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Lee Y.J.,Seoul National University | Jung J.C.,Seoul National University | Park S.,Seoul National University | Seo J.G.,Seoul National University | And 4 more authors.
Current Applied Physics | Year: 2010

Carbon aerogel was prepared by polycondensation of resorcinol and formaldehyde using sodium carbonate as a catalyst with a resorcinol to catalyst ratio of 500. Co-doped carbon aerogels were then prepared by an impregnation method with a variation of cobalt content (1, 3, 5, 7, 10, and 15 wt.%), and their performance for supercapacitor electrode was investigated by measurement of specific capacitance in 1 M H2SO4 electrolyte at a scan rate of 10 mV/s. Among the samples prepared, 7 wt.% Co-doped carbon aerogel showed the highest capacitance (100 F/g) and stable cyclability. The enhanced capacitance of Co-doped carbon aerogel was attributed to the faradaic redox reactions of cobalt oxide. On the basis of this result, 7 wt.% Cu-, Fe-, Mn-, and Zn-doped carbon aerogels were also prepared by an impregnation method for use as a supercapacitor electrode. Among the metal-doped carbon aerogels, Mn-doped carbon aerogel showed the highest capacitance (107 F/g) while Cu- and Fe-doped carbon aerogels exhibited the most stable cyclability. © 2009 Elsevier B.V. All rights reserved.


Lee Y.J.,Seoul National University | Jung J.C.,Seoul National University | Yi J.,Seoul National University | Baeck S.-H.,Inha University | And 2 more authors.
Current Applied Physics | Year: 2010

Carbon aerogels were prepared by polycondensation of resorcinol with formaldehyde using sodium carbonate as a catalyst in ambient conditions, and they were used as an electrode of electrical double-layer capacitor. The effect of resorcinol to catalyst ratio (R/C ratio) on volume shrinkage, BET surface area, and electrochemical property of carbon aerogels was investigated by changing R/C ratio from 50 to 2000. In order to minimize volume shrinkage, solvent exchange was performed with acetone at 50 °C for 1 day. Volume shrinkage was <2% after 2-day gelation in the absence of CO2 supercritical drying. BET surface area was strongly dependent on R/C ratio. Carbon aerogel prepared at R/C ratio of 500 showed the highest BET surface area (706 m2/g) with average pore diameter of 10.9 nm. Electrochemical property of carbon aerogels as an electrode of electrical double-layer capacitor was investigated by cyclic voltammetry measurement. Specific capacitance of carbon aerogel prepared at R/C ratio of 500 was found to be 81 F/g in 1 M H2SO4 electrolyte at the scan rate of 10 mV/s. © 2009 Elsevier B.V. All rights reserved.


Lee Y.J.,Seoul National University | Jung J.C.,Myongji University | Park S.,Seoul National University | Seo J.G.,Seoul National University | And 4 more authors.
Journal of Nanoscience and Nanotechnology | Year: 2011

Carbon aerogel was prepared by polycondensation of resorcinol with formaldehyde using sodium carbonate as a catalyst in ambient conditions. Nano-sized Ni-doped carbon aerogel was then prepared by a precipitation method in an ethanol solvent. In order to elucidate the effect of nickel content on electrochemical properties, Ni-doped carbon aerogels (21, 35, 60, and 82 wt%) were prepared and their performance for supercapacitor electrode was investigated. Electrochemical properties of Ni-doped carbon aerogel electrodes were measured by cyclic voltammetry at a scan rate of 10 mV/sec and charge/discharge test at constant current of 1 A/g in 6 M KOH electrolyte. Among the samples prepared, 35 wt% Ni-doped carbon aerogel (Ni/CA-35) showed the highest capacitance (110 F/g) and excellent charge/discharge behavior. The enhanced capacitance of Ni-doped carbon aerogel was attributed to the faradaic redox reactions of nano-sized nickel oxide. Moreover, Ni-doped carbon aerogel exhibited quite stable cyclability, indicating long-term electrochemical stability. Copyright © 2011 American Scientific Publishers All rights reserved.


Lee Y.J.,Seoul National University | Jung J.C.,Myongji University | Park S.,Seoul National University | Seo J.G.,Seoul National University | And 4 more authors.
Current Applied Physics | Year: 2011

To investigate the effect of preparation method on electrochemical properties, Mn-doped carbon aerogels were prepared using monolith carbon aerogel and carbon aerogel powder. For this purpose, Mn-doped carbon aerogels (Mn-doped monolith carbon aerogel and Mn-doped carbon aerogel powder) were prepared by two different wet impregnation methods. Electrochemical properties of Mn-doped carbon aerogel electrodes were investigated by cyclic voltammetry and galvanostatic charge/discharge measurements. Compared to carbon aerogel, Mn-doped carbon aerogels exhibited the enhanced specific capacitance. The improved performance of Mn-doped carbon aerogels came from pseudocapacitive characteristics of manganese oxide. Among various Mn-doped monolith carbon aerogels, 18.8 wt% Mn-doped monolith carbon aerogel showed the highest specific capacitance. It was also revealed that Mn-doped monolith carbon aerogel retained highly dispersed manganese oxide particles on carbon aerogel matrix compared to Mn-doped carbon aerogel powder. Therefore, Mn-doped monolith carbon aerogel showed higher specific capacitance than Mn-doped carbon aerogel powder. © 2010 Elsevier B.V. All rights reserved.


Lee Y.J.,Seoul National University | Park S.,Seoul National University | Seo J.G.,Seoul National University | Yoon J.R.,Samwha Capacitor Co. | And 2 more authors.
Current Applied Physics | Year: 2011

Carbon aerogel was prepared by polycondensation of resorcinol with formaldehyde using sodium carbonate as a catalyst in ambient conditions. Nano-sized Ni-doped carbon aerogel was then prepared by a precipitation method in an ethanol solvent. In order to elucidate the effect of Ni content on electrochemical properties, nano-sized Ni-doped carbon aerogels with different Ni content (21, 35, 60, and 82 wt%) were prepared and their performance for pseudo-capacitive supercapacitor electrode was investigated. Electrochemical properties of nano-sized Ni-doped carbon aerogel electrodes were measured by cyclic voltammetry at a scan rate of 10 mV/s and charge/discharge test at constant current of 1 A/g in 6 M KOH electrolyte. Among the samples prepared, 35 wt% nano-sized Ni-doped carbon aerogel (Ni/CA-35) showed the highest capacitance (120 F/g) and excellent charge/discharge behavior. The enhanced capacitance of nano-sized Ni-doped carbon aerogel was attributed to the faradaic redox reactions of nano-sized Ni oxide. On the basis of this result, ca. 35 wt% Co-, Cu-, Fe-, and Mn-doped carbon aerogels were also prepared by a precipitation method. Among the nano-sized metal-doped carbon aerogels, Mn-doped carbon aerogel (Mn/CA-34) showed the highest capacitance (141 F/g). © 2010 Elsevier B.V. All rights reserved.


Yoon J.R.,SAMWHA CAPACITOR Co. | Shin D.S.,SAMWHA CAPACITOR Co. | Jeong D.Y.,Inha University | Lee H.Y.,Korea University
Transactions on Electrical and Electronic Materials | Year: 2012

BaTiO 3 based multilayer ceramic capacitors with Ni electrodes can be explained as 2-2 composites with different thermal expansion coefficient and sintering behaviors. To achieve the high capacitance and reliability of MLCCs, a homogenous Ni electrode configuration with high connectivity is required. We controlled the heating rates during sintering to achieve densification by suppressing grain growth. Experimental results revealed that a large heating rate gave high connectivity of Ni electrode, high capacitance, small dissipation factor, high breakdown voltage, and high reliability of MLCC chips. © 2012 KIEEME. All rights reserved.


Jeong D.-Y.,Inha University | Lee S.-I.,Pennsylvania State University | Lee H.-Y.,Myongji University | Kim M.-K.,SamWha Capacitor Co. | Yoon J.-R.,SamWha Capacitor Co.
Japanese Journal of Applied Physics | Year: 2013

The influence of glass power morphology on the electrical and microstructural properties of BaTiO3-based multilayer ceramic capacitors (MLCCs) was investigated to enhance the reliability of MLCCs. For a sintering additive, glass particles of different sizes and shapes were prepared by jetmilling and RF plasma treatment. Plasma treatment decreased the glass particle size and transformed the irregular shape of glass particles into homogeneous spherical shapes. It was found that MLCCs sintered with plasma-treated glass powder have a more homogeneous microstructure, a clear core-shell structure, a more stable capacitance against voltage and temperature changes, and a higher degradation resistance. It is inferred that nanosized spherical glass powder prepared by plasma treatment helps so-called magic dopants. such as rare-earth elements to be distributed homogeneously around the BaTiO3 particles. © 2013 The Japan Society of Applied Physics.


Lee B.G.,Samwha Capacitor Co. | Yoon J.R.,Samwha Capacitor Co.
Journal of Electrical Engineering and Technology | Year: 2012

Spinel-Li 4Ti 5O 12 was successfully synthesized by a solid-phase method at 800, 850, and 900? according to the Li 4Ti 5O 12 cubic spinel phase structure. To achieve higher EDLC energy density with the Li 4Ti 5O 12, the negative electrode of the hybrid supercapacitor was studied in this work. The electrochemical performances of the hybrid supercapacitor and EDLC were characterized by constant current discharge curves, c-rate, and cycle performance testing. The capacitance (1st cycle) of the hybrid supercapacitor and EDLC was 209 and 109 F, respectively, which is higher than EDLC. The capacitance of the hybrid supercapacitor decreases from 209 F to 101 F after 20 cycles when discharged at several specific current densities ranging from 1 to 10 A. In contrast, capacitance of the EDLC hardly decreases after 20 cycles. Results show that hybrid supercapacitor benefits from the high rate capability of supercapacitor and high capacity of the battery. Findings also prove that the hybrid supercapacitor is an energy storage device where the supercapacitor and the Li ion secondary battery coexist in one cell system.


Lee B.-G.,Seoul National University of Science and Technology | Lee B.-G.,Samwha Capacitor Co. | Ahn H.-J.,Seoul National University of Science and Technology | Yoon J.-R.,Samwha Capacitor Co.
Journal of Nanoscience and Nanotechnology | Year: 2016

We report two types of spinel Li4Ti5O12 synthesized from the mixtures of two different nano-sized Ti precursors (TiO(OH)2 and TiO2) using microwave heating. The mixed precursors were heated at various temperatures ranging from 450 to 750°C using microwave heating processing. Spinel Li4Ti5O12 prepared from TiO(OH)2 as a Ti precursor exhibits lower synthesis temperature of 550°C than Li4Ti5O12 prepared from TiO2. Two types of spinel Li4Ti5O12 obtained from TiO(OH)2 and TiO2 were characterized using X-ray diffraction, particle size distribution, and scanning electron microscopy. Hybrid capacitors to evaluate the electrochemical performance of spinel Li4Ti5O12 were fabricated using activated carbon as a cathode material. TiO(OH)2 has the advantage of low-temperature synthesis in comparison with rutile or anatase phase TiO2, because TiO(OH)2 possesses a high concentration of defects in the structure. As a result, the rate capability of the hybrid capacitor improved with the decreasing particle size of the Li4Ti5O12 prepared from TiO(OH)2 owing to the increasing contact area between electrode and electrolyte, as well as reduced diffusion path of lithium ions. In this study, we demonstrated that the high-rate performance and long-term cycle stability of Li4Ti5O12 obtained from TiO(OH)2 for hybrid capacitors. The presented hybrid capacitor could be a competitive candidate for use in promising energy storage devices. Copyright © 2016 American Scientific Publishers All rights reserved.


Kim J.H.,Samwha Capacitor Co. | Yoon J.R.,Samwha Capacitor Co.
Journal of Advanced Ceramics | Year: 2013

The electrical characteristics of hybrid super capacitor were evaluated by synthesizing LTO (Li4Ti5O12) using TiO2 having a hydrogen titanate nanowire form. Preparation of the hydrogen titanate nanowire was implemented by using TiO2 having size of 60 nm and NaOH, and performing synthesis at 70 °C for 6 h with a sonochemical method. LTO compound was synthesized at 150 °C for 36 h and at 180 °C for 36 h respectively by using the hydrogen titanate nanowire and LiOH·H2O as starting materials with a hydrothermal method. The final LTO compound was synthesized at 700 °C for 6 h using a solid-state method. As a result of manufacturing the hybrid super capacitor using LTO synthesized at 180 °C for 36 h with the hydrothermal method, a capacity of 198 mA·h/g has been achieved compared to a theoretical capacity of 172 mA·h/g of existing LTO, and thus, the capacity has been increased by about 13%. Further, such excellent cycle performance has ensured its possibility as a high-capacity capacitor. © 2013, The Author(s).

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