• Bulletin of the Korean Chemical Society
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• v.32 no.6
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• pp.2045-2050
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• 2011

Using first principles density functional theory the formation energies of various binary compounds of lithium graphite and its homologues were calculated. Lithium and graphite react to form $Li_1C_6$ (+141 mV) but not form $LiC_4$ (-143 mV), $LiC_3$ (-247 mV) and $LiC_2$ (-529 mV) because they are less stable than lithium metal itself. Properties of structure and reaction potentials of $C_5B$, $C_5N$ and $B_3N_3$ materials as iso-structural graphite were studied. Boron and nitrogen substituted graphite and boron-nitrogen material as a iso-electronic structured graphitic material have longer graphene layer spacing than that of graphite. The layer spacing of $Li_xC_6$, $Li_xC_5B$, $Li_xC_5N$ materials increased until to x=1, and then decreased until to x=2 and 3. Nevertheless $Li_xB_3N_3$ has opposite tendency of layer spacing variation. Among various lithium compositions of $Li_xC_5B$, $Li_xC_5N$ and $Li_xB_3N_3$, reaction potentials of $Li_xC_5B$ (x=1-3) and $Li_xC_5$ (x=1) from total energy analyses have positive values against lithium deposition.

• Applied Chemistry for Engineering
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• v.16 no.1
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• pp.107-111
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• 2005

We have performed a study on the electrochemical characteristics and nuclear ($^7Li$) magnetic resonance of $V_2O_5$ xerogels that have been synthesized by the sol-gel reaction of $V_2O_5$ powder with hydrogen peroxide. NMR measurements revealed that chemical shift of $Li^+$ ions varied as lithium ions were inserted into $V_2O_5$ xerogel and that several different sites for $Li^+$ ions existed in the $V_2O_5$ xerogel structure. The electrochemical properties of the xerogel electrodes did not depend much upon the concentration of $V_2O_5$ and HCl that were used for the synthesis of $V_2O_5$ gels. The specific capacity of $V_2O_5$ xerogels were about 140 mAh/g, similar to that of the xerogels prepared by the ion exchange method.

• Bulletin of the Korean Chemical Society
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• v.28 no.12
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• pp.2226-2230
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• 2007

As a cathode material of lithium rechargeable batteries, charged Li[Co0.1Ni0.15Li0.2Mn0.55]O2 electrodes, which were aged thermally at 25 oC and 90 oC respectively, were characterized by means of charge/discharger, impedance spectroscopy, and X-ray diffraction. The discharge capacity diminution of the electrodes aged at 25 oC and 90 oC for 1 week was 4% and 23%, respectively. The cell aged at 25 oC was recovered on cycling. However, the capacity loss after ageing at 90 oC was not recovered in a subsequent cycling test, which demonstrates that the reaction occurring during ageing at 90 oC is irreversible. A significant impedance increase of aged electrode at 90 oC is associated with irreversible capacity loss. The structural changes including phase transformation were not detected by XRD analysis, because it could be due to out of detection limit. After ageing, impedance was slightly decreased during subsequent cycling test. It could be explained the cyclic performance of aged sample is stable. The thermal stability was not deteriorated by ageing even at the high temperature of 90 oC.

• Journal of the Korean Electrochemical Society
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• v.5 no.3
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• pp.159-163
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• 2002

The use of lithium metal anode at lithium metal secondary battery can provide the very high energy density. Nevertheless, there are some problems that are short cycle life, lack of safety and poor thermal stability. Cycle life and cycling efficiency decline due to passivating films, dendritic lithium and increasing surface film by the reaction of lithium metal and electrolyte. This work investigated the additive effect of benzene, toluene, tetram-ethylethylenediamine, into the electrolyte. The cycling efficiency and cyclability are improved. The reason is confirmed by decreasing film resistance and increasing polarization resistance at AC impedance analysis. Electrolyte additive has a relatively less reactivity than electrolytes lithium and is adsorbed on lithium leading to suppression of the reaction between the electrolyte and lithium as well as an improvement in the lithium deposition mophology.

• Journal of the Korean Electrochemical Society
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• v.2 no.2
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• pp.61-65
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• 1999

A new treatment of $LiV_3O_8$ has been proposed for improving its electrochemical behavior as a cathode material for secondary lithium batteries. Lithium trivanadate, $LiV_3O_8$, can be prepared in a finely dispersed form by dehydration of aqueous lithium trivanadate gels. The ultrasonic treatment method for Liv30s has been examined in comparison with $LiV_3O_8$ prepared by solutionmethod. The ultrasonically treated products in water were characterized by XRD (X-ray diffractometry), TGA (thermogravimetric analysis) and SEM (scanning electron microscopy). These measurements showed that the ultrasonic treatment process of aqueous $LiV_3O_8$ caused a decrease in crytallinity and considerable increased in specific surface area and interlayer spacing. The product, ultrasonically treated in water for 2 h, showed a high initial discharge capacity and was charge-discharge cycled without large capacity loss. The ultrasonic treated Liv30s can improve not only the specific capacity, but also the cycling behavior

• Journal of the Korean Electrochemical Society
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• v.11 no.4
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• pp.297-303
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• 2008

$LiNiO_2$ cathode powders with fine size have been synthesized by spray pyrolysis from the spray solution with citric acid and ethylene glycol. The as-prepared powders with spherical shape, porous structure and micron size turned into $LiNiO_2$ powders with micron size and regular morphology after post-treatment at $800^{\circ}C$. The initial discharge capacities of the $LiNiO_2$ powders changed from 199 to 171mAh/g when the concentrations of the citric acid and ethylene glycol added to the spray solutions were changed from 0 to 1 M. The maximum initial discharge capacity of the $LiNiO_2$ powders obtained from the spray solution with citric acid and ethylene glycol was 198 mAh/g when the lithium component added to the spray solution was 6 mol% excess of the stoichiometric amount. The discharge capacities of the fine-sized $LiNiO_2$ powders dropped from 198 to 163 mAh/g by the 30 th cycle at a current density of 0.1 C.

• Applied Chemistry for Engineering
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• v.19 no.6
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• pp.583-591
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• 2008

Recently, as a demand for the portable device is surged, there are needs to develop a new fuel cell system for replacing the conventionally used secondary battery. For this purpose, it becomes important to develop direct formic acid fuel cell (DFAFC) that uses formic acid as a fuel. The formic acid can offer typical advantages such as excellent non-toxicity of the level to be used as food additive, smaller crossover flux through electrolyte, and high reaction capability caused by high theoretical electromotive force (EMF). With the typical merits of formic acid, the efforts for optimizing reaction catalyst and cell design are being made to enhance performance and long term stability of DFAFC. As a result, to date, the DFAFC having the power density of more than $300mW/cm^2$ was developed. In this paper, basic performing theory and configuration of DFAFC are initially introduced and future opportunities of DFAFC including the development of catalyst for the anode electrode and electrolyte, and design for the optimization of cell structure are discussed.

• Journal of the Korean Electrochemical Society
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• v.14 no.3
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• pp.157-162
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• 2011

The stability at elevated temperatures of a surface film formed on a graphite electrode in lithium secondary batteries was investigated by transmission electron microscopy (TEM) and electrochemical AC impedance spectroscopy (EIS). TEM analysis revealed that the surface film partly dissolved in the electrolyte solution during storage at $60^{\circ}C$, resulting in a decrease in the thickness of the surface film and a change in its morphology to a porous structure. On the other hand, an increase in the impedance of the surface film which is attributable to a change in composition of the surface film was confirmed by EIS analysis during the storage at $60^{\circ}C$. It was also shown that the addition of vinylene carbonate or 1,3-propane sultone or etylene sulfite, even if limited, improves the stability of the surface film at elevated temperatures.

• Journal of the Korean Electrochemical Society
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• v.13 no.3
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• pp.186-192
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• 2010

In situ electrochemical atomic force microscopy (ECAFM) observations of the surface of highly oriented pyrolytic graphite (HOPG) was performed before and after cyclic voltammetry in lithium bis(fluorosulfonyl)imide (LiTFSI) dissolved in 1-buthyl-2,3-dimethylimidazolium (BDMI)-TFSI to understand the interfacial reactions between graphite and BDMI-based ionic liquids. The formation of blisters and the exfoliation of graphene layers by the intercalation of $BDMI^+$ cations within HOPG were observed instead of reversible lithium intercalation and de-intercalation. On the other hand, lithium ions are reversibly intercalated into the HOPG and de-intercalatied from the HOPG without intercalation of the $BDMI^+$ cations in the presence of 15 wt% of 4.90 mol/$kg^{-1}$ LiTFSI dissolved in propylene carbonate (PC). ECAFM results revealed that the concentrated PC-based solution is a very effective additive for preventing $BDMI^+$ intercalation through the formation of solid electrolyte interface (SEI).

• Bulletin of the Korean Chemical Society
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• v.34 no.10
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• pp.3033-3038
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• 2013

Nanoscale Chevrel $Mo_6S_8$ powders are synthesized by molten salt synthesis. Synthesized $Mo_6S_8$ powders have different mean particle sizes which are dependent on a ratio of salt to precursor. The particle sizes of $Mo_6S_8$ powders changes along with the ratio increase. $Mo_6S_8$ (6:1) demonstrates the best electrochemical characteristics among the synthesized $Mo_6S_8$ powders although the $Mo_6S_8$ (4:1) has the smallest particle size. $Mo_6S_8$ (6:1) shows a reversible capacity of 83.9 $mAhg^{-1}$, which is 27.5% and 33% improved value over $Mo_6S_8$ (2:1) and $Mo_6S_8$ (4:1) at a current density of 0.2C, respectively. The superior electrochemical properties of $Mo_6S_8$ (6:1) are attributed to the balanced particle size which provides proper contact area with electrolyte and the shortened $Mg^{2+}$ diffusion length. The $Mo_6S_8$ (4:1) has the smallest particle size but further reduction of particle size from $Mo_6S_8$ (6:1) is not advantageous.