low brightness, and poor appearance of individual color pixel elements. These problems are solved by having three LCD panel system (TLPS) which is composed of three black/white (B/W) LCD panels. However, this system requires high cost and high hardware (H/W) complexity. In this paper, we propose a new LCD system using B/W and color LCD panels called hybrid LCD panel system (HLPS) to overcome the drawbacks of other types of LCD panel applications. Also, the associated color coding algorithm for maximizing the effect of the proposed system is developed. In spite of using the simplified H/W structure, little visual difference has been attained in comparison with TLPS in the view point of resolution and brightness. And the color fidelity is better than SLPS. Among the three types of the LCD projector, the light utilization efficiency of HLPS is the highest one turned out to be as 7.34%. Also, the HLPS is compact and relatively inexpensive. Keywords: LCD, hybrid panel, HLPS, color coding, projector, optical superposition.

Published
1997

40. A new algorithm for interlaced to progressive scan conversion based on directional correlations and its IC design

Author

Lee, Myeong-Hwan, Kim, Jeong-Hoon, Lee, Jeong-Sang, Ryu, Kyeong-Keol, and Song, Dong-Il

Subjects
Image processing -- Methods, Signal processing -- Methods, Television -- Innovations, Business, Electronics and electrical industries, Engineering and manufacturing industries
Abstract

It is well known that current TV systems are suffering from uncomfortable visual artifacts such as an edge flicker, an interline flicker and a line crawling, due to the inherent nature of the interlaced scanning process. Besides, the increasing demands of large TV screens recently have turned the problem of reducing visible line structures in a TV screen into an important issue. To lessen the visual affects of those artifacts, a technique known as an interlaced to progressive conversion (IPC) technique has been widely studied in various shapes. In this paper, we propose a new algorithm for interlaced to progressive conversion, referred to as a directional correlation dependent interpolation filtering (DIF) algorithm, which is composed of a correlation-dependent linear interpolation for a signal in the low horizontal frequency band and a line doubling method for a signal lied in the high horizontal frequency band. In essence, the DIF algorithm splits the horizontal frequency band of a given input 2-Dimensional signal into two adjoint signals and apply two isolated interpolation schemes for the respective bands. In the algorithm, we develop a directional correlation dependent interpolation technique depending on the spatial correlations between the spatially symmetric samples in the observation sliding window centered at the sample to be estimated. Computer simulations and the hardware implementation of the proposed algorithm to evaluate its performance are also rigorously evaluated. To be specific, we design a chip for Luminance/Chorominance Interpolation with Peaking process (YCIP) which has been tested with a real sequence of LDP images. Simulation results validate the effectiveness of the proposed algorithm and the high performance of the YCIP in the proposed problem.

Published
1994

47. Unveiling the Intrinsic Cycle Reversibility of a LiCoO2Electrode at 4.8-V Cutoff Voltage through Subtractive Surface Modification for Lithium-Ion Batteries

Author

Seong, Won Mo, Yoon, Kyungho, Lee, Myeong Hwan, Jung, Sung-Kyun, and Kang, Kisuk

Abstract

The thermodynamic instability of the LiCoO2layered structure at >0.5Li extraction has been considered an obstacle for the reversible utilization of its near theoretical capacity at high cutoff voltage (>4.6 V vs Li/Li+) in lithium-ion batteries. Many previous studies have focused on resolving this issue by surface modification of LiCoO2, which has proven to be effective in suppressing phase transformation. To determine the extent to which surface protection of LiCoO2is effective despite its thermodynamic instability and presumably incomplete reversibility involving the O1 phase, here we verify the intrinsic reversibility of bulk LiCoO2with extended lithium extraction by ruling out the effect of a surface. Specifically, first, we show that, contrary to conventional belief, electrochemical cycling of LiCoO2at a cutoff voltage of 4.8 V (vs Li/Li+) results in better cycle stability and lower polarizations than those at 4.6 V. We demonstrate, using an exhaustive suite of characterization tools, that the rapid cycle degradation under high-voltage cycling is mostly caused by the formation of a surface resistive layer; however, these damaged surfaces are leached out faster than they are accumulated above a certain potential, which results in superior cyclability compared with that achieved for less oxidative 4.6-V cycling. This beneficial leaching out of the resistive surface layer serves as a “subtractive” surface modification and plays a role in enhancing the cycle stability and is distinguished from conventional “additive” surface modification such as coating. This approach allows us to decouple factors of the bulk and surface degradations that contribute to the capacity fade and leads to the finding that, in the absence of a resistive surface, the capacity retention of a LiCoO2electrode with 4.8-V cutoff cycling can be intrinsically high, indicating that the instability of the crystalline LixCoO2(x< 0.5) has a limited effect on the cycle stability. Our findings also explain why the strategy of coating foreign materials on the surface of LiCoO2can improve the high-voltage cycling to some extent despite the expected thermodynamic instability of the highly charged phase.

Published
2018
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