• Korean Chemical Engineering Research
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• 제52권1호
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• pp.52-57
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• 2014

본 연구에서는 낮은 사이클 안정성을 갖는 MCMB의 단점을 향상시키기 위하여 높은 사이클 안정성과 부피팽창이 없는 장점을 갖는 물질인 $Li_4Ti_5O_{12}$를 코팅하여 core-shell 구조의 $MCMB/Li_4Ti_5O_{12}$를 합성하고 $MCMB/Li_4Ti_5O_{12}$를 음극으로, $LiMn_2O_4$, Active carbon fiber를 양극으로 사용하여 단위 셀을 제조하였다. $LiPF_6$ 염과 EC/DMC/EMC 용매를 전해질로 사용하여 제조한 하이브리드 커패시터 단위 셀로 충방전, 사이클, 순환전압전류, 임피던스 테스트를 진행하여 전기화학적 특성을 평가한 결과, MCMB-$Li_4Ti_5O_{12}/LiMn_2O_4$ 전극을 사용한 하이브리드 커패시터가 MCMB 전극의 하이브리드 커패시터 보다 좋은 충/방전 성능을 보였고, 67 Wh/kg, 781 W/kg의 에너지밀도와 출력밀도를 나타내었다.

• 한국재료학회지
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• 제28권5호
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• pp.273-278
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• 2018

Lithium-ion batteries have been considered the most important devices to power mobile or small-sized devices due to their high energy density. $LixCoO_2$ has been studied as a cathode material for the Li-ion battery. However, the limitation of its capacity impedes the development of high capacity cathode materials with Ni, Mn, etc. in them. The substitution of Mn and Ni for Co leads to the formation of solid solution phase $LiNi_xMn_yCo_{1-x-y}O_2$ (NMC, both x and y < 1), which shows better battery performance than unsubstituted $LiCoO_2$. However, despite a high discharge capacity in the Ni-rich compound (Ni > 0.8 in the metal site), poor cycle retention capability still remains to be overcome. In this study, aiming to improve the stability of the physical and chemical bonding, we investigate the stabilization effect of Ca in the Ni-rich layered compound $Li(Ni_{0.83}Co_{0.12}Mn_{0.05})O_2$, and then Ca is added to the modified secondary particles to lower the degree of cationic mixing of the final particles. For the optimization of the final grains added with Ca, the Ca content (x = 0, 2.5, 5.0, 10.0 at.%) versus Li is analyzed.

• Carbon letters
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• 제16권2호
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• pp.78-85
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• 2015

Activated carbons (ACs) were prepared by activation of coal tar pitch (CTP) in the range of $700^{\circ}C-1000^{\circ}C$ for 1-4 h using potassium hydroxide (KOH) powder as the activation agent. The optimal activation conditions were determined to be a CTP/KOH ratio of 1:4, activation temperature of $900^{\circ}C$, and activation time of 3 h. The obtained ACs showed increased pore size distribution in the range of 1 to 2 nm and the highest specific capacitance of 122 F/g in a two-electrode system with an organic electrolyte, as measured by a charge-discharge method in the voltage range of 0-2.7 V. In order to improve the performance of the electric double-layer capacitor electrode, various mixtures of CTP and petroleum pitch (PP) were activated at the optimal activation conditions previously determined for CTP. Although the specific capacitance of AC electrodes prepared from CTP only and the mixtures of CTP and PP was not significantly different at a current density of 1 A/g, the AC electrodes from CTP and PP mixtures showed outstanding specific capacitance at higher current rates. In particular, CTP-PP61 (6:1 mixture) had the highest specific capacitance of 132 F/g, and the specific capacitance remained above 90% at a high current density of 3 A/g. It was found that the high specific capacitance could be attributed to the increased micro-pore volume of ACs with pore sizes from 1 to 2 nm, and the high power density could be attributed to the increased meso-pore volume.

• 한국재료학회:학술대회논문집
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• 한국재료학회 2012년도 춘계학술발표대회
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• pp.73-73
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• 2012

Modern technology-driven society largely relies on hybrid electric vehicles or electric vehicles for eco-friendly transportation and the use of high technology devices. Lithium rechargeable batteries are the most promising power sources because of its high energy density but still have a challenge. Graphite is the most widely used anode material in the field of lithium rechargeable batteries due to its many advantages such as good cyclic performances, and high charge/discharge efficiency in the initial cycle. However, it has an important safety issue associated with the dendritic lithium growth on the anode surface at high charging current because the conventional graphite approaches almost 0 V vs $Li/Li^+$ at the end of lithium insertion. Therefore, a fundamental solution is to use an electrochemical redox couple with higher equilibrium potentials, which suppresses lithium metal formation on the anode surface. Among the candidates, $Li_4Ti_5O_{12}$ is a very interesting intercalation compound with safe operation, high rate capability, no volume change, and excellent cycleability. But the insulating character of $Li_4Ti_5O_{12}$ has raised concerns about its electrochemical performance. The initial insulating character associated with Ti4+ in $Li_4Ti_5O_{12}$ limits the electronic transfer between particles and to the external circuit, thereby worsening its high rate performance. In order to overcome these weak points, several alternative synthetic methods are highly required. Hence, in this presentation, novel ways using a synergetic strategy based on 1D architecture and surface coating will be introduced to enhance the kinetic property of Ti-based electrode. In addition, first-principle calculation will prove its significance to design Ti-based electrode for the most optimized electrochemical performance.

• 한국물환경학회지
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• 제30권4호
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• pp.394-402
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• 2014

High-voltage dielectric discharges are an emerging technique in environmental pollutant degradation, which are characterized by the production of hydroxyl radicals as the primary degradation species. The initiation and propagation of the electrical discharges depends on several physical, chemical, and electrical parameters such as 1st and 2nd voltage of power, gas supply, conductivity and pH. These parameters also influence the physical and chemical characteristics of the discharges, including the production of reactive species such as OH, $H_2O_2$ and $O_3$. The experimental results showed that the optimum 1st voltage and oxygen flow rate for RNO (N-Dimethyl-4-nitrosoaniline, indicator of the generation of OH radical) degradation were 160 V (2nd voltage of is 15 kV) and 4 L/min, respectively. As the 2nd voltage (4 kV to 15 kV) was increase, RNO degradation was increased and, generated $H_2O_2$ and $O_3$ concentration were increased. The conductivity of the solution was not influencing the RNO degradation, $H_2O_2$ and $O_3$ generation. The pH effect on RNO degradation was not high. However, the lower pH and the conductivity, the higher $H_2O_2$ and $O_3$ generation were observed.

• 대한수의학회지
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• 제49권1호
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• pp.67-71
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• 2009

A 10-year old female Yorkshire terrier with nasal discharge and swelling was referred to the local animal hospital. Abnormal mass of right nasal cavity was detected in physical examination and radiography. According to the radiographs of the head, there was an evidence of bony destruction in right nose. Oronasal fistula was detected in right maxillary canine teeth. After surgical excision, the sample of nasal mass was refereed to Pathology Department of Veterinary Medicine in Jeju National University. Grossly, the enlarged mass was soft and 3 ${\times}$ 3 cm in size. Histopathologically, the neoplastic mass was composed of tubular to tubulopapillary structures which were lined by single to 6~7 layers of cuboidal to ciliated columnar cells. These neoplastic cells showed invasive tendency to adjacent normal parenchyma. They had uniform, round to oval nuclei, cytoplasm with small vacuoles and indistinct cellular margin. The number of mitotic figures was varied in different areas, ranged from 0 to 4 per high power field. Necrotic foci and infiltration of inflammatory cells including neutrophils, lymphocytes, and plasma cells also presented in the mass. Immunohistochemically, the neoplastic cells demonstrated strong positive reaction for cytokeratin (CK) 18 but were negative for CK 7 and 8. Based on the gross, histopathology and immunohistochemistry, this mass was diagnosed as nasal adenocarcinoma originated from respiratory epithelium.

• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제54권6호
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• pp.255-261
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• 2005

Recently, the RF inductive discharge or inductively coupled plasma continues to attract growing attention as an effective plasma source in many industrial applications, the best known of which are plasma processing and lighting technology. To the point of lighting sources, the ring-shaped electrodeless fluorescent lamps utilizing an inductively coupled plasma have been objects of interest and research during the last decades, mainly because of their potential for extremely long life, high lamp efficacies, rapid power switching response. In this paper, maxwell 3D finite element analysis program (Ansoft) was used to obtain electromagnetic properties associated with the coil and nearby structures. The electromagnetic emitting properties were presented by 3D simulation software operated at 250 kHz and some specific conditions. The electromagnetic field in the ferrite core was shown to be high and symmetric. An LS-100 luminance meter and a Darsa-2000 spectrum analyzer were used in the experiment. According to data on the lamp tested using high magnetic field ferrite, the optical and thermal wave fields were shown to be high around the ring-shaped electrodeless fluorescent lamp. The optical or light field was high at the center of the bulb rather than around the ferrite core. The light conditions of the bulb were assumed to be complex, depending on the condition of the filler gas, the volume of the bulb, and the frequency of the inverter. Our results have shown coupling between the gas plasma and the field of the light emitted to be nonlinear.

• 한국철도학회논문집
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• 제18권4호
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• pp.325-334
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• 2015

본 논문에서는 하이브리드 에너지 저장장치의 계통연계 제어에 대하여 기술 하였다. 배터리는 큰 에너지 밀도를 가지지만 순간 전력밀도는 낮아 급격한 전류변동이 일어날 경우 수명이 저하된다. 이러한 단점을 보완하기 위해 수퍼커패시터를 함께 사용하는 하이브리드 에너지 저장장치를 구성하였고 이에 대한 제어방법을 제안하였다. 배터리와 수퍼커패시터의 제어를 위해서는 예측형 전류제어기를 가지는 p-q 제어방법을 적용하였다. 제안된 제어기의 효용성을 검증하기 위해 실제 계통모델에 대한 PSIM과 RTDS를 이용한 시뮬레이션을 수행하였다.

• 조명전기설비학회논문지
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• 제23권2호
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• pp.70-76
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• 2009

최근 경제적 시간적 이유로 전력기기의 운전 중 부분방전 감시진단 장치가 많이 이용되는 추세에 있으나, 시 공간적으로 다양한 종류의 잡음의 영향이 문제시되고 있다. 이에 여러가지 잡음제거 기법들이 개발되었으나 범용적이지 않고 설정이나 환경에 따라 성능이 상이하다. 본 논문에서는 부분방전 측정신호의 잡음포함 정도를 수치적으로 제시할 수 있는 방법을 제시하였다. 이 기법이 적용되어 개발된 알고리즘을 이용하여, 다수 잡음제거 기법의 설정에 따른 다양한 결과 중 최선의 결과를 자동적으로 선택할 수 있었다. 운전 중 부분방전 감시진단 시스템에 사용되는 세 가지 잡음제거 기법에 적용하여 성공적으로 복합화 하였고, 국내 다양한 잡음 환경의 고전압 기기들로부터 실측한 데이터에 능동적으로 적응한 잡음제거 결과를 도출할 수 있었다.

• 한국정보통신학회:학술대회논문집
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• 한국해양정보통신학회 2002년도 춘계종합학술대회
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• pp.529-534
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• 2002

범세계 해상 조난·안전 시스템(Global Maritime Distress ＆ Safety System： GMDSS)에 따라 DSC(Digital Selective Calling) 전용 수신기, DSC 장치, VHF 송수신기 등이 국제항해에 종사하는 300GT 이상의 모든 선박에 의무적으로 탑재하도록 규정되었다. 또한, 최근에 국제해사기구(International Maritime Organization： IMO)는 GMDSS를 포함한 항해·통신 장비에 EMC 규정을 적용하도록 권고함에 따라 현재 선박에서 사용되는 대부분의 전자가 새로운 규정에 대응해야 하는 문제점에 직면하게 되었다. 본 연구에서는 채널 70 DSC 전용 수신기, DSC 장치, VHF 송수신장치가 집적된 장치에 대하여 예상되는 EMC 규정을 미리 적용 및 분석하여 보고 대처방안을 모색하였다. 시험은 도선 및 방사를 통한 불요파의 측정과 같은 전자파 간섭을 비롯하여 전압, 주파수 변위에 대한 내성과 정전기 방전에 대한 내성을 포함한 다양한 전자파 감응성 시험 등이 적용되었고 이에 따른 국내외 제품의 전원 및 접지에 대한 문제점을 파악할 수 있게 되었다.