• Korean Chemical Engineering Research
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• v.55 no.3
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• pp.307-312
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• 2017

In this study, the electrochemical performance of surface modified carbon using the PFO (pyrolyzed fuel oil) was investigated by chemical activation with KOH and $K_2CO_3$. PFO was heat treated at $390{\sim}400^{\circ}C$ for 1~3h to prepared the pitch. Three carbon precursors (pitch) prepared by the thermal reaction were 3903 (at $390^{\circ}C$ for 3h), 4001(at $400^{\circ}C$ for 1h) and 4002 (at $400^{\circ}C$ for 2h). Also, the effect of chemical activation catalysts and mixing time on the development of porosity during carbonization was investigated. The prepared carbon was analyzed by BET and FE-SEM. It was shown that chemical activation with KOH could be successfully used to develop carbon with specific surface area ($3.12m^2/g$) and mean pore size (22 nm). The electrochemical characteristics of modified carbon as the anode were investigated by constant current charge/discharge, cyclic voltammetry and electrochemical impedance tests. The coin cell using pitch (4002) modified by KOH has better initial capacity (318 mAh/g) than that of other pitch coin cells. Also, this prepared carbon anode appeared a high initial efficiency of 80% and the retention rate capability of 2C/0.1 C was 92%. It is found that modified carbon anode showed improved cycling and rate capacity performance.

• Journal of the Korean Electrochemical Society
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• v.2 no.2
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• pp.81-87
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• 1999

Poly-acrylonitrile (PAN) based carbon fibers were stabilized under various tensions in the presence of air at about $200^{\circ}C$ and sequentially carbonized under some different gas environments in the range of 700 to $1500^{\circ}C$. The prepared carbon fibers were used for rechargeable lithium ion battery anode to investigate preparation parameters effects on electrochemical characteristics. It was found that the tension during stabilization, carbonization temperature and gas atmospheres affect the carbon fiber properties such as conductivity, mechanical strength, surface morphology and diffusion coefficient of lithium ion, which are closely related to the on electrolchemical properties as well as the charge/discharge characteristics.

• Journal of the Korean Electrochemical Society
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• v.19 no.3
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• pp.101-106
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• 2016

In this study, we prepared an ionic liquid composite solid polymer electrolyte (PEO-LiTFSI-$Pyr_{14}TFSI$) with poly(ethylen oxide), lithium bis(trifluoromethanesulfonyl)imide, N-butyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide by blending-cross linking process. Although the PEO-LiTFSI-$Pyr_{14}TFSI$ composite solid polymer electrolyte displayed a small peak at 4.4 V, it had high electrochemical oxidation stability up to 5.7 V. Ionic conductivity of the PEO-LiTFSI-$Pyr_{14}TFSI$ composite solid polymer electrolyte increased with increasing temperature from $10^{-6}S\;cm^{-1}$ at $30^{\circ}C$ to $10^{-4}S\;cm^{-1}$ at $70^{\circ}C$. To investigate the electrochemical properties, the PEO-LiTFSI-$Pyr_{14}TFSI$ composite solid polymer electrolyte assembled with $LiFePO_4$ cathode and Li-metal anode. At 0.1 C-rate, the cell delivered $40mAh\;g^{-1}$ for $30^{\circ}C$, $69.8mAh\;g^{-1}$ for $40^{\circ}C$ and $113mAh\;g^{-1}$ for $50^{\circ}C$, respectively. The PEO-LiTFSI-$Pyr_{14}TFSI$ solid polymer electrolyte exhibited good charge-discharge performance in Li/SPE/$LiFePO_4$ cells at $50^{\circ}C$.

• Journal of the Korean Electrochemical Society
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• v.11 no.4
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• pp.284-288
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• 2008

Sn-thin film as high capacitive anode for thin film lithium-ion battery was prepared by organic-electrolyte electroplating using Sn(II) acetate. Electrolytic solution including $Li^+$ and $Sn^{2+}$ had 3 reduction peaks at cyclic voltammogram. Current peak at $2.0{\sim}2.5\;V$ region correspond to the electroplating of Sn on Ni substrate. This potential value is lower than 2.91 V vs. $Li^+/Li^{\circ}$, of the standard reduction potential of $Sn^{2+}$ under aqueous media. It is the result of high overpotential caused by high resistive organic electrolytic solution and low $Sn^{2+}$ concentration. Physical and electrochemical properties were evaluated using by XRD, FE-SEM, cyclic voltammogram and galvanostatic charge-discharge test. Crystallinity of electroplated Sn-anode on a Ni substrate could be increased through heat treatment at $150^{\circ}C$ for 2 h. Cyclic voltammogram shows reversible electrochemical reaction of reduction(alloying) and oxidation(de-alloying) at 0.25 V and 0.75 V, respectively. Thickness of Sn-thin film, which was calculated based on electrochemical capacity, was $7.35{\mu}m$. And reversible capacity of this cell was $400{\mu}Ah/cm^2$.

• Clean Technology
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• v.23 no.3
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• pp.308-313
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• 2017

In this study, we investigated the electrocatalytic effects of the N and O co-doping of Graphite Felt (GF) electrode for the vanadium redox flow battery (VRFB) at the cathode and the anode reaction, respectively. The electrodes were prepared by chemical vapor deposition (CVD) with $NH_3-O_2$ at 773 K, and its effects were compared with an electrode prepared by an O doping treatment. The surface morphology and chemical composition of the electrodes were characterized by scanning electron microscopy (SEM) and photoelectron spectroscopy (XPS). The electrocatalytic properties of these electrodes were characterized in a VRFB single cell comparing the efficiencies and performance of the electrodes at the cathode, anode, and single cell level. The results exhibited about 2% higher voltage and energy efficiencies on the N-O-GF than the O-GF electrode. It was found that the N and O co-doping was particularly effective in the enhancement of the reduction-oxidation reaction at the anode.

• The Korean Journal of Ecology
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• v.22 no.5
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• pp.235-240
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• 1999

Characterization of water quality was performed from March 1993 to March 1998, on the purpose of clarifying the relationships between water quality and land use types. The study sites were two reservoir basins; Kaesim and Jangchan in Iwon-myon, Okchon-gun, Chungcho'ngbukdo Province. The two basins were characterized by cultivated area (Kaesim reservoir) and mountain area (Jangchan reservoir), and divided into eleven small basins, where dynamics of pollutants, and the relationship between water quality and land use types were investigated. BOD, SS and TKN became lower and lower from up-stream to down-stream, except for the small basin G where self-purification limit was exceeded. And water quality of Jangchan reservoir basin was worse because of fish nursery. Area below altitude 200m occupied 56% in Kaesim and 44% in Jangchan reservoir basins. Especially total phosphorous (Y/sub T-P/=0.2023X＋0.0991, r=0.54) and total nitrogen increased in small basins where the proportion of cultivated and residential area was higher. The analysis of influences of pollutant discharge on water quality showed that pollution charge was very high in cultivated areas. The concentrations of pollutants were attenuated flowing into watersheds through physical, chemical, biochemical, and biological processes. The pollution level of mountain area was lower than that of cultivated areas.

• Journal of the Korean Electrochemical Society
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• v.4 no.3
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• pp.104-108
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• 2001

Naphthalene derived mesophase pitch WP) was spun into short fibers by using melt-blown technology. The pitch fibers oxidative stabilization were carried out heating rates of $2^{\circ}C/min,\;5^{\circ}C/min\;and\; 10^{\circ}/min$. The heating rate was a key factor to maximate the capacity of the Li-ion secondary battery through controlling the morphology of the graphitized fiber. The diameters of the melt-blown fibers prepared were in the range of $4{\mu}m\~16{\mu}m$ with functions of air jet speed, air temperature and the temperature of the nozzle. The graphitized fibers of $10{\mu}m$ diameters showed various morphological structure with heating rate of the stabilization. Radial, radial-random and skin-core cross-sectional structure of the fibers were observed at the respective heating rate of $2^{\circ}C/min\;5^{\circ}C/min\;and\;10^{\circ}C/min$. Most crystalline structure of graphite was obtained from the fiber stabilized at heating rate of $10^{\circ}C/min$ exhibiting the best anode performance with 400 mAh/g of capacitance and $96.8\%$ of charge/discharge efficiency.

• Journal of the Korean Electrochemical Society
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• v.14 no.3
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• pp.184-190
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• 2011

$LiMn_2O_4$ with mesoporous hollow sphere shape was synthesized by precipitation method with silica template. The synthesized $LiMn_2O_4$ has nanosized first particle and mesoporous hollow sphere shape. Silica template was removed by chemical etching method using NaOH solution. When the concentration of NaOH solution was increased, first particle size of manganese oxide was decrease and confirmed mesoporous hollow shpere shape. X-ray diffraction(XRD) patterns revealed that the synthesized samples has spinel structure with Fd3m space group. In case the ratio of silica and maganese salt increased, the size of first particles was decreased. The tetragoanal $LiMn_2O_4$ with micron size was synthesized at ratio of silica and manganese salt over 1 : 9. The prepared samples were assembled as cathode materials of Li-ion battery with 2032 type coin cell and their electrochemical properties are examined by charge-discharge and cyclic performance. Electrochemical measurements show that the nano-size particles had lower capacity than micron-size particles. But, cyclic performance of nano-size particles had better than that of micron-size particles.

• Applied Chemistry for Engineering
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• v.21 no.5
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• pp.590-592
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• 2010

Li-Mn spinel ($LiMn_2O_4$) is prepared by a hydrothermal process with K-Birnessite ($KMnO_4{\cdot}yH_2O$) as a precursor. The K-Birnessite obtained via a hydrothermal process with potassium permanganate [$KMnO_4$] and urea [$CO(NH_2)_2$] as starting materials are converted to Li-Mn spinel nanoparticles reacting with LiOH. The molar ratio of LiOH/K-Birnessite is adjusted in order to find the effect of the ratio on the structural, morphological and electrochemical performances of the Li-Mn spinel. X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDS), and thermogravimetry (TG) are used to investigate the crystal structure and morphology of the samples. Galvanostatic charge and discharge are carried out to measure the capacity and rate capability of the Li-Mn spinel. The capacity shows a maximum value of $117\;mAhg^{-1}$ when the molar ratio of LiOH/K-Birnessite is 0.8 and decreases with the increase of the ratio. However the rate capability is improved with the increase of the ratio due to the reduction of the particle size.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.3 no.4
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• pp.269-278
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• 2005

In order to produce only a pH-controlled solution without discharging any unwanted solution, this work has developed a continuous electrolytic system with a pH-adjustment reservoir being placed before an ion exchange membrane-equipped electrolyzer, where as a target solution was fed into the pH-adjustment reservoir, some portion of the solution in the pH-adjustment reservoir was circulated through the cathodic or anodic chamber of the electrolyzer depending on the type of the ion exchange membrane used, and some other portion of the solution in the pH-adjustment reservoir was discharged from the electrolytic system through the other counter chamber with its pH being controlled. The internal circulation of the pH-adjustment reservoir solution through the anodic chamber in the case of using a cation exchange membrane and that through the cathodic chamber in the case of using an anion exchange membrane could make the solution discharged from the other counter chamber effectively acidic and basic, respectively. The phenomena of the pH being controlled in the system could be explained by the electro-migration of the ion species in the solution through the ion exchange membrane under a cell potential difference between anode and cathode and its consequently-occurring non-charge equilibriums and electrolytic water- split reactions in the anodic and cathodic chambers.