• Advanced Composite Materials
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• v.17 no.2
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• pp.167-175
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• 2008

Vapor grown carbon fibers (VGCF) were treated with atmospheric plasma enhancing the surface area in order to improve the bonding to the matrix in epoxy composites. The changes in the mechanical properties of VGCF/epoxy nanocompostes, such as tensile modulus and tensile strength were investigated in this study. VGCF with and without atmospheric plasma treatment for surface modification were used in this investigation. The interdependence of these properties on the VGCF contents and interfacial bonding between VGCF/epoxy matrix were discussed. The mechanical properties of atmospheric plasma treated (APT) VGCF/epoxy were compared with raw VGCF/epoxy. The tensile strength of APT VGCF/epoxy nanocomposites showed higher value than that of raw VGCF. The tensile strength was increased with atmospheric plasma treatment, due to better adhesion at VGCF/epoxy interface. The tensile modulus of raw VGCF and APT VGCF/epoxy matrix were of the similar value. The dispersion of the VGCF was investigated by scanning electron microscopy (SEM), SEM micrographs showed an excellent dispersion of VGCF in epoxy matrix by ultrasonic method.

• Journal of the Korean Applied Science and Technology
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• v.24 no.3
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• pp.264-271
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• 2007

Effect of dispersion methods for Vapor Grown Carbon Fibers (VGCF) in epoxy caused the change in mechanical properties of VGCF/epoxy nanocomposites, such as tensile modulus and tensile strength. The influence of VGCF types - atmospheric plasma treated (APT) VGCF and raw VGCF - and their contents was discussed in detail. Treating VGCF with atmospheric plasma enhanced the surface energy, therefore improved the bonding strength with epoxy matrix. Two different methods used to disperse VGCF were ultrasonic and mechanical homogenizer methods. When using dispersion solutions, the VGCF demonstrated good dispersion in ethanol in both homogenizer and ultrasonic method. The uniform dispersion of VGCF was investigated by scanning electron microscopy (SEM) which showed well-dispersion of VGCF in epoxy matrix. The tensile modulus of raw VGCF/epoxy nanocomposites obtained by ultrasonic method was higher than that of one obtained by homogenizer method. APT VGCF/epoxy nanocomposites showed higher tensile strength than that of raw VGCF/epoxy nanocomposites.

• Journal of the Korean Electrochemical Society
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• v.7 no.3
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• pp.143-147
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• 2004

An investigation upon the characterization of MCMB anodes with different vapor grown carbon fiber (VGCF) content for application in lithium polymer battery(LPB) was carried out. When VGCF material was used as conducting agent with MCMB active material, the impedance and the initial coulombic efficiency of test cells were found to decrease with the increasing amount of VGCF. On the other hand, as a function of added VGCF the discharge capacity and the utilization linearly with increased. Impedance of test cell with MCMB anode containing $6wt\%$ VGCF exhibited the lowest value whereas the impedance of $8wt\%$ VUF contained anode was similar to that of MCMB anode without VGCF. Interestingly, $6wt\%$ VUF contained anode showed the best battery characteristics. Internal resistance and rate capacity of the cell were. respectively, $0.918{\Omega}\;at\;25C\;and\;93\%$ at 2C. Generally, rate capability and the cycleability of MCMB based test cells with $4\~6wt\%$ VGCF content exhibited better results than the other cells. In the case of $6wt\%$ VGCF containing anode, the discharge capacity of the cell faded slowly with an ultimate charge-discharge cycling capacity of 178mAh/g at the 100th cycle. Thereafter, the discharge capacity faded negligibly and the utilization of the cell at the 100th cycle was more than $90\%$. The effect of addition of VGCF is discussed in detail.

• Journal of the Korean Electrochemical Society
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• v.27 no.3
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• pp.88-96
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• 2024

Lithium metal has garnered attention as a promising anode active material thanks to its high specific capacity, energy density, and the lowest reduction potential. However, the formation of dendrites, dendritic crystals that arise during the charge and discharge process, has posed safety and lifetime stability challenges. To resolve this, our study has introduced a novel separator design. This separator features a composite coating of vapor-grown carbon fiber, a conductive material in nanofibers, and silver. We have meticulously studied the impact of this innovative separator on the electrochemical properties of the lithium metal anode, unveiling promising results. To confirm the synergistic effect of VGCF and Ag, a separator with no surface treatment and a separator with only VGCF coated on one side were prepared and compared with the Ag-VGCF-separator. In the case of the bare separator, the Li metal surface is covered with dendrites during the initial charge and discharge process. In contrast, both the VGCF-separator and the Ag-VGCF-separator show Li precipitation inside the conductive coating layer coated on the separator surface. Additionally, the Ag-VGCF-separator showed a more uniform precipitate shape than the VGCF-separator. As a result, the Ag-VGCF-separators show improved electrochemical properties compared to the bare separators and the VGCF-separators.

• Advanced Composite Materials
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• v.18 no.3
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• pp.221-232
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• 2009

The allylamine plasma treatment is used to modify the surface properties of vapor grown carbon fibers (VGCF). It is to improve the interfacial bonding between the VGCF and epoxy matrix. The allylamine plasma process was performed by batch process in a vacuum chamber, using gas injection followed by plasma discharge for the durations of 20, 40 and 60 min. The interdependence of mechanical properties on the VGCF contents, treatment time and interfacial bonding between VGCF/ep was investigated. The interfacial bonding between VGCF and epoxy matrix was observed by scanning electron microscopy (SEM) micrographs of nanocomposites fracture surfaces. The changes in the mechanical properties of VGCF/ep, such as the tensile modulus and strength were discussed. The mechanical properties of allylamine plasma treated (AAPT) VGCF/ep were compared with those of raw VGCF/ep. The tensile strength and modulus of allyamine plasma treated VGCF40 (40 min treatment)/ep demonstrated a higher value than those of other samples. The mechanical properties were increased with the allyamine plasma treatment due to the improved adhesion at VGCF/ep interface. The modification of the carbon nanofibers surface was observed by transmission electron microscopy (TEM). SEM micrographs showed an excellent dispersion of VGCF in epoxy matrix by ultrasonic method.

• Polymer(Korea)
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• v.30 no.1
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• pp.85-89
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• 2006

The effect of vapor grown carbon fiber (VGCF) contents on electrical and rheological properties of VGCF filled polyphenylene sulfide (PPS) composites prepared through melt mixing using a twin screw exruder was studied. This method was proved to be quite effective to produce good dispersion of VGCF in the matrix even for highly filled PPS. From the dependence of the electrical conductivity on VGCF content, the percolation phenomena began to occur above $10\;wt\%$. While there is only a marginal increase of viscosity for 1 and $5\;wt\%$ VGCF filled PPS, the composites containing $10\;wt\%$. While VGCF showed abrupt increase in viscosity as well as flattening of frequency vs modulus curve, indicating a transition from a liquid-like to a solid-like behavior due to the creation of VGCF network. This result agrees well to the fact that the network formation in the composite can be composite by rheological property dependence on filler content as well as by electrical conductivity measurement.

• Journal of the Korean Society for Precision Engineering
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• v.24 no.8 s.197
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• pp.21-24
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• 2007

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.11a
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• pp.421-424
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• 2000

We have examined the impedance characteristics and the rate characteristics of LPB. As results, the impedance of LPB decreased with increased pressing rate of electrodes, adding amounts of PVdF and VGCF. And the rate characteristics of LPB increased with the a increase of pressure-rate, PVdF and VGCF contents. The rate characteristics of LPB was improved by pressing of electrode and adding of VGCF content. And specific capacity of anode was increased with adding amounts of PVdF. Higher pressing rate of electrodes, higher adding amounts of PVdF and VGCF was necessitated good rate characteristics for lithium polymer battery.

• Korean Chemical Engineering Research
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• v.46 no.1
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• pp.94-98
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• 2008

In order to improve the specific capacitance of amorphous hydrous manganese oxide ($MnO_2$) for supercapacitors, it is made into composites with vapour-grown carbon nanofibers (VGCF) having the VGCF ratio as 40 wt% in the composites. The electrochemical properties of these composites are investigated in 1.0 M $Na_2SO_4$ by cyclic voltammetry (CV), impedance measurements and chronopotentiometric charger/discharger. The composite with 40 wt% VGCF shows the superior electrochemical performance, whose specific capacitance (based on the mass of $MnO_2$, $0.8mg/cm^2$) is 380 F/g at 20 mV/s and 230 F/g at 500 mV/s. Also, the cycle-life testing of this electrode carried out for 3,000 charge/discharge cycles at $2.0mA/cm^2$ shows 97% capacitance retention.

• Korean Chemical Engineering Research
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• v.44 no.6
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• pp.563-571
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• 2006

Vapor grown carbon fiber (VGCF) nano-materials such as carbon nanotubes and carbon nanofibers were directly grown on the surface of the stainless steel mesh pre-treated by reduction. The reduction of the stainless steel mesh by hydrogen formed small catalytic particles and large particles with bi-modal distribution on the metal surface. When the VGCFs were synthesized on the reduced mesh, carbon nanotubes (CNTs) were dominantly grown from the small catalytic particles without supplying hydrogen gas. However, carbon nanofibers (CNFs) were dominantly grown from the large catalytic particles with hydrogen.