• Journal of Electrochemical Science and Technology
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• v.8 no.1
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• pp.1-6
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• 2017

The conductivity of the electrolyte used plays a critical role in the optimization of the performance of electrochemical double layer capacitors. However, when the difference in the conductivities of different electrolytes is not significant (only 10-20%), the conductivity has little effect on the capacitance. On the other, unlike the conductivity and viscosity of the electrolyte, the cation size directly influences the capacitance. Cyclic ions have a smaller effective radius than that of the corresponding acyclic ions because the acyclic alkyl groups have a greater number of conformational degrees of freedom, such as the rotational, bending, and stretching modes. Consequently, because of the smaller effective size of the cyclic ions, cells containing electrolytes with such ions exhibit higher capacitances than do those with their acyclic counterparts.

• Journal of Electrochemical Science and Technology
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• v.6 no.2
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• pp.59-64
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• 2015

Spherical Li₄Ti₅O₁₂ and Li₄Ti₅O₁₂ carbon nanotube (CNT) composites were synthesized using a colloid system. The electrochemical properties of the composites were thoroughly examined to determine their applicability as hybrid capacitor anodes. The electrical conductivity of the spherical Li₄Ti₅O₁₂-CNT composite was improved over that of the spherical Li₄Ti₅O₁₂ composite. The synthesized composites were utilized as the anode of a hybrid capacitor, which was assembled with an activated carbon (AC) positive electrode. The CNTs attached on the spherical Li₄Ti₅O₁₂ particles contributed to a 51% reduction of the equivalent series of resistance of the Li₄Ti₅O₁₂-CNTs/AC hybrid capacitor compared to the Li₄Ti₅O₁₂/AC hybrid capacitor. Moreover, the Li₄Ti₅O₁₂-CNTs/AC hybrid capacitor showed a larger capacitance than the Li₄Ti₅O₁₂/AC hybrid capacitor; specifically, the Li₄Ti₅O₁₂-CNT/AC hybrid capacitor showed 1.6 times greater capacitance at 40 cycles with a 10 mA cm⁻² loading current density.

• Korean Journal of Materials Research
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• v.11 no.11
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• pp.936-940
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• 2001

Spray pyrolysis is a favorable technique to form complex mixed-metal oxide powders with high purity in high temperature region. Manganese oxide powders were prepared by spray pyrolysis from an aqueous solution of $Mn(NO_3)_2$. Powders were formed in the temperature range of 500~$700^{\circ}C$ under the constant pressure of 300torr. All the powders have hydrous forms. When the temperature was increased, the size and the surface area of the particles decreased. An electrochemical capacitors were made with manganese oxide electrodes and KOH electrolyte. With the temperature decreased, capacitors showed high capacitance. Capacitor which was prepared with powders formed in the temperature $500^{\circ}C$ demonstrated specific capacitances as high as 83F/g.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.19 no.9
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• pp.849-854
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• 2006

In this study, the hybrid electrodes, composed of the activated carbon powders and $LiCoO_{2}$ powders, were prepared as a cathode for the high-capacitance type hybrid capacitor, and the electrochemical properties of the hybrid electrodes were examined in terms of the weight composition and the milling time of $LiCoO_{2}$ powders. The specific volumetric capacities were increased with increasing of the composition of $LiCoO_{2}$ powders in the hybrid electrodes. On the other hand the coin cell capacitors, using the hybrid electrodes with $LiCoO_{2}$ poweders milled for 200 h, have exhibited the lower internal resistivities and the better capacity retention after 100 charge-discharge cycle than those of the coin cell capacitors using the hybrid electrodes with raw $LiCoO_{2}$ powders.

• Bulletin of the Korean Chemical Society
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• v.31 no.12
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• pp.3697-3702
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• 2010

We demonstrate that vertically aligned carbon nanotubes can be synthesized directly on tantalum substrate via water-assisted chemical vapor deposition and evaluate their properties as electrochemical capacitors. The mean diameter of the carbon nanotubes was $7.1{\pm}1.5\;nm$, and 70% of them had double walls. The intensity ratio of G-band to D-band in Raman spectra was as high as 5, indicating good quality of the carbon nanotubes. Owing to the alignment and low equivalent series resistance, the carbon nanotube based supercapacitors showed good rate performance. Rectangular shape of cyclic voltammogram was maintained even at the scan rate of > 1 V/s in 1 M sulfuric acid aqueous solution. Specific capacitance was well-retained (~94%) even when the discharging current density dramatically increased up to 145 A/g. Consequently, specific power as high as 60 kW/kg was obtained from as-grown carbon nanotubes in aqueous solution. Maximum specific energy of ~20 Wh/kg was obtained when carbon nanotubes were electrochemically oxidized and operated in organic solution. Demonstration of direct synthesis of carbon nanotubes on tantalum current collectors and their applications as supercapacitors could be an invaluable basis for fabrication of high performance carbon nanotube supercapacitors.

• Korean Journal of Materials Research
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• v.32 no.7
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• pp.313-319
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• 2022

Double-layer capacitors (DLCs) are developed with high surface electrodes to achieve a high capacitance value. In the present work, the initial bulk concentration of 1 mol/m³ and 3 mol /m³ are selected to show the consequential effects on the performance of a double-layer capacitor. A 1D model of COMSOL Multiphysics has been developed to analyze the electric field and potential in cell voltage, the electric displacement field and polarization induced by the field, and energy density in a double-layer structure. The electrostatics and the electric circuit modes in COMSOL are used to simulate the electrochemical processes in the double-layer structure. The analytical analysis of a double-layer capacitor with different initial bulk concentrations is investigated by using Poisson-Nernst-Plank equations. From the simulation results, the differential capacitance changes as a function of compact layer thickness and initial bulk concentration. The energy density varies with the differential capacitance and voltage window. The values of energy density are dominated by the interaction of ions in the solution and electrode surface.

• Carbon letters
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• v.12 no.4
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• pp.252-255
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• 2011

Carbon-based electric double-layer capacitors are being evaluated as potential energy-storage devices in an expanding number of applications. In this study, samples of carbon black (CB) treated at different temperatures ranging from $650^{\circ}C$ to $1100^{\circ}C$ were used as electrodes to improve the efficiency of a capacitor. The surface properties of the heat-treated CB samples were characterized by X-ray photoelectron spectroscopy and X-ray diffraction. The effect of the heat-treatment temperature on the electrochemical behaviors was investigated by cyclic voltammetry and in galvanostatic charge-discharge experiments. The experimental results showed that the crystallinity of the CBs increased as the heat-treatment temperature increased. In addition, the specific capacitance of the CBs was found to increase with the increase in the heat-treatment temperature. The maximum specific capacitance was 165 $F{\cdot}g-1$ for the CB sample treated at $1000^{\circ}C$.

• Journal of the Korean institute of surface engineering
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• v.55 no.2
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• pp.84-90
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• 2022

With the growing interest in energy storage and conversion systems including secondary batteries, capacitors, and water electrolysis, various electrode materials are being developed to improve the energy efficiency. Among them, graphene is regarded as one of the promising candidates owing to its exceptional properties - large surface area, and excellent electrical conductivity. Herein, we report a facile one-step electrochemical approach to synthesize exfoliated graphene/Fe oxide compound. The effect of experimental conditions - the types of applied voltage, kinds of counter electrodes, acidity of electrolyte on the synthesis of graphene/Fe oxide compound is investigated.

• Journal of the Korean Electrochemical Society
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• v.20 no.1
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• pp.13-17
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• 2017

In this study, we studied the organic electrolyte application to electrochemical capacitor for high operation voltage. For high operating voltage, 5 wt % of gamma butyroloctone (GBL) was added in the bare electrolyte. During the cycle performance, stable SEI layers were formed by reductive decomposition of additive GBL. As a result, columbic efficient of 1M $SBPBF_4$ in EC:DMC(1:1) with GBL composite was enhanced to 70% after the 2000th cycle at voltage range 0-3.5 V. Additionally, SEI layer protected the surface of electrode and prevent the side-reaction between electrolyte to electrode.

• Korean Chemical Engineering Research
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• v.53 no.2
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• pp.131-136
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• 2015

The nanostructural graphene/vanadium oxide (graphene/$V_2O_5$) composite with enhanced capacitance was synthesized by the electro-deposition in 0.5 M $VOSO_4$ solution. The morphology of composites was characterized using scanning electron microscopy (SEM), x-ray diffraction pattern (XRD), and x-ray photoelectron spectroscopy (XPS). The oxidation states of the electro-deposited vanadium oxide was found to be $V^{5+}$ and $V^{4+}$. The morphology of the prepared graphene/$V_2O_5$ composite exhibits a netlike nano-structure with $V_2O_5$ nanorods in about 100 nm diameter, which could lead a better contact between electrolyte an electrode. The composite with a deposition time of 4,000 s exhibits the specific capacitance of $854mF/cm^2$ at a scan rate of 20 mV/s and the capacitance retention of 53% after 1000 CV cycles.