• Journal of the Korean Electrochemical Society
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• v.6 no.1
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• pp.1-5
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• 2003

[ $LiNi_{1-x}Co_xO_2\;(x=0.0\~1.0)$ ] powders were synthesized by citrate method, and their crystal structures and electrochemical performance as the cathode material in Li secondary batteries were analyzed. X-ray diffraction analysis revealed that all the samples carry a single phase regardless of the Co substitution. The results of Rietveld refinement suggested that the crystal structure of solid solutions varies according to the Co substitution. When the Co substitution is low $(x=0.3\~0.5)$, the solid solutions carry a cubic-like structure with a relatively small value in the ratio of lattice parameters (c/a). The solid solutions made with a higher Co substitution (x=0.7), however, exhibit a layered structure with a higher c/a ratio. This difference was also observed in the electrochemical voltage spectroscopy (EVS) profiles, whereby the Co component in scarcely substituted materials shows a charging reaction at $3.7V\;(vs.\;Li/Li^+)$, but in the heavily substituted ones at 3.92V.

• Journal of the Korean Electrochemical Society
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• v.17 no.3
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• pp.149-155
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• 2014

In this study, a positive-electrode material in a lithium secondary battery $Li[Ni_{0.575}Co_{0.1}Mn_{0.325}]O_2$ was synthesized as precursor by co-precipitation. Cathode material was synthesized by adding iron. The synthesized cathode material was analyzed by scanning electron microscope and x-ray diffraction. The analysis of x-ray diffraction showed that the a-axis and c-axis is increased by doping iron. And $I_{(003)}/I_{(104)}$ is increased and $I_{(006)}+I_{(102)}/I_{(101)}$ is decreased. Through this result, it was confirmed that the structural stability is improved. And impedance measurements show that the charge transfer resistance ($R_{ct}$) is lowered by doping iron. Consequently, electrochemical properties are improved by doping iron. In particular, the cycle characteristics are improved at a high temperature condition (328 K). Structural stabilities are contributing to the cycle properties.

• Journal of the Korean Electrochemical Society
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• v.20 no.2
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• pp.34-40
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• 2017

Electric double layer capacitors (EDLC: electric double layer capacitors) have drew attention as an energy storage device for the next generation because of their outstanding power capability and durability. But their usage is somewhat limited due to low energy density over secondary batteries. One of methods to improve the energy of EDLC is expanding the voltage window of cell operation by increasing the charge cut-off voltage. In this study, $SBP-BF_4$ (spirobipyrrolidinium tetrafluoroborate), $TEA-BF_4$ (tetraethylammonium tetraflouroborate) and $EMI-BF_4$ (1-ethyl-3-methylimidazolium tetrafluoroborate) in AN (acetonitrile) were selected to evaluate the possibility of application at high voltage environment. The LSV (linear sweep voltammetry) measurements showed that the 1.5M SBP-BF4/AN electrolyte was stable over a wide potential window and showed the best electrochemical performance compared to other combinations of electrolytes at high voltage environments (over 3.0 V). Furthermore, TMSP (tris(trimethylsilyl) phosphite) was applied to 1.5M SBP-BF4/AN in order to maintain stable performance at high voltage for the long period of time. The electrolyte with TMSP additive showed the capacity retention of 93% after 10,000 cycles at 3.3 V.

• Journal of the Korean Electrochemical Society
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• v.6 no.1
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• pp.6-12
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• 2003

Plasma carbon black(PB) which prepared by plasma pyrolysis of methane was treated at 800, 1300 and $2100^{\circ}C$ under $2\times10^{-2}$ torr. Four different samples including raw PB were added to $LiCoO_2$, cathode active material of lithium secondary battery, to investigate effects of properties of plasma black as conductors on electrochemical characteristics. Based on our experimental results, PB conductors with low amount of surface functional groups and high electrical conductivity enhanced the cyclability and the initial discharge capacity. However, deterioration of rate capability and cyclability were observed (or the plasma black treated at $2100^{\circ}C$ For the plasma black conductor prepared from plasma pyrolysis, the effects of properties of carbon black on electrochemical characteristics were combined results of changes in electrical conductivity and structural properties such as agglomeration of plasma black. The conductivity of plasma black increased with treatment temperature, while dispersion of plasma black decreased. As a result, the high cyclability of cell was observed at $800^{\circ}C$ of heat treatment temperature.

• Korean Chemical Engineering Research
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• v.58 no.1
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• pp.142-149
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• 2020

In this study, the electrochemical performance of Graphite/Silicon/Pitch composites as anode material was investigated to improve the low theoretical capacity of artificial graphite. Spherical artificial graphite surface was coated with polyvinylpyrrolidone (PVP) amphiphiles material to synthesize Graphite/Silica material by silica islands growth. The Graphite/Silicon/Pitch composites were prepared by petroleum pitch coating and magnesiothermic reduction. The Graphite/Silicon/Pitch composite electrodes manufactured using poly(vinylidene fluoride) (PVDF), carboxymethyl cellulose (CMC) and polyacrylic acid (PAA) binders. The coin type half cell was assembled using various electrolytes and additives. The Graphite/Silicon/Pitch composites were analysed by X-ray diffraction (XRD), scanning electron microscope (SEM) and a thermogravimetric analyzer (TGA). The electrochemical characteristics of Graphite/Silicon/Pitch composite were investigated by constant current charge/discharge, rate performance, cyclic voltammetry and electrochemical impedance spectroscopy. The Graphite/Silicon/Pitch composites showed high cycle stability at a graphite/silica/pitch ratio (1:4:8 wt%). When the electrode is prepared using PAA binder, the high capacity and stability is obtained. The coin type half cell assembled using EC: DMC: EMC electrolyte showed high initial capacity (719 mAh/g) and excellent cycle stability. The rate performance has an capacity retention (77%) at 2 C/0.1 C and an capacity recovery (88%) at 0.1 C / 0.1 C when the vinylene carbonate (VC) was added.

• Clean Technology
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• v.22 no.4
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• pp.308-315
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• 2016

$SiO_x/ZnO$ composites were prepared from sol-gel method for excellent cycle life characteristics. The composites were coated by PVC as a carbon precursor. ZnO removal to create a void space therein was able to buffer the volume change during charge and discharge. To determine the crystal structure and the shape of the synthesized composite, XRD, SEM, TEM analysis was performed. The carbon contents in the composites were confirmed by TGA. The pore structure and pore size distribution of the composite was measured with the BET specific surface area analysis and BJH pore size distribution. Enhanced electric conductivity by carbon addition was determined from powder resistance measurement. Electrochemical properties were measured with the AC impedance and the charge and discharge cycle life characteristics. When carbon was coated on the $SiO_x/ZnO$ sample, the electrical conductivity and the discharge capacity were increased. After removal of ZnO with HCl the surface area of the sample was increased, but the discharge capacity was decreased. $SiO_x/ZnO$ sample without acarbon coating showed very low discharge capacity, and after carbon coating the sample showed high discharge capacity. For cycle life characteristics, $C-SiO_x/ZnO$ composite (Zn : Si : C = 1 : 1 : 8) with a capacity of $815mAh\;g^{-1}$ at 50 cycle and 0.2 C has higher capacity than existing graphite-based anode materials.

• Applied Chemistry for Engineering
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• v.34 no.5
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• pp.529-533
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• 2023

The fundamental electrochemical properties and adsorption capabilities of the carbonized product derived from coffee grounds, a prevalent form of lignocellulose abundantly generated in our daily lives, have been extensively investigated. The structure and morphology of the resultant carbonized product, obtained through a carbonization process conducted at a relatively low temperature of 600 ℃, were meticulously examined using a scanning electron microscope. Raman spectroscopy measurements yielded a relative crystallinity (D/G ratio) of the carbon product of 0.64. Electrical measurements revealed a linear ohmic relationship within the carbonized product. Furthermore, the viability of utilizing this carbonized material as an anode in lithium-ion batteries was evaluated through half-cell charge/discharge experiments, demonstrating an initial specific capacity of 520 mAh/g. Additionally, the adsorption performance of the carbon material towards a representative dye molecule was assessed via UV spectroscopy analyses. Supplementary experiments corroborated the material's ability to adsorb a distinct model molecule characterized by differing surface polarity, achieved through surface modification. This article presents pivotal findings that hold substantial implications for forthcoming research endeavors centered around the recycling of lignocellulose waste.

• Journal of the Korean Electrochemical Society
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• v.19 no.3
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• pp.80-86
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• 2016

High Ni content layered oxide materials for the positive electrode in lithium-ion batteries have high specific capacity. However, their poor electrochemical and thermal stability at elevated temperature restrict the practical use. A small amount of $Al_2O_3$ was added to the mixture of transition metal hydroxide and lithium hydroxide. The $LiNi_{0.6}Co_{0.2}Mn_{0.2}O_2$ was simultaneously doped and coated with $Al_2O_3$ during heat-treatment. Electrochemical characteristics of modified $LiNi_{0.6}Co_{0.2}Mn_{0.2}O_2$ were evaluated by the galvanostatic cycling and the LSTA(linear sweep thermmametry) at the constant voltage conditions. The nano-sized $Al_2O_3$ added materials show better cycle performance at elevated temperature than that of micro-sized $Al_2O_3$. As the added amount of nano-$Al_2O_3$ increased, the thermal stability of electrode also enhanced, but the use of 2.5 mol% Al showed the best high temperature performance.

• Journal of the Korean Electrochemical Society
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• v.11 no.2
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• pp.120-124
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• 2008

Carbon-coated $LiFePO_4$ and $LiMn_{0.4}Fe_{0.6}PO_4$ cathode materials for lithium batteries were synthesized by a sol-gel method. X-ray diffraction and scanning electron microscopy data showed that the cathode materials are pure crystalline and are surrounded by porous carbon. The initial discharge capacities of $LiFePO_4$ and $LiMn_{0.4}Fe_{0.6}PO_4$ with the liquid electrolyte of 1M $LiPF_6$ in EC/DMC are 132 mAh/g and 145 mAh/g, respectively, at current density of 0.1 C-rate. $LiFePO_4$ and $LiMn_{0.4}Fe_{0.6}PO_4$ with an electrospun polymer-based electrolyte exhibit initial discharge capacities of 114 and 130 mAh/g at 0.1 C-rate at room temperature, respectively.

• Korean Journal of Materials Research
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• v.9 no.1
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• pp.14-17
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• 1999

Tin oxide films as an anode layer for microbatteries were deposited by using rf magnetron sputtering. Characterization of the films was carried out in terms of working pressure in the range of 5~30 mtorr. Rf power and substrate temperature during deposition were fixed at 2.5W/$\textrm{cm}^2$ and A.T., respectively. The crystal orientation of $SnO_2$films was changed from (110) to (101) or (211) with the increasing working pressure. Refractive index and film density of the films also decreased with the increasing working pressure. The $SnO_2$ thin film formed under optimum conditions was found to have a reversible capacity of 446.9$\mu$Ah/$\textrm{cm}^2$-$\mu\textrm{m}$ and good reversibility when the working pressure was fixed at 10mtorr. As the working pressure decreased, film density increased. It was thought that the capacity of $SnO_2$films increased due to the increase in the amount of active materials which can react with Li electrochemically. Furthermore, cycle characteristics of the anode material was also influenced by film stress.