• Applied Chemistry for Engineering
• /
• v.33 no.1
• /
• pp.58-63
• /
• 2022

Graphite has been used as an anode material for lithium-ion batteries for the past 30 years due to its low de-/lithiation voltage, high theoretical capacity of 372 mAh/g, low price, and long life properties. Recently, all-solid-state lithium-ion batteries (ASSLB), which are composed of inorganic solid materials with high stability, have received great attention as electric vehicles and next-generation energy storage devices, but research works on graphite that works well for ASSLB systems are insufficient. Therefore, we induced the performance improvement of ASSLB anode electrode graphite material by removing the amorphous carbon present in the carbon material surface, acting as a resistive layer from the graphite. As a result of X-ray diffraction (XRD) analysis using heat treated graphite in air at 400, 500, and 600 ℃, the full width at half maximum (FWHM) at (002) peak was reduced compared to that of bare graphite, indicating that the crystallinity of graphite was improved after heat treatment. In addition, the discharge capacity, initial coulombic efficiency (ICE) and cycle stability increased as the crystallinity of graphite increased after heat treatment. In the case of graphite annealed in air at 500 ℃, the high capacity retention rate of 331.1 mAh/g and ICE of 86.2% and capacity retention of 92.7% after 10-cycle measurement were shown.

• Membrane Journal
• /
• v.33 no.4
• /
• pp.211-221
• /
• 2023

This study presents a comprehensive study on the synthesis and characterization of PVI-PGMA/LiTFSI polymeric membrane electrolytes and CxNy-C flexible electrodes for energy storage applications. The dual-functional PVI-PGMA copolymer exhibited excellent ionic conductivity, with the PVI-PGMA73/LiTFSI200 membrane electrolyte achieving the highest conductivity of 1.0 × 10^-3 S cm^-1. The electrochemical performance of the CxNy-C electrodes was systematically investigated, with C3N2-C demonstrating superior performance, achieving the highest specific capacitance of 958 F g^-1 and lowest charge transfer resistance (R_ct) due to its highly interconnected hybrid structure comprising nanowires and polyhedrons, along with binary Co/Ni oxides, which provided abundant redox-active sites and facilitated ion diffusion. The presence of a graphitic carbon shell further contributed to the enhanced electrochemical stability during charge-discharge cycles. These results highlight the potential of PVI-PGMA/LiTFSI polymeric membrane electrolytes and CxNy-C electrodes for advanced energy storage devices, such as supercapacitors and lithium-ion batteries, paving the way for further advancements in sustainable and high-performance energy storage technologies.

• Journal of Digital Contents Society
• /
• v.18 no.6
• /
• pp.1199-1205
• /
• 2017

Global energy consumption is rapidly increasing yearly due to drastic industrial advances, requiring the development of new energy storage devices. For this reason, supercapacitors with fast charge-discharge, long life cycle and high power density is getting attention, and have been considered as one of the potential energy storage systems. In this research, we developed a supercapacitor that consists of amorphous manganese oxide($MnO_2$) electrodes deposited onto carbon cloth substrates using the hydrothermal method. The Fe-doped amorphous $MnO_2$ samples were characterized by X-ray diffraction(XRD), Energy Dispersive X-ray spectroscopy(EDX), as well as scanning electron microscopy(SEM). The electrochemical analysis of the prepared samples were performed using cyclic voltammetry and galvanostatic charge-discharge measurements in 1M $Na_2SO_4$ electrolyte. The test results demonstrate that the supercapacitor based on the Fe-doped amorphous $MnO_2$ electrodes has a specific capacitance as high as 163F/g at 1A/g current density, and good cycling stability of 87.34% capacitance retention up to 1000 cycles.

• Korean Chemical Engineering Research
• /
• v.51 no.4
• /
• pp.411-417
• /
• 2013

To use as an anode material of lithium secondary battery, graphite-silicon composite powders are prepared by ball-milling with silicon nanoparticles (average diameter 100 nm, 0~50 wt%) and graphite powder (average diameter $15{\mu}m$) and their electrochemical properties are examined. As the silicon content increases, the graphite becomes smaller by the ball-milling and amorphous phase appears whereas the silicon do not suffer the change of nanocrystalline phases and embeds within the amorphous phase of graphite. Cyclic voltammetry at low scan rate reveals that typical oxidation peaks of graphite and silicon appear at 0.2~0.35 and 0.55~0.6 V, respectively, with higher reversibility for repeated cycles. In contrast, the high-scan-rate redox behavior is very irreversible for repeated cycles. High irreversible capacity is exhibited in the initial charging-discharging cycles, but it diminishes as the cycle number increases. The saturated discharge capacity achieves about 485 mAh $g^{-1}$ at 50th cycle for the composite of Si 20 wt%. This is due to the formation of amorphous graphite morphology by the adequate composition (C:Si=8:2 w/w), which efficiently buffers the volume change during alloying/dealloying between silicon and lithium.

• Korean Chemical Engineering Research
• /
• v.57 no.1
• /
• pp.118-123
• /
• 2019

In this study, the electrochemical characteristics of Graphite/Silicon/Pitch anode composites were analyzed to improve the low theoretical capacity of graphite as a lithium ion battery. The Graphite/Silica composites were synthesized by bonding silica onto polyvinylpyrrolidone coated graphite. The surface of used silica was treated with (3-Aminopropyl)triethoxysilane(APTES). Graphite/Silicon/Pitch composites were prepared by carbonization of petroleum pitch, the fabrication processes including the magnesiothermic reduction of nano silica to obtain silicon and varying the mass ratio of silica. The Graphite/Silicon/Pitch composites were analysed by XRD, SEM and XRD. Also the electrochemical performances of Graphite/Silicon/Pitch composite as the anode of lithium ion battery were investigated by constant current charge/discharge, rate performance, cyclic voltammetry and electrochemical impedance tests in the electrolyte of $LiPF_6$ dissolved in organic solvents (EC:DMC:EMC=1:1:1 vol%). The Graphite/Silicon/Pitch anode composite (silica 28.5 in weight) has better capacity (537 mAh/g). The cycle performance has an excellent capacity retention to 30th cycle of 95% and the retention rate capability of 98% in 0.1 C/0.2 C.

• Journal of the Korea Society of Computer and Information
• /
• v.6 no.2
• /
• pp.8-13
• /
• 2001

We demonstrate a pulsed CO$_2$laser with long pulse duration of millisecond order in the low pressure less than 30 Torr. A new power supply for our laser system switches the voltage of AC power line(60㎐) directly. The power supply doesn't need elements such as a rectified bridge, energy-storage capacitors. and a current-limiting resistor in the discharge circuit. In order to control the laser output power, the pulse repetition rate is adjusted up to 60㎐ and the firing angle of SCR gate is varied from 30˚ to 150˚. A ZCS(Zero Crossing Switch) circuit and a PIC one-chip microprocessor are used to control the gate signal of SCR precisely. The maximum laser output is 23W at the total pressure of 18 Torr, the pulse repetition rate of 60㎐, and SCR gate firing angle of 90˚. In addition, the obtained laser pulse width is approximately 3㎳(FWHM)

• Journal of the Institute of Electronics Engineers of Korea SC
• /
• v.42 no.3 s.303
• /
• pp.63-70
• /
• 2005

The electrodeless lamps using the induction discharge have a long lifetime and a high tolerance for the variable output conditions of a ballast since they don't need the electrodes. This paper proposed two novel dimming algorithms for the Electrodeless lamps and described the resonant inverter adopted the proposed methods. The proposed dimming algorithms are based on the conventional burst dimming method which is normally adopted for LCD back-lights. One of the proposed algorithms is a improved burst dimming method, which controls the illumination by duty ratio of $5\%$ and its control circuit is formed by simple digital logics. The other algorithm is a burst PWM average duty ratio control method, which controls the illumination by duty ratio of $1\%$ and its control circuit is formed by more complex digital logics than the first method. To verify the validity of the proposed dimming methods, a prototype experimental setup for 100W Electrodeless lamps is carried out and its results are presented in this paper.

• Applied Chemistry for Engineering
• /
• v.5 no.1
• /
• pp.44-53
• /
• 1994

A study on the iron electrode which is a good material for alkaline battery because of its superior characteristics including high theoretical capacity density, low toxicity, low cost and inexhaustible supply was performed to develop high performance nickel-iron secondary battery. The characteristics of chrage-discharge reaction were examined by cyclic voltammetry technique SEM and XRD analysis. The capacity of the test electrodes was determined by the costant current charge-discharge method. It was found that the purity and particle size of iron material were the major determinant factors of electrode capacity. With the addition of $Na_2S$ into the electrolyte the capacity of electrode was increased about 20 % caused by the prevention of passivation and the increase of hydrogen overpotential. The stability and capacity of electrode were increased with the use of Ni-fibrex and foamed Ni collectors and also depended on the sintering temperature. The capacity of electrode was 350 mAh/g(0.2 C) which corresponded to 36% utility.

• Journal of the Korean Electrochemical Society
• /
• v.17 no.3
• /
• pp.187-192
• /
• 2014

In this article, we report the fabrication and characterization of $CNT/Co_3O_4$ nanocomposite for lithium ion batteries. We expected that the composition with CNT is effective method to compensate for the low electronic conductivity of $Co_3O_4$ and suppress the stress from phase transition of $Co_3O_4$ during cycling. $CNT/Co_3O_4$ nanocomposites were composed of nano-sized $Co_3O_4$ particles, which were homogeneously distributed on the surface of CNTs. The $CNT/Co_3O_4$ electrode presented higher capacity than commercial graphite, good rate capability and stable cyclic performance. This implies that the $CNT/Co_3O_4$ could be a promising anode material for lithium ion batteries.

• The Transactions of the Korean Institute of Power Electronics
• /
• v.13 no.4
• /
• pp.247-256
• /
• 2008

Regenerative energy generated by regenerative braking of DC traction can cause the system malfunction or damage to the rectifier, or malfunction of the power conversion device in power supply system by DC Line voltage rise in feeder line. Regenerative energy storage system using super capacitor is one of the ways to stabilize DC line voltage. In this paper, energy storage system of DC traction system using super-capacitor bank is implemented and using the field measurement data of the station N and the station S on the Line 2, the operation characteristics of line voltage caused by regenerative energy of electric trains are verified. Also, charge/discharge characteristics of super capacitor are verified as well. Thus, we can verify the operation characteristics of super-capacitor bank for regenerative energy storage system installed in DC Traction. And if we can use field measurement data of DC line voltage, we have obtained cost reduction. The stabilization of the system will be improved by measuring the operation characteristics of regenerative energy storage system in certain section operated by DC traction and predicting the capacity and lifetime of super-capacitor.