• 한국전기전자재료학회논문지
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• 제27권6호
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• pp.399-406
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• 2014

Thermal batteries are used for military power sources that require robustness and long storage life such as missiles and torpedoes. $FeS_2$ powder is currently used for cathode materials because of its high specific energy density, environmental non-toxicity and low cost. However, large particle size of conventional $FeS_2$ has been deterred its possible application for higher power thermal batteries. In order to improve the power density, high energy ball milling of $FeS_2$ has been introduced to crush the micron-sized $FeS_2$. Discharge characteristics of the single cells fabricated with nano-materials and conventional $FeS_2$ powder were evaluated.

• 전기화학회지
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• 제15권2호
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• pp.95-100
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• 2012

올리빈 구조를 가지는 $LiFePO_4$ 양극활물질은 낮은 가격과 안정성으로 인해 리튬 이차전지 시장에서 큰 관심을 받고 있다. 그러나 낮은 이온 전도도와 작동전압 때문에 상업적으로 이용되기엔 사용분야의 응용에 제한이 있다. 이러한 문제를 해결하기 위해서 철 양이온을 망간 양이온과 같은 전이금속으로 치환함으로써 작동전압을 높이는 연구가 시행되고 있다. 또한 미세구조의 나노화를 통해 리튬 이온의 확산거리를 짧게 만들어 줌으로써 이온 전도도를 높여주는 연구도 진행 중이다. 그래서 이번 연구에서는 이온의 확산거리를 짧게 만들어 주기 위해 표면적을 넓힐 수 있는 전기방사를 이용해 물질을 합성하였고, 이를 확인하기 위하여 시차주사현미경 관측을 통해 균일한 나노 섬유의 형성을 확인하였다. 또한 결정구조를 관찰하기 위해 X-선 회절 분석을 하였는데, 다른 상의 관찰 없이 단일상의 결정구조를 얻음을 확인하였다. 전기화학적 성능 확인방법으로는 충방전 테스트기를 이용하여 초기 충방전 곡선을 분석하였고, 계면저항 및 리튬 양이온의 확산을 알아보기 위해 임피던스 측정을 실행하였다.

• 한국세라믹학회지
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• 제44권6호
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• pp.297-302
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• 2007

With aids of square wave voltammetry (SWV) the redox behavior for various combination of polyvalent ions (Sb+Fe, Sb+Zn, Sb+Ce+Ti+Zn) was investigated in alkali-alkaline earth-silica CRT (Cathode Ray Tube) glass melts. The current-potential curve so called voltammogram was produced at temperature range of 1400 to $1000^{\circ}C$ under the scanned potential between 0 and -800 mV at 100 Hz. In the case of the Sb+Fe and Sb+Zn doped melts, peak for $Sb^{3+}/Sb^0$ shown voltammogram was shifted to negative direction comparing to the only Sb doped melts. However, according to voltammogram of Sb+Ce+Ti+Zn doped melt, Ti and Ce except Zn had hardly any influence on the redox reaction of Sb. Based on the temperature dependence of the peak potential, standard enthalpy (${\Delta}H^0$) and standard entropy (${\Delta}S^0$) for the reduction of $Fe^{3+}$ to $Fe^{2+}$, $Sb^{3+}$ to $Sb^0$, $Zn^{2+}$ to $Zn^0$ and $Ti^{2+}$ to $Ti^0$ in each polyvalent ion combination of CRT glass melts were calculated.

• 한국세라믹학회지
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• 제41권1호
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• pp.86-91
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• 2004

기계 화학법에 의해서 70-300nm 수준의 입도 분포를 갖는 $LiCoO_2$ 양극 분말을 제작하였다. $K_2SO_4$에 의하여 코팅 된 Li-Co 전구체는 약 $800^{\circ}C$에서 고온상 $LiCoO_2$로 결정화 되었으며, 이때 이 온도까지는 열분해 또는 서로 반응을 하지 않는 $K_2SO_4$의 영향에 의하여 분말의 입성장이 억제되어 나노 크기에 접근하는 입자를 얻을 수 있었고, 상대적으로 큰 표면 에너지에 기인하여 입자의 모양이 구형에 가깝게 형성되어 졌다. 합성돤 분말은 상용화 분말과 동일한 결정특성을 보였으나 , 투과전자현미경의 회절패턴 분석결과, 층상 뿐 아니라 부분적으로 정방정의 $LiCoO_2$ 상을 갖는 것으로 나타났다. 이러한 정방정은 주로 입자 표면에 존재하게 되어 Li의 확산을 용이하지 않게 하므로, 합성된 $LiCoO_2$ 분말은 그 크기가 나노에 접근함에도 불구하고 전체 용량 및 rate 용량이 상용화 분할보다 더 낮은 값을 보였다. 이상의 결과로부터 뛰어난 고출력 및 고성능의 전지 제작을 위하여 분말의 크기를 미세화하는 작업은 물론 입자 표면의 결정상이 잘 조절된 분말을 사용하는 것이 바람직함을 알 수 있다.

• 전기화학회지
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• 제9권1호
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• pp.6-9
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• 2006

The effect of $ZrO_2$-coating on the electrochemical properties of the cathode material $LiNi_{0.8}Co_{0.2}O_2$ was investigated using EPMA, TEM, and EIS. In particular, we facused on the distribution of the $ZrO_2$ on the particle surface to study the relation between electrochemical properties of the coated cathode and the distribution of the coating materials in the particle. Based on the results from the composition analysis and electrochemical tests, it was found that the coating layer consisted of nano-sized $ZrO_2$ particles attached non-uniformly on the particle surface and the $ZrO_2$ layer significantly improved the electrochemical properties of the cathode by suppressing the impedance growth at the interface between the electrodes and the electrolyte.

• 한국표면공학회지
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• 제39권6호
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• pp.302-311
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• 2006

Nowadays the open-type lead-acid battery for vehicle use is being replaced with the sealed-type because it needs no maintenance and has a longer cycle life. Thus researches on this battery are being conducted very actively by many advanced battery companies. There is, however, a serious problem with the maintenance free(MF) battery that its cathode electrode has a limited cycle life due to a corrosion of grid. In this study, it was aimed to improve a corrosion resistance of the cathode grid which is commonly made of Pb-Ca alloy for a mechanical strength. For this purpose, various amounts of alloying elements such as Sn, Ag and Ba were added singly or together to the Pb-Ca alloys and investigated their corrosion behaviors. Batteries fabricated by using these alloys as cathode grids were subjected to life cycle test and their corrosion layers appeared at the interface between the grids and the active materials were carefully observed in order to clarify effects of alloying elements.

• 전기화학회지
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• 제6권4호
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• pp.266-270
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• 2003

우수한 전기화학적 특성을 갖는 $LiN_{0.8}Co_{0.2}O_2$ 정극 활물질을 평균 $1{\mu}m$ 이하의 균일한 입자 분포를 얻을 수 있는 액상 반응법의 하나인 졸겔법을 이용하여 제조하였다. 제조된 $LiN_{0.8}Co_{0.2}O_2$를 X선 회절과 TEM(transmission electron microscopy)분석을 통하여 미세구조를 분석하였다. 충방전 실험전과 실험후의 미세구조의 변화에 중점을 주어 실험하였으며, 그 결과 졸겔법으로 제조된$LiN_{0.8}Co_{0.2}O_2$ 정극 활물질은 높은 가역 용량을 가지며 뛰어난 싸이클 특성을 가지고 있다 이는 졸겔법으로 제소함으로 인하여 Ni과 Co양이온의 균일한 화학조성을 가지고 있기 때문이라 생각된다. 특히 $LiCoO_2$에서 관찰되었던 cubic spinel disordering과 심각한 구조적 결함이 관찰되지 않았다. 또한 Al 치환으로 인하여 싸이클 특성을 좋아졌지만 용량은 감소하였다.

• 한국전기전자재료학회논문지
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• 제37권3호
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• pp.309-313
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• 2024

The key to determining the lifetime of OLED device is how much brightness can be maintained. It can be said that there are internal and external causes for the degradation of OLED devices. The most important cause of internal degradation is bonding and degradation in the excited state due to the electrochemical instability of organic materials. The structure of OLED modeled in this paper consists of a cathode layer, electron injection layer (EIL), electron transport layer (ETL), light emission layer, hole transport layer (HTL), hole injection layer (HIL), and anode layer on a glass substrate from top to bottom. It was confirmed that the temperature generated in OLED was distributed around the maximum of 343.15 K centered on the emission layer. It can be seen that the heat distribution generated in the presented OLED structure has an asymmetrically high temperature distribution toward the cathode, which is believed to be because the sizes of the cathode and positive electrode are asymmetric. Therefore, when designing OLED, it is believed that designing the structures of the cathode and anode electrodes as symmetrically as possible can ensure uniform heat distribution, maintain uniform luminance of OLED, and extend the lifetime. The thermal distribution of OLED was analyzed using the finite element method according to Comsol 5.2.

• Tribology and Lubricants
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• 제20권5호
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• pp.237-244
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• 2004

Micro/nano tribological characteristics of PTFE coating films were experimentally studied. PTFE (polytetrafluoroethylene) modified polyethylene and low molecular weight PTFE were used as a coating materials. These films were deposited on Si-wafer (100) by IBAD (ion beam assisted deposition) method. The Ar ion beam sputtering was performed to change the surface topography of films using a hollow cathode ion gun under different Ar ion dose conditions in a vacuum chamber. Micro/nano tribological characteristics, water wetting angles and roughness were measured with a micro tribotester, SPM (scanning probe microscope), contact anglemeter and profilometer, respectively. The durability of the films were measured with macro tribotester. Results showed that the PTFE coating surfaces were converted to hydrophobic. The water contact angle of coated surfaces and surface roughness increased with the coating thickness. Adhesion and friction in micro and nano scale were governed by magnitude of normal load in soft material such as PTFE films. As the increase of sputtering time on low molecular weight PTFE films, the surface roughness was increased and nano adhesion and friction were decreased. The nano tribological characteristics of surfaces are mainly improved by chemical modification such as PTFE coating and given a synergy effect by the physical modification such as topographic modification.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2011년도 제40회 동계학술대회 초록집
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• pp.54-54
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• 2011

The demand for low-friction, wear and corrosion resistant components, which operate under severe conditions, has directed attentions to advanced surface engineering technologies. The Filtered Vacuum Arc Cathode Deposition (FVACD) process has demonstrated atomically smooth surface at relatively high deposition rates over large surface areas. Preparation of Ti-Si-C-N nanocomposite coatings on (100) Si and stainless steel substrates with tetramethylsilane (TMS) gas pressures to optimize the film preparation conditions. Ti-S-C-N coatings were characterized using X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy, nanoindentation, Rockwell C indentation and ball-on-disk wear tests. The XRD results have confirmed phase formation information of TiSiCN coatings, which shows mixing of TiN and TiC structure, corresponding to (111), (200) and (220) planes of TiCN. The chemical composition of the film was investigated by XPS core level spectra. The binding energy of the elements present in the films was estimated using XPS measurements and it shows present of elemental information corresponding to Ti2p, N1s, Si 2p and C1. Film hardness and elastic modulus were measured with a nano-indenter, and film hardness reached 40 GPa. Tribological behaviors of the films were evaluated using a ball-on-disk tribometer, and the films demonstrated properties of low-friction and good wear resistance.