• Journal of the Korean Electrochemical Society
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• v.4 no.3
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• pp.113-117
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• 2001

Specific capacitance and charge-discharge rate of EDLC using activated carbon electrode were affected by the compositions of electrolytes, the conditions of charge-discharge and physical properties of activated carbon materials. The activated carbon electrode was prepared by dip coating method. Charge-discharge test and electrochemical experiments were carried out for various kinds of organic electrolytes. Effects of charge and discharge current density on the specific capacitance were studied. Characteristics of leakage current, self-discharge and time-voltage curves in optimum conditions of organic electrolytes were compared with conventional $1M-Et_4NBF_4/PC$ electrolyte. The EDLC using MSP-20(specific surface area: $2000m^2/g$) electrode and $1M-LiPF_6/PC-DEC(1:1)$ was exhibited th highest specific capacitance of 130F/g and low polarization resistances. The EDLC using MSP-20 electrode at $1M-LiPF_6/PC-DEC(1:1)$ was small leak current of 0.0004A for 15min, long voltage retention of 0.8V after 100h and linear time-voltage curves with small IR-drop.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.18 no.5
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• pp.1155-1161
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• 2014

This paper proposes a start-up voltage generator for reducing the minimum input supply voltage of DC-DC boost converters to 250mV. The proposed start-up voltage generator boosts 250mV input voltage to over 500mV to charge the capacitor for starting the boost converter. After the boost converter operates initially with the supply voltage charged in the capacitor, it uses its boosted output voltage for the supply voltage. Therefore, after the start-up operation, the proposed DC-DC boost converter works as the same as the conventional one. The proposed start-up voltage generator reduces the threshold voltage of the transistors by adjusting the body voltage at a low input voltage. This causes the higher clock frequency and the larger current to a Dickson charge-pump for boosting the input voltage. The proposed start-up voltage generator was implemented with a $0.18{\mu}m$ CMOS process. Its clock frequency and output voltage were 34.5kHz and 522mV at 250mV input voltage, respectively.

• Applied Chemistry for Engineering
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• v.27 no.4
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• pp.415-420
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• 2016

To enhance electrochemical performances of anode materials, the surface of coal tar pitch (CTP) was modified by incorporating heteroatoms through chemical treatment with phosphoric acid ($H_3PO_4$). The prepared anode materials with modified CTP was analyzed by XRD, FE-SEM and XPS. The electrochemical performances of modified CTP were investigated by constant current charge/discharge test, rate performance, cyclic voltammetry and impedance tests using the electrolyte of $LiPF_6$ dissolved in the mixed organic solvents (ethylene carbonate : dimethyl carbonate = 1 : 1 vol% + vinylene carbonate 3 wt%). The coin cell using modified CTP ($H_3PO_4/CTP$ = 3 : 100 in weight) has better initial capacity and initial efficiency (489 mAh/g, 82%) than those of other composition coin cells. Also, it was found that the capacity retention was 86% after 30 cycles and the rate capability was 87% at 2 C/0.1 C.

• Applied Chemistry for Engineering
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• v.27 no.4
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• pp.439-443
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• 2016

In this report, $MnO_2$ nanoparticle-deposited functionalized graphene sheets were prepared and their superior electrochemical performances were demonstrated by cyclic voltammetry, galvanostatic charge-discharge, and impedance analysis. Ionic liquids were employed to functionalize the surface of reduced graphene oxides (RGOs), leading to prevention of the aggregation of RGO sheets and abundant growth sites for deposition of $MnO_2$ nanoparticles. As-prepared $MnO_2/RGO$ nanocomposites were characterized using scanning electron microscope, transition electron microscope, X-ray photoelectron spectroscopy, and X-ray diffraction. Electrochemical properties of $MnO_2/RGO$ electrode were evaluated using $Na_2SO_4$ electrolyte under a three-electrode system. The $MnO_2/RGO$ electrode showed a high specific capacitance (251 F/g), a high rate capability (80.5% retention), and long-term stability (93.6% retention).

• Journal of the Korean Electrochemical Society
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• v.14 no.2
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• pp.77-82
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• 2011

The surface of $Li[Ni_{0.35}Co_{0.3}Mn_{0.35}]O_2$ cathode was modified by $[Li,La]TiO_3$ coating using pH controlled coating solution. At low pH values (acidic solution), cathode powders, which is oxides, have a positive surface charge, whereas, they have a negative surface charge at high pH values. As a result, their charge could affect the formation of the coating layer on the surface of cathode powder. To determine the optimal pH value, the surface coating of the pristine powder was carried out at various pH values of the coating solution. The surface morphology of coated samples was characterization by SEM and TEM analyses. Impedance analysis and cyclic voltammogram presented that internal resistance of the cell was dependent upon the pH of coating solution.

• Transactions of the Korean hydrogen and new energy society
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• v.28 no.1
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• pp.56-62
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• 2017

Although most electricity production contributes to air pollution, the vehicle organizations and environmental agency categorizes all EVs as zero-emission vehicles because they produce no direct exhaust or emissions. Currently available EVs have a shorter range per charge than most conventional vehicles have per tank of gas. EVs manufacturers typically target a range of 160 km over on a fully charged battery. The energy efficiency and driving range of EVs varies substantially based on driving conditions and driving habits. Extreme outside temperatures tend to reduce range, because more energy must be used to heat or cool the cabin. High driving speeds reduce range because of the energy required to overcome increased drag. Compared with gradual acceleration, rapid acceleration reduces range. Additional devices significant inclines also reduces range. Based on these driving modes and climate conditions, this paper discusses the performance characteristics of EVs on energy efficiency and driving range. Test vehicles were divided by low / high-speed EVs. The difference of test vehicles are on the vehicle speed and size. Low-speed EVs is a denomination for battery EVs that are legally limited to roads with posted speed limits as high as 72 km/h depending on the particular laws, usually are built to have a top speed of 60 km/h, and have a maximum loaded weight of 1,400 kg. Each vehicle test was performed according to the driving modes and test temperature ($-25^{\circ}C{\sim}35^{\circ}C$). It has a great influence on fuel efficiency amd driving distance according to test temperature conditions.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.42 no.2
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• pp.150-157
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• 2014

Li-Ion battery is used in the most satellites now due to advantages such as weight, thermal dissipation and self discharge compared to the previous generations of electrochemical batteries. The performance analysis model of the Li-Ion battery is needed to aid the design of new satellite electrical power subsystem. This paper develops the performance analysis model of the Li-Ion battery to apply to the electrical power subsystem design and energy balance analysis on geostationary orbit. The analysis model receives the satellite bus power, solar array power and battery temperature and gives the battery voltage, charge and discharge currents, taper index, state of charge and power dissipation. The results from the performance analysis are compared and analyzed with the flight data to verify the model. The compared results show satisfactory without significant difference with the flight data.

• Journal of the Korean Electrochemical Society
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• v.15 no.3
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• pp.115-123
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• 2012

As the market of lithium secondary batteries moves from mobile IT devices to large-format electric vehicles or energy storage systems, the strengthened battery specifications such as long-term reliability longer than 10 years, pack-level safety and tough competitive price have been required. Moreover, even though high power properties should also be achieved for hybrid electric vehicles, it is not easy to measure accurate power values at various conditions. Because it is difficult to choose a proper measurement method and its experimental condition is more complex comparing to capacity measurement. In addition, the power values are very sensitive to power duration time, state-of-charge (SOC) of cells, cut-off voltages, and temperatures, whereas capacity values are not. In this paper, we introduce three kinds of power measurement methods, hybrid pulse power characterization (HPPC) suggested by US FreedomCar, so-called J-pulse by Japan electric vehicle association standards (JEVS) and constant power measurement, respectively. Moreover, with pouch-type unit cells for HEV, experimental power data are discussed in order to compare each power measurement.

• Journal of the Korean Chemical Society
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• v.46 no.6
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• pp.528-534
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• 2002

We have studied to find the optimum electrolyte that satisfied high ionic conductivity, large elec-trochemical window, etc in Li-ion battery. And also studied were the effect of a passive film on carbon anode surface,which is formed by solvent decomposition during the initial charge process. Electrochemical properties of the passive film formed on carbon anode surface investigated and explained as the volumetric ratio of the mixed solvents. The results of scanning electron microscopy, chronopotentiometry, cyclic voltammetry, impedance spectroscopy revealed that the electrochemical properties of the passive film were varied with the ionic conductivity of the electrolyte including the mixed solvents.

• Journal of the Institute of Electronics Engineers of Korea SC
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• v.41 no.6
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• pp.17-25
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• 2004

In this paper, we propose a new small swing domino logic for low-power consumption. To reduce the power consumption, both the precharge node and the output node swing the range from 0 to $V_{REF}$- $V_{THN}$, where $V_{REF}$=VDD-n $V_{THN}$ (n=1, 2, and 3). This can be done by adding the inverter structure on domino logic that allows a full swing or a small swing on its input terminal without leakage current. Compared to previous works, the proposed structure can save the power consumption of more than 30% for n=0, 1, 2, and 3 in the equation of $V_{REF}$=VDD-n $V_{THN}$. A multiplier applying the proposed domino logic has been designed and fabricated using a 0.35-${\mu}{\textrm}{m}$ n-well CMOS process under 3.3-V supply voltage. Compared with other previous works, it shows a 30% power reduction and a better feature in power-delay product.lay product.