• Bulletin of the Korean Chemical Society
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• v.32 no.3
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• pp.836-840
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• 2011

This study examines the effects of a carbon coating on the electrochemical performances of $LiFePO_4$. The results show that the capacity of bare $LiFePO_4$ decreased sharply, whereas the $LiFePO_4$/C shows a well maintained initial capacity. The Li ion diffusivity of the bare and carbon coated $LiFePO_4$ is calculated using cyclic voltammetry (CV) to determine the correlation between the electrochemical performance of $LiFePO_4$ and Li diffusion. The diffusion constants for $LiFePO_4$ and $LiFePO_4$/C measured from CV are $6.56{\times}10^{-16}$ and $2.48{\times}10^{-15}\;cm^2\;s^{-1}$, respectively, indicating considerable increases in diffusivity after modifications. The Li ion diffusivity (DLi) values as a function of the lithium content in the cathode are estimated by electrochemical impedance spectroscopy (EIS). The effects of the carbon coating as well as the mechanisms for the improved electrochemical performances after modification are discussed based on the diffusivity data.

• 한국전기화학회:학술대회논문집
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• 2004.04a
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• pp.77-77
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• 2004

• Journal of the Korean Electrochemical Society
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• v.5 no.4
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• pp.197-201
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• 2002

In this study, a gel polymer electrolyte was prepared from urethane acrylate and its electrochemical performances were evaluated. And, $LiCoO_2/GPE/graphite$ cells were prepared and their performances depending on discharge currents and temperatures were evaluated. The precursor containing $5 vol\%$ curable mixture had a low viscosity relatively. Ionic conductivity of the gel polymer electrolyte at room temperature and $-20^{\circ}C$ was ca. $5.9\times10^{-3}S{\cdot}cm^{-1}\;and\;1.7\times10^{-3}S{\cdot}cm^{-1}$, respectively. GPE showed electrochemical stability up to potential of 4.5V vs. $Li/Li^+.LiCoO_2/GPE/graphite$ cell showed a good high-rate and a low-temperature performance.

• Journal of the Korean Electrochemical Society
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• v.16 no.4
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• pp.204-210
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• 2013

Thin pore-filled cation and anion-exchange membranes (PFCEM and PFAEMs, $t_m=25-30{\mu}m$) were prepared using a porous polymeric substrate for efficient all-vanadium redox flow battery (VRB). The electrochemical and charge-discharge performances of the membranes have been systematically investigated and compared with those of commercially available ion-exchange membranes. The pore-filled membranes were shown to have higher permselectivity as well as lower electrical resistances than those of the commercial membranes. In addition, the VRBs employing the pore-filled membranes exhibited the respectable charge-discharge performances, showing the energy efficiencies (EE) of 82.4% and 84.9% for the PFCEM and PFAEM, respectively (cf. EE = 87.2% for Nafion 1135). The results demonstrated that the pore-filled ion-exchange membranes could be successfully used in VRBs as an efficient separator by replacing expensive Nafion membrane.

• Journal of Electrochemical Science and Technology
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• v.9 no.4
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• pp.251-259
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• 2018

In general, the charge storage characteristics and overall performance of electrochemical energy devices (such as lithiumion batteries and supercapacitors) significantly depends on the structural and geometrical factors of the electrodes' active materials. The most widely used active materials of electrochemical energy storage devices are based on carbons of various forms. Each carbon type has drawbacks and advantages when used as the electrode material. Studies have been recently carried out to combine different types of carbons, in particular nanostructured carbons, in order to overcome the structure-originated limitations and thus enhance the overall electrochemical performances. In this feature article, we report the recent progress on the development of this novel class of materials (multidimensional nanocarbons), and their applications for supercapacitors. Multidimensional nanocarbons include graphenes/carbon nanotubes (CNTs), CNTs/carbon films, CNTs/fullerenes, and ternary carbon nanostructures. Various applications using these multidimensional nanocarbons have been proposed and demonstrated in the literature. Owing to the recent extensive studies on electrochemical energy storage devices and considering that carbons are their most fundamental electrode materials, the number of reports on nanocarbons employed as electrodes of the electrochemical energy storage devices is rapidly increasing. Recently, numerous multidimensional nanocarbons have been designed, prepared, and utilized as electrodes of electrochemical capacitors or supercapacitors, which are considered next-generation energy devices owing to their unique merits compared to the conventional structures. In this review, we summarize the basic motivations, preparation methods, and resultant supercapacitor performances of each class of multidimensional nanocarbons published in the literature, focusing on recent reports.

• 한국신재생에너지학회:학술대회논문집
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• 2010.06a
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• pp.133.1-133.1
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• 2010

In this work, carbon black(CBs)-embed multi-walled carbon nanotubes (MWNTs) as conductive fillers for activated carbon(ACs)-based electrodes for supercapacitor were prepared by chemical reduction of oxidized MWNTs and CBs. The effect of CBs-MWNT composites on electrochemical performances of ACs-based electrodes were investigated as a function of CB-MWNT ratio. It was found that CBs-MWNTs composites were formed by the reduction reaction of the functional groups of oxidized MWNTs and CBs. It was resulted in the conjugation of CBs onto the MWNT having high surface area and aspect ratio, leading to the enhanced electrical properties of MWNTs. The electrochemical performances, such as current density, charge-discharge, and specific capacitance of the ACs/CBs-MWNT electrodes were higher than that of ACs/MWNTs and conventional ACs/CB electrodes, which was attributed to the synergistic effect of CBs-MWNTs as a conductive filler.

• 한국신재생에너지학회:학술대회논문집
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• 2011.05a
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• pp.159.2-159.2
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• 2011

In this study, we prepared the activated graphite nanofibers (A-GNFs) via chemical activation with KOH reagent. The effect of A-GNFs on the surface and textural properties of Ni-loaded graphite nanofibers (Ni/GNFs) was investigated by X-ray diffraction (XRD), transmission electron microscope (TEM), and Brunauer-Emmett-Teller (BET). The textural properties of samples were investigated by $N_2$/77K adsorption isotherms. The electrochemical performances were investigated by cyclic voltammetry. As a results, the electrochemical performances of Ni/GNFs were improved with usage of A-GNFs. This could be interpreted by the high specific surface area and large total pore volume of the A-GNFs.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.18 no.2
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• pp.142-147
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• 2005

In this work, a gel polymer electrolyte (GPE) was prepared using polyoxyalkylene glycol acrylate (POAGA) as a macromonomer LiCoO$_2$/GPE/graphite cells were prepared and their electrochemical properties were evaluated at various current densities and temperatures. The ionic conductivity of the GPE was more than 6.2${\times}$10$^{-3}$ S$.$$cm^{-1}$ / at room temperature. The GPE had good electrochemical stability up to 4.5 V vs. Li/Li$^{+}$. POAGA-based cells were showed good electrochemical performances such as rate capability, low-temperature performance, and cycleability. The cells, also, passed a safety test such as the overcharge and nail-penetration test.t.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.17 no.6
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• pp.608-614
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• 2004

The gel polymer electrolyte was prepared by radical polymerization using tetra(ethylene glycol) diacrylate and tri(ethylene glycol) dimethacrylate to investigate affect of the number of ethylene oxide. The gel polymer electrolyte showed good electrochemical stability up to 4.5 V vs. Li/Li and high ionic conductivity at various temperatures. The lithium-ion polymer batteries with the gel polymer electrolyte, tetra(ethylene glycol) diacrylate- and tri(ethylene glycol) dimethacrylate-based, also represented good electrochemical performances such as rate capability, low-temperature performances and cycleability. However, the cell with tri(ethylene glycol) dimethacrylate, which has three ethylene oxide, showed better electrochemical performance.

• Applied Chemistry for Engineering
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• v.16 no.5
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• pp.689-692
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• 2005

In order to improve the electrochemical performances of Li-ion batteries when spinel $LiMn_2O_4$ is employed as a cathode active material, binary conductive agents were prepared using two different particle-sized carbons like Super P Black and $Vulcan^{(R)}$ XC-72R. The electrochemical performances of the $LiMn_2O_4$ cell system using binary conductive agents were evaluated in terms of specific charge and discharge capacities and cycle life. The cell with binary conductive agent in the 3:7 weight ratios of Super P Black and $Vulcan^{(R)}$ XC-72R showed better electrochemical performances due to the proper combination of ionic diffusion rate and electric contact.