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Jou-Hyeon Ahn

Bio: Jou-Hyeon Ahn is an academic researcher from Gyeongsang National University. The author has contributed to research in topics: Lithium & Electrolyte. The author has an hindex of 50, co-authored 276 publications receiving 7888 citations.


Papers
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TL;DR: In this paper, Davankov-type hyper-crosslinked resin beads have been synthesized using gel-type and permanently porous poly(divinylbenzene-co-vinylbenzyl chloride) (DVB−VBC) precursor resins without any external electrophile.
Abstract: Synthesis of Davankov-type hyper-cross-linked resin beads has been carried out using gel-type and permanently porous poly(divinylbenzene-co-vinylbenzyl chloride) (DVB−VBC) precursor resins without any external electrophile. Of the Lewis acids examined (FeCl3, AlCl3, SnCl4), FeCl3 was by far the most effective catalyst. Rather remarkably in the case of a gel-type 2 mol % DVB−VBC precursor, extensive microporosity was generated within only 15 min of initiating the cross-linking reaction, yielding a surface area (N2 sorption/BET) of ∼1200 m2 g-1, which rose steadily to a maximum approaching 2000 m2 g-1 after 18 h. In the case of porous DVB−VBC precursor resins, the presence of discrete pores in the precursor, accompanied by a micropore fraction on hyper-cross-linking, yields resins with a clearly bimodal distribution of pores. Manipulation of the Friedel−Crafts reaction variables and the structure of the precursor resin allows final resin products to be prepared with surface areas in the range ∼300−2000 m2 g-1.

272 citations

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TL;DR: In this paper, the suitability of some single/binary liquid electrolytes and polymer electrolytes with a 1M solution of LiCF3SO3 was evaluated for discharge capacity and cycle performance of Li/S cells at room temperature.

246 citations

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TL;DR: In this article, a Na/MoS2 cell was assembled so as to evaluate its electrochemical properties as a rechargeable battery, which showed two characteristic plateaus at 0.93 and 0.8 V at different discharge depths.

215 citations

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TL;DR: In this paper, the capacity of carbon-coated sulfur cells was investigated and a discharge reaction mechanism of lithium/sulfur cells was suggested. But, the results were limited to the first discharge cycle.

200 citations

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TL;DR: In this paper, a solid-state sodium/sulfur battery using polyvinylidene-fluoride-hexafluoropropene (PVDF) polymer electrolyte was prepared and tested at room temperature.
Abstract: Solid-state sodium/sulfur batteries using polyvinylidene-fluoride-hexafluoropropene (PVDF) polymer electrolyte were prepared and tested at room temperature. Solid sodium/sulfur batteries may be composed of solid-composite-type sulfur electrodes, sodium metal electrodes, and PVDF gel polymer electrolyte. The PVDF gel polymer electrolyte with tetraglyme plasticizer and NaCF 3 SO 3 salt had a high sodium ion conductivity of 5.1 X 10 -4 S cm -1 at 25°C. During the first discharge, the sodium/sulfur battery showed two plateau potentials of 2.27 and 1.73 V, respectively. The first discharge capacity was 489 mAh/g sulfur at room temperature, which was similar to the high temperature battery. The discharge capacity drastically decreased by repeated charge-discharge cycling, and remained at 40 mAh/g after 20 cycles.

180 citations


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08 Dec 2001-BMJ
TL;DR: There is, I think, something ethereal about i —the square root of minus one, which seems an odd beast at that time—an intruder hovering on the edge of reality.
Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

33,785 citations

Journal ArticleDOI
TL;DR: The energy that can be stored in Li-air and Li-S cells is compared with Li-ion; the operation of the cells is discussed, as are the significant hurdles that will have to be overcome if such batteries are to succeed.
Abstract: Li-ion batteries have transformed portable electronics and will play a key role in the electrification of transport. However, the highest energy storage possible for Li-ion batteries is insufficient for the long-term needs of society, for example, extended-range electric vehicles. To go beyond the horizon of Li-ion batteries is a formidable challenge; there are few options. Here we consider two: Li-air (O(2)) and Li-S. The energy that can be stored in Li-air (based on aqueous or non-aqueous electrolytes) and Li-S cells is compared with Li-ion; the operation of the cells is discussed, as are the significant hurdles that will have to be overcome if such batteries are to succeed. Fundamental scientific advances in understanding the reactions occurring in the cells as well as new materials are key to overcoming these obstacles. The potential benefits of Li-air and Li-S justify the continued research effort that will be needed.

7,895 citations

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TL;DR: In this paper, the authors report the feasibility to approach such capacities by creating highly ordered interwoven composites, where conductive mesoporous carbon framework precisely constrains sulphur nanofiller growth within its channels and generates essential electrical contact to the insulating sulphur.
Abstract: The Li-S battery has been under intense scrutiny for over two decades, as it offers the possibility of high gravimetric capacities and theoretical energy densities ranging up to a factor of five beyond conventional Li-ion systems. Herein, we report the feasibility to approach such capacities by creating highly ordered interwoven composites. The conductive mesoporous carbon framework precisely constrains sulphur nanofiller growth within its channels and generates essential electrical contact to the insulating sulphur. The structure provides access to Li+ ingress/egress for reactivity with the sulphur, and we speculate that the kinetic inhibition to diffusion within the framework and the sorption properties of the carbon aid in trapping the polysulphides formed during redox. Polymer modification of the carbon surface further provides a chemical gradient that retards diffusion of these large anions out of the electrode, thus facilitating more complete reaction. Reversible capacities up to 1,320 mA h g(-1) are attained. The assembly process is simple and broadly applicable, conceptually providing new opportunities for materials scientists for tailored design that can be extended to many different electrode materials.

5,151 citations