• Journal of the Korean Electrochemical Society
• /
• v.17 no.3
• /
• pp.156-163
• /
• 2014

In this study, we tried to improve the cycling performance of lithium-ion batteries by suppressing decomposition of the electrolyte solution containing fluorsilane-based additive. Trifluoropropyltrimethoxysilane was electrochemically oxidized and reduced prior to the decomposition of the liquid electrolyte composed of lithium salt and carbonate-based organic solvent. Thus, the stable solid electrolyte interphase (SEI) layer on both negative electrode and positive electrode was formed, and it was confirmed that the cycling performance of lithium-ion batteries assembled with electrolyte solution containing 5 wt.% trifluoropropyltrimethoxysilane was the mostly enhanced. The products formed on electrodes were analyzed by the SEM and XPS analysis, and it was demonstrated that trifluoropropyltrimethoxysilane can be one of the promising SEI-forming additives.

• Membrane Journal
• /
• v.26 no.2
• /
• pp.141-145
• /
• 2016

Polymer electrolyte membranes (PEMs) are key components to determine electrochemical fuel cell performances, in addition to electrode materials. The PEMs need to satisfy selective transport behaviors to small molecules including gases and protons; the PEMs have to transport protons as fast as possible, while they should act as hydrogen barriers, since the permeated gas induces the thermal degradation of cathode catalyst, resulting in rapid electrochemical reduction. To date, limited tools have been used to measure how fast hydrogen gas permeates through PEMs (e.g., Constant volume/variable Pressure (time-lag) method). However, most of the measurements are conducted under vacuum where PEMs are fully dried. Otherwise, the obtained hydrogen permeance is easily changeable, which causes the measurement errors to be large. In this study, hydrogen permeation properties through Nafion212 used as a standard PEM are evaluated using an in-situ measurement system in which both temperature and humidity are controlled at the same time.

• Journal of the Korean Electrochemical Society
• /
• v.7 no.4
• /
• pp.189-193
• /
• 2004

Lithium secondary battery with gel polymer electrolyte, which was composed of POAGA and TEGDMA, was prepared and its cell performances were evaluated. Collation time decreased with increasing the contents of the monomer in the POAGA-based gel polymer electrolyte. The polymer electrolyte was stable up to 4.5V electro-chemically and its ionic conductivity was $5.2\times10^{-3}Scm^{-1}$ at room temperature. The lithium-ion polymer battery with $3.0wt\%$ curable monomer and $1.0wt\%$ monomer showed rate-capability, low-temperature performance and cycleability.

• Journal of Electrochemical Science and Technology
• /
• v.2 no.4
• /
• pp.187-192
• /
• 2011

Photoelectrochemical performances of ZnO electrodes are enhanced by coupling with cobalt-based catalyst (CoPi) in phosphate electrolyte (pH 7). For this study, hexagonal pillar-shaped ZnO nanorods are grown on ZnO electrodes through a chemical bath deposition, onto which CoPi is deposited with different photodeposition times (10-30 min). A scanning electron microscopic study indicates that CoPi deposition does not induce any change of ZnO morphology and an energy-dispersive X-ray spectroscopic analysis shows that inorganic phosphate ions (Pi) exist on ZnO surface. Bare ZnO electrodes generate the current of ca. $0.36mA/cm^2$ at a bias potential of 0.5 V vs. SCE, whereas ZnO/CoPi (deposited for 10 min) has ca. 50%-enhanced current ($0.54mW/cm^2$) under irradiation of AM 1.5G-light ($400mW/cm^2$). The excess loading of CoPi on ZnO results in decrease of photocurrents as compared to bare ZnO likely due to limited electrolyte access to ZnO and/or CoPi-mediated recombination of photogenerated charge carriers. The primary role of CoPi is speculated to trap the photogenerated holes and thereby oxidize water into molecular oxygen via an intervalency cycle among Co(II), Co(III), and Co(IV).

• Journal of Hydrogen and New Energy
• /
• v.27 no.6
• /
• pp.677-684
• /
• 2016

Various commercially available gas diffusion layers (GDLs) from different manufacturers were used to prepare an air electrode using $La_{0.8}Sr_{0.2}CoO_3$ perovskite (LSCP) as the catalyst for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in an alkaline solution. Various GDLs have different physical properties, such as porosity, conductivity, hydrophobicity, etc. The ORR and OER of the resulting cathode were electrochemically evaluated in an alkaline solution. The electrochemical properties of the resulting cathodes were slightly different when compared to the physical properties of GDLs. Pore structure and conductivity of GDLs had a prominent effect and their hydrophobicities had a minor effect on the electrochemical performances of cathodes for ORR and OER.

• Journal of Hydrogen and New Energy
• /
• v.24 no.1
• /
• pp.61-69
• /
• 2013

Polymer exchange membrane (PEM) fuel cells have multifunctional properties, and bipolar plates are one of the key components in these fuel cells. Generally, a bipolar plate has a gas flow path for hydrogen and oxygen liberated at the anode and cathode, respectively. In this study, the influence of iodine applied to a bipolar plate was investigated. Accordingly, we compared bipolar plates with and without iodine coating, and the performances of these plates were evaluated under operating conditions of $75^{\circ}C$ and 100% relative humidity. The membrane and platinum-carbon layer were affected by the iodine-coated bipolar plate. Bipolar plates coated with iodine and a membrane-electrode assembly (MEA) were investigated by electron probe microanalyzer (EPMA) and energy-dispersive x-ray spectroscopy (EDS) analysis. Polarization curves showed that the performance of a coated bipolar plate is approximately 19% higher than that of a plate without coating. Moreover, electrochemical impedance spectroscopy (EIS) analysis revealed that charge transfer resistance and membrane resistance decreased with the influence of the iodine charge transfer complex for fuel cells on the performance.

• Resources Recycling
• /
• v.19 no.1
• /
• pp.27-32
• /
• 2010

To improve electronic conductivity of cathodic active materials of lithium ion battery, carbonaceous materials is usually added. New mixing method of abrasive milling has been investigated in mixing of graphite and $LiCoO_2$ powders. It would be expected that uniform mixing of graphite reduces capacity fading of cathode of lithium battery. Abrasion milled $LiCoO_2$ composite showed the best electrochemical performance as a cathode material with 1 wt% of graphite content, 300 rpm of milling speed, and 10 min of milling time. The improvement of the electrochemical performances such as cycleability and charge/discharge capacity retention would be mainly attributed to increase of the electronic conductivity and/or prevention of the active materials by uniform dispersion and coating of graphite on $LiCoO_2$.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2005.07a
• /
• pp.597-598
• /
• 2005

Recently, the performance of portable electric equipment can often improved by a Li-ion battery assisted by a supercapacitor. A supercapacitor can provide high power density as well as a low resistance in the hybrid system. In this study, we have prepared, as the pluse power souce, a commercially supplied Li-ion battery with a capacity of 700mAh and AC resistivity of $60m\Omega$ at 1kHz and nonaqeous asymmetric hybrid capacitor composed of an activated carbon cathode and MCMB anode, and have examined the electrochemical characteristics of hybrid capacitor and the pulse performances of parallel connected battery/hybrid capacitor source. The nonaqueous asymmetric hybrid capacitor, the stacks of 10 pairs of the cathode, the porous separator and the anode electrode were housed in Al-laminated film cell. The hybrid capacitor, which was charged and discharged at a constant current at $0.25mA/cm^2$ between 3 and 4.3V, has exhibited the capacitance of 100F. And the equivalent series resistance was $32m\Omega$ at 1kHz. By combining a Li-ion battery and a hybrid capacitor, the pulse performance of battery can be improved 23% in run time under a pulse discharge of 7C-rate.

• Journal of Powder Materials
• /
• v.26 no.3
• /
• pp.231-236
• /
• 2019

Ni hydroxides ($Ni(OH)_2$) are synthesized on Ni foam by varying the hexamethylenetetramine (HMT) concentration using an electrodeposition process for pseudocapacitor (PC) applications. In addition, the effects of HMT concentration on the $Ni(OH)_2$ structure and the electrochemical properties of the PCs are investigated. HMT is the source of amine-based $OH^-$ in the solution; thus, the growth rate and morphological structure of $Ni(OH)_2$ are influenced by HMT concentration. When $Ni(OH)_2$ is electrodeposited at a constant voltage mode of -0.85 V vs. Ag/AgCl, the cathodic current and the number of nucleations are significantly reduced with increasing concentration of HMT from 0 to 10 mM. Therefore, $Ni(OH)_2$ is sparsely formed on the Ni foam with increasing HMT concentration, showing a layered double-hydroxide structure. However, loosely packed $Ni(OH)_2$ grains that are spread on Ni foam maintain a much greater surface area for reaction and result in the effective utilization of the electrode material due to the steric hindrance effect. It is suggested that the $Ni(OH)_2$ electrodes with HMT concentration of 7.5 mM have the maximum specific capacitance (1023 F/g), which is attributed to the facile electrolyte penetration and fast proton exchange via optimized surface areas.

• Korean Journal of Metals and Materials
• /
• v.48 no.3
• /
• pp.262-267
• /
• 2010

$LiNi_{1-x}Mg_xO_2$(x=0, 0.025, 0.05, 0.075, 0.1) samples were synthesized by the solid-state reaction method. The crystal structure was analyzed by X-ray powder diffraction and Rietveld refinement. $LiNi_{1-x}Mg_xO_2$samples give single phases of hexagonal layered structures with a space group of R-3m. The calculated cation-anion distances and angles from the Rietveld refinement were changed with Mg contents in $LiNi_{1-x}Mg_xO_2$. The thicknesses of $NiO_2$ slabs were increased and the distances between the $NiO_2$ slabs were decreased with the increase in Mg contents in the samples. The electrical conductivities of sintered $LiNi_{1-x}Mg_xO_2$ samples were around $10^{-2}$ S/cm at room temperature. The electrochemical performances of $LiNi_{1-x}Mg_xO_2$were evaluated by coin cell test. Compared to $LiNiO_2$, $LiNi_{0.95}Mg_{0.05}O_2$ exhibited improved high-rate capability and cyclability due to the well-ordered layered structure by doping of Mg ion.