• Electronics and Telecommunications Trends
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• v.36 no.3
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• pp.65-75
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• 2021

In the era of the 4th industrial revolution, interest in flexible devices is increasing for information and communication technology electronic products. This is a hot technology field in which competition is intensifying to preoccupy the global market for flexible electronic devices because of the many advantages of ultra-lightweight, flexibility, design diversity, high applicability, and low cost. Some flexible electronic products have been commercialized in Korea, but they are still inadequate in terms of price versus performance, so technology development is required continuously. Particularly, the development of flexible electronic materials is emerging as a key factor for flexible electronic device applications. In this study, we will look into the flexible electronic material technology and industry trends following the trend of flexible technology changes in the display, secondary battery, and solar cell, which has emerged as national core industry and has secured global competitiveness. In addition, I want to introduce the Flexible Electronic Material Center, which was established to foster the flexible electronic material industry.

• Journal of the Korean Electrochemical Society
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• v.24 no.3
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• pp.65-75
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• 2021

Coin cell is a basic testing platform for battery research, discovering new materials and concepts, and contributing to fundamental research on next-generation batteries. Li metal batteries (LMBs) are promising since a high energy density (~500 Wh kg^-1) is deliverable far beyond Li-ion. However, Li dendrite-triggered volume fluctuation and high surface cause severe deterioration of performance. Given that such drawbacks are strongly dependent on the cell parameters and structure, such as the amount of electrolyte, Li thickness, and internal pressure, reliable Li metal coin cell testing is challenging. For the LMB-specialized coin cell testing platform, this study suggests the optimal coin cell structure that secures performance and reproducibility of LMBs under stringent conditions, such as lean electrolyte, high mass loading of NMC cathode, and thinner Li use. By controlling the cathode/anode (C/A) area ratio closer to 1.0, the inactive space was minimized, mitigating the cell degradation. The quantification and imaging of inner cell pressure elucidated that the uniformity of the pressure is a crucial matter to improving performance reliability. The LMB coin cells exhibit better cycling retention and reproducibility under higher (0.6 MPa → 2.13 MPa) and uniform (standard deviation: 0.43 → 0.16) stack pressure through the changes in internal parts and introducing a flexible polymer (PDMS) film.

• Journal of the Korean Electrochemical Society
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• v.17 no.2
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• pp.103-110
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• 2014

In the study, a room temperature ionic liquids as a co-solvent was used to evaluate the feasibility with various electrodes in Li-ion batteries. 1-Ethyl-1-methyl piperidinium bis(trifluoromethanesulfonyl) imide(PP12 TFSI) is an ionic liquid that melts at $85^{\circ}C$. Pure PP12 TFSI is not able to be used as an electrolyte because it is a solid salt at room temperature. PP12 TFSI is mixed with EC/DEC(1/1 vol.%) to prepare mixed solvents. The electrolyte 1.5M $LiPF_6$ in a mixed solvent having 44 wt.% PP12 TFSI is prepared to evaluated the various electrodes. The electrolytes provides good cycles life of cells with $LiNi_{0.5}Mn_{1.5}O_4(LNMO)$, $LiFePO_4(LFP)$, $Li_4Ti_5O_{12}(LTO)$ and artificial graphite. Further improvement of the cell performances can be accomplished by enhancing wettability of electrolytes to electrodes.

• Journal of the Korean Electrochemical Society
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• v.3 no.2
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• pp.100-103
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• 2000

Polymeric gel electrolytes based on polyacrylronitile blended with poly(vinylidene fluoride-co-hexafluoro-propylene)(P(VdF-co-HFP), which were reinforced with glass fiber cloth(GFC) to increase the mechanical strength, were prepared for the practical use in secondary battery. Test cell consisting of $LiCoO_2$ as a cathode and mesophase pich-based ca.bon fiber (MCF) as an anode material showed a capacity of 110 mAh/g based on the cathode weight at 0.2C rate at room temperature. Over $80\%$ of initial capacity was retained after 400cycles, indicating that GFC is suitable for a reinforcing material to increase the mechanical strength of gel based electrolytes.

• Journal of the Korean Electrochemical Society
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• v.18 no.2
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• pp.45-50
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• 2015

In the present work, to increase the chemical stability of the lithium-ion-conducting ceramic electrolyte ($Li_{1+x+y}Al_xTi_{2-x}Si_yP_{3-y}O_{12}$, LATP) in the strong alkaline solution, the surface of LATP was modified by the nitridation process. The surface and structural properties of nitride LATP solid electrolyte were characterized by X-ray diffraction, X-ray photoelectron spectrometer and scanning electron microscopy and ac-impedance spectroscopy, which were correlated to the chemical stability and electrochemical performance of LATP. The nitrided LATP immersed in the alkaline solution for 30 days exhibits the enhanced chemical stability than the pristine LATP. Moreover, a rechargeable hybrid Li-air battery constructed with the nitrided LATP solid electrolyte shows considerably reduced discharge-charge voltage gaps (enhanced the round-trip efficiency) in comparison to the cell constructed with pristine LATP, which indicate that the surface nitridation process can be the efficient way to improve the chemical stability of solid electrolyte in alkaline media.

• Journal of the Korean Electrochemical Society
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• v.20 no.2
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• pp.27-33
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• 2017

Conventional lithium ion batteries suffer from notorious safety issues caused by inevitable lithium dendrite formation and proliferation during over/fast charging processes. The lithium dendrites or mechanical damage on the separator induce internal short circuit in LiB that generates extensive amount of heat within contacted electrode surfaces through the separator. During this heat generation, conventional polyolefin separators shrinks dramatically, and increasing short circuit pathway, that causes the battery to explode. To overcome this serious issue, ceramic coated separators are developed in commercial LiB to enhance thermal and mechanical stability. In this paper, various size(IL = 488.5 nm, I = 538.7 nm, S = 810.3 nm, D = 1533.3 nm) of $Al_2O_3$ particles are coated using styrene-butadiene rubber(SBR) / carboxymethyl cellulose(CMC) binder on PE separator to investigate its thermal stability and electrochemical effect on LiB coin cell with NCM cathode and Li metal anode.

• Biomolecules & Therapeutics
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• v.23 no.6
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• pp.597-603
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• 2015

Synthetic cannabinoids JWH-018 and JWH-250 in 'herbal incense' also called 'spice' were first introduced in many countries. Numerous synthetic cannabinoids with similar chemical structures emerged simultaneously and suddenly. Currently there are not sufficient data on their adverse effects including neurotoxicity. There are only anecdotal reports that suggest their toxicity. In the present study, we evaluated the neurotoxicity of two synthetic cannabinoids (JWH-081 and JWH-210) through observation of various behavioral changes and analysis of histopathological changes using experimental mice with various doses (0.1, 1, 5 mg/kg). In functional observation battery (FOB) test, animals treated with 5 mg/kg of JWH-081 or JWH-210 showed traction and tremor. Their locomotor activities and rotarod retention time were significantly (p<0.05) decreased. However, no significant change was observed in learning or memory function. In histopathological analysis, neural cells of the animals treated with the high dose (5 mg/kg) of JWH-081 or JWH-210 showed distorted nuclei and nucleus membranes in the core shell of nucleus accumbens, suggesting neurotoxicity. Our results suggest that JWH-081 and JWH-210 may be neurotoxic substances through changing neuronal cell damages, especially in the core shell part of nucleus accumbens. To confirm our findings, further studies are needed in the future.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.681-682
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• 2013

전기는 우리 주변의 에너지 형태 중에서 가장 편리하고 광범위하게 사용되고 있다. 이러한 전기는 전자제품, 전기자동차, 에너지 저장 플랜트 등 매우 많은 분야에서 저장되고 사용되고 있다. 특히 에너지 저장 용량의 확대는 휴대폰, 노트북 PC 등 휴대용 IT 기기의 성장에 결정적인 역할을 하였다. 가볍고 작으면서도 고용량의 전기 에너지 저장 장치가 없었다면, 통신이나 인터넷 그리고 오락 등 다양한 기능을 작은 휴대용 기기에 구현할 수 없었을 것이다. 그러나 시간이 흐를수록 기기의 요구 성능이 높아지고 소비자의 니즈가 더욱더 다양해지고 고도화될수록 단일 부품으로 가장 큰 부피를 차지하는 에너지 저장 장치의 용량과 디자인은 점점 중요해지고 있다. 이러한 에너지 저장 장치에서 가장 친숙한 형태는 2차 전지 계열이다. 납 축전지를 비롯하여, 니켈수소, 니켈카드뮴, electrochemical capacitor와 Li ion 계열 등이 대표적이다. 특히 Li ion 배터리는 모바일, 자동차 및 에너지 저장 그리드 등과 같은 다양한 분야에 가장 많이 적용되고있다. Li ion 배터리에 대하여 현재의 핵심적인 연구분야는 전극 재료(cathode, anode)와 electrolyte에 대한 것이다. Anode 전극 재료 중에서 가장 많이 사용되는 재료는 카본을 기반으로 하는 재료로 안정성에 대한 장점이 있지만 에너지 밀도가 낮다는 단점이 있다. 에너지 저장 용량 증가에 대한 필요성이 증가하기 때문에 현재 많이 사용되고 있는 에너지 밀도가 낮은 카본 재료를 대체하기 위해서 이론 용량이 높다고 알려진 실리콘과 같은 메탈이나 주석 산화물과 같은 천이 금속 산화물에 대하여 많은 연구가 진행되고 있다. 특히 현재까지 알려진 많은 재료 중에서 가장 큰 capacity (~4,000 mAh/g)를 가지고 있다고 알려진 실리콘이 카본의 대체 재료로 많은 연구가 진행되고 있다. 그러나, Li 과 반응을 하며 약 300~400%에 달하는 부피팽창이 발생하고, 이러한 부피 팽창 때문에 충 방전이 진행됨에 따라 current collector로부터 박리되는 현상을 보여 빠른 용량 감소를 보여주고 있다. 본 연구에서는 adhesion layer를 current collector와 실리콘 전극 재료 사이에 삽입하여 충 방전 시 부피팽창에 의한 미세구조의 변화와 electrochemical 특성에 대한 영향을 알아보았다. 실험에 사용한 anode 전극은 상용 Cu foil current collector에 RF/DC magnetron 스퍼터링을 통해 다양한 종류(Ti, Ta 등)의 adhesion layer과 200 nm 두께의 Si 박막을 증착하였다. 또한 Bio-logic Potentiostat/ Galvanostat VMP3 와 WanAtech automatic battery cycler 장비를 사용하여 0.2 C-rate로 half-cell 타입의 코인 셀로 조립한 전극에 대한 충 방전 실험을 진행하였다. Adhesion layer의 사용으로 인해 실리콘 박막과 Cu current collector 사이의 박리 현상을 줄여줄 수 있었고, 충 방전 시 Cu 원자의 실리콘 박막으로의 확산을 통한 brittle한 Cu-Si alloy 형성을 막아 줄 수 있어 큰 특성 향상을 확인할 수 있었다. 또한, 리튬과 실리콘의 반응을 통한 형태와 미세구조 변화를 SEM, TEM 등의 다양한 장비를 사용하여 확인하였고, 이를 통해 adhesion layer의 사용이 전극의 특성향상에 큰 영향을 끼쳤다는 것을 확인할 수 있었다.

• Korean Chemical Engineering Research
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• v.55 no.3
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• pp.307-312
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• 2017

In this study, the electrochemical performance of surface modified carbon using the PFO (pyrolyzed fuel oil) was investigated by chemical activation with KOH and $K_2CO_3$. PFO was heat treated at $390{\sim}400^{\circ}C$ for 1~3h to prepared the pitch. Three carbon precursors (pitch) prepared by the thermal reaction were 3903 (at $390^{\circ}C$ for 3h), 4001(at $400^{\circ}C$ for 1h) and 4002 (at $400^{\circ}C$ for 2h). Also, the effect of chemical activation catalysts and mixing time on the development of porosity during carbonization was investigated. The prepared carbon was analyzed by BET and FE-SEM. It was shown that chemical activation with KOH could be successfully used to develop carbon with specific surface area ($3.12m^2/g$) and mean pore size (22 nm). The electrochemical characteristics of modified carbon as the anode were investigated by constant current charge/discharge, cyclic voltammetry and electrochemical impedance tests. The coin cell using pitch (4002) modified by KOH has better initial capacity (318 mAh/g) than that of other pitch coin cells. Also, this prepared carbon anode appeared a high initial efficiency of 80% and the retention rate capability of 2C/0.1 C was 92%. It is found that modified carbon anode showed improved cycling and rate capacity performance.

• Journal of the Korean Electrochemical Society
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• v.19 no.1
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• pp.21-27
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• 2016

Vanadium redox flow batteries (VRFBs) using the electrolytes containing various vanadium ions in sulfuric acid as supporting solution are one of the energy storage devices in alternatively charging and discharging operation modes. The positive electrolyte contains $V^{5+}/V^{4+}$ and the negative electrolyte $V^{2+}/V^{3+}$ depending on the operation mode. To prevent the mixing of two solutions, proton exchange membranes are mainly used in VRFBs. Nafion 117 could be the most promising candidate due to the strong oxidative property of $V^{5+}$ ion, but causes high crossover of electroactive species to result in a decrease in coulombic efficiency. In this study, the composite membranes using Nafion ionomer and porous polyethylene substrate were prepared to keep good chemical stability and to decrease the cost of membranes, and were compared to the properties and performance of the commercially available electrolyte membrane, Nafion 117. As a result, the water uptake and ionic conductivity of the composite membranes increased as the thickness of the composite membranes increased, but those of Nafion 117 slightly decreased. The permeability of vanadium ions for the composite membranes significantly decreased compared to that for Nafion 117. In a single cell test for the composite membranes, the voltage efficiency decreased and the coulombic efficiency increased, finally resulting in the similar energy efficiency. In conclusion, the less cost of the composite membranes by decreasing 6.4 wt.% of the amount of perfluorinated sulfonic acid polymer due to the introduction of porous substrate and lower vanadium ion permeability to decrease self-discharge were achieved than Nafion 117.