• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.27 no.6
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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.

• Journal of the Korean Electrochemical Society
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• v.15 no.2
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• pp.95-100
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• 2012

$LiFePO_4$ is an attractive cathode material due to its low cost, good cyclability and safety. But it has low ionic conductivity and working voltage impose a limitation on its application for commercial products. In order to solve these problems, the iron($Fe^{2+}$)site in $LiFePO_4$ can be substituted with other transition metal ions such as $Mn^{2+}$ in pursuance of increase the working voltage. Also, reducing the size of electrode materials to nanometer scale can improve the power density because of a larger electrode-electrolyte contact area and shorter diffusion lengths for Li ions in crystals. Therefore, we chose electrospinning as a general method to prepare $Li[Fe_{0.9}Mn_{0.1}]PO_4$ to increase the surface area. Also, there have been very a few reports on the synthesis of cathode materials by electrospinning method for Lithium ion batteries. The morphology and nanostructure of the obtained $Li[Fe_{0.9}Mn_{0.1}]PO_4$ nanofibers were characterized using scanning electron microscopy(SEM). X-ray diffraction(XRD) measurements were also carried out in order to determine the structure of $Li[Fe_{0.9}Mn_{0.1}]PO_4$ nanofibers. Electrochemical properties of $Li[Fe_{0.9}Mn_{0.1}]PO_4$ were investigated with charge/discharge measurements, electrochemical impedance spectroscopy measurements(EIS).

• Journal of the Korean Ceramic Society
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• v.44 no.6 s.301
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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.

• Journal of the Korean Ceramic Society
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• v.41 no.1
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• pp.86-91
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• 2004

$LiCoO_2$ cathode powders with round particle shaped and nano grain sized of 70-300nm were synthesized by a mechanochemical method. The surface of Li-Co precursor prepared by freeze drying method was modified by $K_2SO_4$ coating and ball milling was used for the coating process. The precursor was crystallized to high temperature form of $LiCoO_2$ at $800^{\circ}C$ and the grain growth was inhibited by the $K_2SO_4$ coating effect. The $K_2SO_4$ coating was not decomposed at $800^{\circ}C$ and prevented the contact in the Li-Co precursor particles. The nano-sized $LiCoO_2$ powder had tetragonal phase and it affected the Li diffusion through the surface of particles. It means that the anode materials for hight performance battery should be satisfied not only small particle size but phase contol on the surface of particles. In this study, the powder characteristics and rate capabilities were compared with a commercial powder and the nano-sized $LiCoO_2$ powder fabricated by the mechanochemical method. And the crucial factor which affects on battery performance was also examined.

• Journal of the Korean Electrochemical Society
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• v.6 no.4
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• pp.266-270
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• 2003

The $LiN_{0.8}Co_{0.2}O_2$ has shown outstanding electrochemical properties. The microstructure of $LiN_{0.8}Co_{0.2}O_2$ cathode was investigated by using TEM (transmission electron microscopy) and X-ray diffraction techniques. The $LiN_{0.8}Co_{0.2}O_2$ was produced by sol-gel method to synthesize fine particles less than $1{\mu}m$ in the average diameter. In this study, emphasis was given to the examination and interpretation of the microstructural change during charge-discharge cycling experiments, which appeared to be one of the main causes of early degradation of rechargeable batteries. Results showed that the $1{\mu}m$ cathode produced by sol-gel method had high reversible capacity and excellent cycling stability due to its homogeneous distribution of Ni and Co cations on u atomic scale. In particular, the $1{\mu}m$ cathode did not show severe strain induced structural defects or cubic spinel disordering during cycling experiments, which had been observed in the conventional $LiCoO_2$ cathode. The $LiNi_{0.8}Co_{0.2-x}M_x[M=Al]$ compounds show good reversibility but low discharge capacity.

• Journal of the Korean Electrochemical Society
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• v.9 no.1
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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.

• Journal of Surface Science and Engineering
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• v.39 no.6
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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.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.37 no.3
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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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• v.20 no.5
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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.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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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.