• Bulletin of the Korean Chemical Society
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• v.34 no.1
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• pp.89-94
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• 2013

Layered $Li_{1+x}(Mn_{0.4}Ni_{0.4}Fe_{0.2})_{1-x}O_2$ (0 < x < 0.3) solid solutions were synthesized using solgel method with adipic acid as chelating agent. Structural and electrochemical properties of the prepared powders were examined by means of X-ray diffraction, Scanning electron microscopy and galvanostatic charge/discharge cycling. All powders had a phase-pure layered structure with $R\bar{3}m$ space group. The morphological studies confirmed that the size of the particles increased at higher x content. The charge-discharge profiles of the solid solution against lithium using 1 M $LiPF_6$ in EC/DMC as electrolyte revealed that the discharge capacity increases with increasing lithium content at the 3a sites. Among the cells, $Li_{1.2}(Mn_{0.32}Ni_{0.32}Fe_{0.16})O_2$ (x = 0.2)/$Li^+$ exhibits a good electrochemical property with maximum initial capacity of 160 $mAhg^{-1}$ between 2-4.5 V at 0.1 $mAcm^{-2}$ current density and the capacity retention after 25 cycles was 92%. Whereas, the cell fabricated with x = 0.3 sample showed continuous capacity fading due to the formation of spinel like structure during the subsequent cycling. The preparation of solid solutions based on $LiNiO_2-LiFeO_2-Li_2MnO_3$ has improved the properties of its end members.

• Journal of the Korean Electrochemical Society
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• v.7 no.1
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• pp.21-25
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• 2004

The electrochemical behaviors of dissolved hydrogen and hydrogen peroxide at a platinum disk electrode were investigated in boric acid solution by potentiostatic polarization method at the temperature of 25 and $200^{\circ}C$. The oxidation of dissolved hydrogen at $25^{\circ}C$ was kinetically controlled reaction, the rate of which depends upon the electron transfer on the electrode surface. As temperature was raised, however, the electrochemical characteristics of dissolved hydrogen were changed from a kinetically controlled reaction to a diffusion controlled one. One notable feature, with dissolved hydrogen at high temperature, is that an abnormal potential range was observed, where the oxidation rate of dissolved hydrogen rapidly decreased just before starting potential of water oxidation. We think it is caused by the deactivation of the electrode that results from the adsorption of hydroxyl ion on the surface of the platinum disk. On the contrary, a definite change with temperature was not identified in the case of the hydrogen peroxide except for the increase in current density that was due to the increasing diffusion coefcient with an increase of temperature.

• Korean Chemical Engineering Research
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• v.57 no.6
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• pp.861-867
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• 2019

$Li_4Ti_5O_{12}$ is a promising next-generation anode material for lithium-ion batteries due to excellent cycle life, low irreversible capacity, and little volume expansion during charge-discharge process. However, it has poor charge capacity at high current density due to its low electrical conductivity. To improve this weakness, porous $Li_4Ti_5O_{12}$ was synthesized by sol-gel method with P123 as chelating agent. The physical characteristics of as-prepared sample was investigated by XRD, SEM, and BET analysis, and electrochemical properties were characterized by cycle performance test, cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS). $Li_4Ti_5O_{12}$ synthesized by 0.01mol ratio of P123/Ti showed most unified particle size, high specific surface area, and relatively high porosity. EIS analysis showed that depressed semicircle size was remarkably reduced, which suggested resistance value in electrode was decreased. Capacity in rate performance showed 178 mAh/g at 0.2C, 170 mAh/g at 0.5C, 110 mA/h at 5C, and 90 mAh/g at 10C. Capacity retention also showed 99% after rate performance.

• Membrane Journal
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• v.29 no.3
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• pp.173-182
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• 2019

Much research has been made for finding new and eco-friendly alternative sources of energy to solve the problems related with the pollution caused by emissions of greenhouse gases such as carbon dioxide as the use of fossil fuels increases worldwide. Among them, fuel cells draws particular interests as an eco-friendly energy generator because only water is obtained as a by-product. Anion exchange membrane-based alkaline fuel cell (AEMFC) that uses anion exchange membrane as an electrolyte is of increased interest recently because of its advantages in using low-cost metal catalyst unlike the PEMFC (potton exchange membrane fuel cell) due to the high-catalyst activity in alkaline conditions. The main properties required as an anion exchange membrane are high hydroxide conductivity and chemical stability at high pH. Recently we reported a chemically crosslinked poly(2-dimethyl-1,4-phenylene oxide) (PPO) by reacting PPO with N,N,N',N'-tetramethyl-1,6-hexanediamine as novel anion exchange membranes. In the current work, we further developed the same crosslinked polymer but having enhanced physicochemical properties, including higher conductivity, increased mechanical and dimensional stabilities by using the PPO with a higher molecular weight and also by increasing the crosslinking density. The obtained polymer membrane also showed a good cell performance.

• Korean Chemical Engineering Research
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• v.60 no.4
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• pp.574-581
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• 2022

Nanofibers comprising reduced graphene oxide (rGO) and Mo₂C/Mo₂N nanoparticles (Mo₂C/Mo₂N rGO NFs) were prepared for a functional interlayer of Li-S batteries (LSBs). The well-dispersed Mo₂C and Mo₂N nanoparticles in the nanofiber structure served as active polar sites for efficient immobilization of dissolved lithium polysulfide. The rGO nanosheets in the structure also provide conductive channels for fast ion/electron transport during charging-discharging and ensured reuse of lithium polysulfide during redox reactions through a fast charge transfer process. As a result, the cell assembled with Mo₂C/Mo₂N rGO NFs-coated separator and pure sulfur electrode (70 wt% of sulfur content and 2.1 mg cm^-2 of sulfur loading) showed a stable discharge capacity of 476 mA h g^-1 after 400 charge-discharge cycles at 0.1 C. Furthermore, it exhibited a discharge capacity of 574 mA h g^-1 even at a high current density of 1.0 C. Therefore, we believe that the proposed unique nanostructure synthesis strategy could provide new insights into the development of sustainable and highly conductive polar materials as functional interlayers for high performance LSBs.

• Journal of the Korean Electrochemical Society
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• v.25 no.1
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• pp.1-12
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• 2022

Lithium metal is the most promising anode for next-generation lithium-ion batteries due to its lowest reduction potential (-3.04 V vs. SHE) and high specific capacity (3860 mAh/g). However, the dendritic formation under high charging current density remains one of main technical barriers to be used for commercial rechargeable batteries. To address these issues, tremendous research to suppress lithium dendrite formation have been conducted through new electrolyte formulation, robust protection layer, shape-controlled lithium metal, separator modification, etc. However, Li/Li symmetric cell test is always a starting or essential step to demonstrate better lithium dendrite formation behavior with lower overpotential and longer cycle life without careful analysis. Thus, this review summarizes overpotential behaviors of Li/Li symmetric cells along with theoretical explanations like initial peaking or later arcing. Also, we categorize various overpotential data depending on research approaches and discuss them based on peaking and arcing behaviors. Thus, this review will be very helpful for researchers in lithium metal to analyze their overpotential behaviors.

• Journal of the Korean Electrochemical Society
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• v.2 no.3
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• pp.123-129
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• 1999

Initial electrochemical characteristics of $LiCoO_2$ electrode for lithium ion battery with various content of super s black as conductive material were evaluated through the charge/discharge with the potential range of 4.3V to 2.0V versus $Li^+/Li^+$. The rate of C/4 and C/2 by the 3 electrode test cell composed with an electrolytic solution of 1 mol/l $LiPF_6/EC+DEC(1:3\;by\; weight)$. Lithium was used as reference electrode. High impedance charge behavior was observed at early stage of charge. In the case of $3\%w/w$ of super s black as conductive material, the specific resistance of the high impedance releasing was $3.82\;{\Omega}\;{\cdot}\;g-LiCoCo_2$ at the current density of $0.5 mA/cm^2$, which corresponds 7 times of the specific resistance of electrode $(0.728 g-LiCoO_2)$. At second charge, the specific resistance of the high impedance releasing was 63 mn · g-Lico02, which corresponds 12eio of the specific resistance of electrode and only $1.7\%$ of that of the first charge. The first charge and discharge specific capacities at C/4 rate were 160-161 and $153\~155mAh/g-LiCoO_2$, respectively, to lead $95.4\~96.4\%$ of coulombic efficiencies and ca. $6 mAh/g-LiCoO_2$ of initial irreversible specific capacity. Specific resistance at the end of charge and rest showed low value at content of super s black between 2 and $7\%w/w$, which agreed with characteristics of irreversible specific capacity. Capacity densities were reduced by the increasing the content of conductive material. They were 447 and 431mAh/ml when 2 and $2.9\%w/w$ of super s black were used, respectively, at the rate of C/4.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.100-101
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• 2012

The plasma damage free and room temperature processedthin film deposition technology is essential for realization of various next generation organic microelectronic devices such as flexible AMOLED display, flexible OLED lighting, and organic photovoltaic cells because characteristics of fragile organic materials in the plasma process and low glass transition temperatures (Tg) of polymer substrate. In case of directly deposition of metal oxide thin films (including transparent conductive oxide (TCO) and amorphous oxide semiconductor (AOS)) on the organic layers, plasma damages against to the organic materials is fatal. This damage is believed to be originated mainly from high energy energetic particles during the sputtering process such as negative oxygen ions, reflected neutrals by reflection of plasma background gas at the target surface, sputtered atoms, bulk plasma ions, and secondary electrons. To solve this problem, we developed the NBAS (Neutral Beam Assisted Sputtering) process as a plasma damage free and room temperature processed sputtering technology. As a result, electro-optical properties of NBAS processed ITO thin film showed resistivity of $4.0{\times}10^{-4}{\Omega}{\cdot}m$ and high transmittance (>90% at 550 nm) with nano- crystalline structure at room temperature process. Furthermore, in the experiment result of directly deposition of TCO top anode on the inverted structure OLED cell, it is verified that NBAS TCO deposition process does not damages to the underlying organic layers. In case of deposition of transparent conductive oxide (TCO) thin film on the plastic polymer substrate, the room temperature processed sputtering coating of high quality TCO thin film is required. During the sputtering process with higher density plasma, the energetic particles contribute self supplying of activation & crystallization energy without any additional heating and post-annealing and forminga high quality TCO thin film. However, negative oxygen ions which generated from sputteringtarget surface by electron attachment are accelerated to high energy by induced cathode self-bias. Thus the high energy negative oxygen ions can lead to critical physical bombardment damages to forming oxide thin film and this effect does not recover in room temperature process without post thermal annealing. To salve the inherent limitation of plasma sputtering, we have been developed the Magnetic Field Shielded Sputtering (MFSS) process as the high quality oxide thin film deposition process at room temperature. The MFSS process is effectively eliminate or suppress the negative oxygen ions bombardment damage by the plasma limiter which composed permanent magnet array. As a result, electro-optical properties of MFSS processed ITO thin film (resistivity $3.9{\times}10^{-4}{\Omega}{\cdot}cm$, transmittance 95% at 550 nm) have approachedthose of a high temperature DC magnetron sputtering (DMS) ITO thin film were. Also, AOS (a-IGZO) TFTs fabricated by MFSS process without higher temperature post annealing showed very comparable electrical performance with those by DMS process with $400^{\circ}C$ post annealing. They are important to note that the bombardment of a negative oxygen ion which is accelerated by dc self-bias during rf sputtering could degrade the electrical performance of ITO electrodes and a-IGZO TFTs. Finally, we found that reduction of damage from the high energy negative oxygen ions bombardment drives improvement of crystalline structure in the ITO thin film and suppression of the sub-gab states in a-IGZO semiconductor thin film. For realization of organic flexible electronic devices based on plastic substrates, gas barrier coatings are required to prevent the permeation of water and oxygen because organic materials are highly susceptible to water and oxygen. In particular, high efficiency flexible AMOLEDs needs an extremely low water vapor transition rate (WVTR) of $1{\times}10^{-6}gm^{-2}day^{-1}$. The key factor in high quality inorganic gas barrier formation for achieving the very low WVTR required (under ${\sim}10^{-6}gm^{-2}day^{-1}$) is the suppression of nano-sized defect sites and gas diffusion pathways among the grain boundaries. For formation of high quality single inorganic gas barrier layer, we developed high density nano-structured Al2O3 single gas barrier layer usinga NBAS process. The NBAS process can continuously change crystalline structures from an amorphous phase to a nano- crystalline phase with various grain sizes in a single inorganic thin film. As a result, the water vapor transmission rates (WVTR) of the NBAS processed $Al_2O_3$ gas barrier film have improved order of magnitude compared with that of conventional $Al_2O_3$ layers made by the RF magnetron sputteringprocess under the same sputtering conditions; the WVTR of the NBAS processed $Al_2O_3$ gas barrier film was about $5{\times}10^{-6}g/m^2/day$ by just single layer.