• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2005.11a
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• pp.350-351
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• 2005

The electrochemical behavior of Si-C material synthesized by heating the mixture of silicon and polyvinylidene fluoride (PVDF). Coin cells of the type 2025 were made using the synthesized material and the electrochemical studies were performed. Si-C/Li cells were made by using the developed Si-C material. Charge/discharge test was performed at 0.1C hour rate. Initial charge and discharge capacities at Si-C material derived from 20 wt.% of PVDF was found to be 1,830 and 526 mAh/g respectively. Initial charge/discharge characteristics of the electrode were analyzed. The level of reversible specific capacity was about 216 mAh/g at Si-C material derived from 20 wt.% of PVDF, IIE, intercalation efficiency at initial charge/discharge, was 68 %. Surface irreversible specific capacity was 31 mAh/g, and average specific resistance was 2.6 ohm*g.

• Journal of the Korean institute of surface engineering
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• v.52 no.2
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• pp.96-102
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• 2019

Magnesium and its alloys are prone to be corroded, thus surface treatments improving corrosion resistance are always required for practical applications. As a surface treatment of magnesium alloys, plasma electrolytic oxidation (PEO), creating porous stable oxide layer by a high voltage discharge in electrolyte, enhances the corrosion resistance. However, due to superhydrophilicity of the porous oxide layer, which easily allow the penetration of corrosive media toward magnesium alloys substrate, post-treatments inhibiting the transfer of corrosive media in porous oxide layer are required. In this work, we employed a hydrophobizing method to enhance the corrosion resistance of PEO treated Mg alloy. Three types of hydrophobizing techniques were used for PEO layer. Thin Teflon coating with solvent evaporation, self-assembled monolayer (SAM) coating of octadecyltrichlorosilane (OTS) based on solution method and SAM coating of perfluorodecyltrichlorosilane (FDTS) based on vacuum method significantly enhances corrosion resistance of PEO treated Mg alloy with reducing the contact of water on the surface. In particular, the vacuum based FDTS coating on PEO layer shows the most effective hydrophobicity with the highest corrosion resistance.

• KEPCO Journal on Electric Power and Energy
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• v.2 no.4
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• pp.601-608
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• 2016

The electrical characteristics of the soil where a ground electrode is buried vary with regions, seasons and environmental factors. Electrical discharge in the vicinity of the ground electrode will occur differently and significantly affect the performance of the grounding system. It is necessary to analyze discharge and ionization characteristics of soils when the grounding system is designed. The aims of this investigation are to understand correlation between the soil ionization and the transient ground impedance. This paper presents the experimental results on the soil ionization parameters and the transient ground resistance due to the soil ionization around a hemispherical ground electrode stressed by lightning impulse voltages.

• The Transactions of the Korean Institute of Power Electronics
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• v.23 no.3
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• pp.174-181
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• 2018

This study introduces a systematic approach to selecting the internal parameters applied to the equivalent electrical-circuit model (EECM) of a lithium titanium oxide ($Li_4Ti_5O_{12}$; LTO) rechargeable cell. Based on the dynamic characteristic of the cell, a simplified EECM consisting of an open-circuit voltage (OCV), an ohmic resistance, and an RC ladder is fabricated. To select the internal parameters of a simplified EECM, experiments on discharge capacity, OCV, and discharge/charge resistances are performed using hybrid pulse power characterization and direct current internal resistance (DCIR) measurements over the full state-of-charge (SOC) range. The experimental results of the LTO rechargeable cell highlight the importance of correct selection of internal parameters that can reduce EECM errors. This study clearly provides experimental procedures, internal parameters results, and EECM guidelines for adaptive control-based SOC estimation for LTO rechargeable cells.

• 유체기계공업학회:학술대회논문집
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• 2000.12a
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• pp.259-264
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• 2000

The functions of the plug valve are the control of flow rate as well closing and opening pipe lines. Analyses on the flow characteristics in plug valve port are required to improve the performance and safety at severe operating conditions such as high-pressure and high-temperature. In this study, numerical analyses are carried out with varying the opening rate (fraction of the full open to close) of the valve and the shapes of valve Uk: straight, convex, concave and mixed shapes. The parameters influencing the flow characteristics in the valve are the discharge coefficient( $C_v$) and the resistance coefficient( K). Therefore, the distributions of static pressure, velocity vector and stream lines are investigated, and $C_v$ and K are calculated in each opening rate and shape. In case of full open, the static pressure passed through the valve port has almost been recovered. However, in case of other opening rates, the pressure does not permanently regained due to pressure drop leading to loss. This phenomenon in each shape of the valve shows the different behaviors. Calculation results show that the mixed shape has the best flow attribute.

• Journal of Electrochemical Science and Technology
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• v.5 no.3
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• pp.87-93
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• 2014

The fluorine-substituted $0.3Li_2MnO_3{\cdot}0.7Li[Mn_{0.60}Ni_{0.25}Co_{0.15}]O_{2-x}F_x$ cathode materials were synthesized by using the transition metal precursor, $LiOH{\cdot}H_2O$ and LiF. This was to facilitate the movement of lithium ions by forming more compact SEI layer and to reduce the dissolution of transition metals. The $0.3Li_2MnO_3{\cdot}0.7Li[Mn_{0.60}Ni_{0.25}Co_{0.15}]O_{2-x}F_x$ cathode material was sphere-shaped and each secondary particle had $10{\sim}15{\mu}m$ in size. The fluorine-substituted cathodes initially delivered low discharge capacity, but it gradually increased until 50th charge-discharge cycles. These results indicated that fluorine substitution gave positive effects on the structural stabilization and resistance reduction in materials.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1996.11a
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• pp.378-381
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• 1996

This study is to research Li$_{x}$Ni$_{2-x}$O$_2$ cathode for lithium chargeable battery. We investigated morphology and cell resistance, capacity and Ah efficiency of Li$_{x}$Ni$_{2-x}$O$_2$/Li cells using Li$_{x}$Ni$_{2-x}$O$_2$ prepared under air and $O_2$ flow. The (003)I/(104)I intensity ratio was 1.4. The cell resistance was increased with increasing Li in Li$_{x}$Ni$_{2-x}$O$_2$. The discharge capacity based on Li$_{x}$Ni$_{2-x}$O$_2$of 1st and 15th cycles was 135㎃h/g and 108㎃h/g, respectively. The Li$_{x}$Ni$_{2-x}$O$_2$ prepared with hexan under $O_2$ flow had a good properties. properties. properties.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.06a
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• pp.319-320
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• 2006

In order to improve the ESD(Electrical Static Discharge) resistance of multilayer chip varistors, we have investigated ZnO-$Pr_6O_{11}$ based chip varistor by applying tape casting technology, whose fundamental component were ZnO : $Pr_6O_{11}$ :$Co_3O_4$: $Y_2O_3$: $Al_2O_3$=93.67: 2.53:2.53:1.25 : 0.015 (wt %). The effect of sintering condition on the multilayer chip varistors and electric properties was studied. The electrical properties and ESD resistance of multilayer chip varistor could be influenced the sintering temperature and condition.

• Applied Chemistry for Engineering
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• v.30 no.1
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• pp.11-16
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• 2019

Ni-benzene-1,3,5-tricarboxylic acid based metal organic frameworks were successfully synthesized by hydrothermal method and thermally treated at various temperature. The electrochemical performance of composites was investigated using cyclic voltammetry, galvanostatic charge-discharge, and electrochemical impedance spectroscopy. Among all prepared composites, the samples annealed at $250^{\circ}C$ showed the highest capacitance with a low resistance, and high cycle stability. It was possible to obtain the low electrical resistance and high electric conductivity of the electrode by improved microstructure and morphology after the thermal annealing at $250^{\circ}C$. The samples annealed at $250^{\circ}C$ also displayed the maximum specific capacitance with a value of $953Fg^{-1}$ at a current density of $0.66A/g^{-1}$ in 6 M KOH electrolyte. Moreover, a 86.4% of the initial specific capacitance of the composite was maintained after 3,000 times charge-discharge cycle tests. Based on these properties, it can be concluded that the composite could be applied as potential supercapacitor electrode materials.

• Journal of the Korean Society of Safety
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• v.34 no.1
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• pp.21-26
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• 2019

This paper is purposed to develop hardware for controlling abnormal temperature that can occur environment and component itself in PCS. In order to be purpose, the hardware which is four part(sensing, PLC, monitoring and output) keep detecting temperature for critical components of PCS and can control the abnormal temperature. Apply to the hardware, it is selected to PV power generation facilities of 20 kW in Cheong-ju city and measured the data for one year in 2017. Through the temperature data, it is found critical components of four(discharge resistance, DC capacitor, IGBT, DSP board) and entered the setting value for operating the fan. The setting values for operating the fan are up to $130^{\circ}C$ in discharge resistance, $60^{\circ}C$ in DC capacitor, $55^{\circ}C$ in IGBT and DSP board. The hardware is installed at the same PCS(20 kW in Cheong-ju city) in 2018 and the power generation output is analyzed for the five days with the highest atmospheric temperature(Clear day) in July and August in 2017 and 2018 years. Therefore, the power generation output of the PV system with hardware increased up to 4 kWh.