• Proceedings of the Korean Fiber Society Conference
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• 1996.10a
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• pp.124-130
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• 1996

The hydrocarbons containing more than 10 carbons(0.1% of total volume, C10+), residue of aromatization from aliphatic hydrocarbons, were condensated in the presence of catalyst aluminumchloride and cocatalyst nitrobenzene(NB) to be pitchs with desirable properties. The properties of pitch were affected by the concentration of cocatalyst chosen 20 and 30wt.%. The pitch with 30wt.% NB showed higher carbon yield and lower crystallinity than that with 20wt.% NB. The two pitches were heat treated at 1000C and measured of charge/discharge capacity of the carbon as an anode. The carbon prepared at 20wt.% NB exhibited excellent cyclic stability with a capacity of 218mAh/.g and that at 30wt.% exhibited rather low cyclic stability with higher capacity of 235mAh/g.

• Journal of the Korean Ceramic Society
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• v.42 no.9 s.280
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• pp.602-606
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• 2005

[ $LiCoO_{2}$ ] is the most common cathode electrode materials in Lithium-ion batteries. $LiCo_{0.97}Mg_{0.03}O_2$ was synthesized by the solid-state reaction method. We investigated crystal structures, electrical conductivities and electrochemical properties. The crystal structure of $LiCo_{0.97}Mg_{0.03}O_2$ was analyzed by X-ray powder diffraction and Rietveld refinement. The material showed a single phase of a layered structure with the space group R-3m. The lattice parameter(a, c) of $LiCo_{0.97}Mg_{0.03}O_2$ was larger than that of $LiCoO_2$. The electrical conductivity of sintered samples was measured by the Van der Pauw method. The electrical conductivities of $LiCoO_2$ and $LiCo_{0.97}Mg_{0.03}O_2$ were $2.11{\times}10^{-4}\;S/cm$ and $2.41{\times}10^{-1}\;S/cm$ at room temperature, respectively. On the basis of the Hall effect analysis, the increase in electrical conductivities of $LiCo_{0.97}Mg_{0.03}O_2$ is believed due to the increased carrier concentrations, while the carrier mobility was almost invariant. The electrochemical performance was investigated by coin cell test. $LiCo_{0.97}Mg_{0.03}O_2$ showed improved cycling performance as compared with $LiCoO_2$.

• Proceedings of the Korea Crystallographic Association Conference
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• 2002.11a
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• pp.16-16
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• 2002

The presently commercialized lithium-ion batteries use layer structured LiCoO₂ cathodes. Because of the high cost and toxicity of cobalt, an intensive search for new cathode materials has been underway in recent years. Recently, a concept of a one-to-one solid state mixture of LiNO₂ and LiMnO₂, i.e., Li[Ni/sub 0.5/Mn/sub 0.5/]O₂, was adopted by Ohzuku and Makimura to overcome the disadvantage of LiNiO₂ and LiMnO₂. Li[Ni/sub 0.5/Mn/sub 0.5/]O₂ has the -NaFeO₂ structure, which is characteristic of the layered LiCoO₂ and LiNiO₂ structures and shows excellent cycleability with no indication of spinel formation during electrochemical cycling. Layered Li[Ni/sub x/Co/sub 1-2x/Mn/sub x/]O₂ (x = 0.5 and 0.475) materials with high homogeneity and crystallinity were synthesized using a mechanical alloying method. The Li[Ni/sub 0.475/Co/sub 0.05/Mn/sub 0.475/]O₂ electrode delivers a high discharge capacity of 187 mAh/g between 2.8 and 4.6 V at a high current density of 0.3 mA/㎠(30 mA/g) with excellent cycleability. The charge/discharge and differential capacity vs. voltage studies of the Li[Ni/sub x/Co/sub 1-2x/Mn/sub x/]O₂ (x = 0.5 and 0.475) materials showed only one redox peak up to 50 cycles, which indicates that structural phase transitions are not occurred during electrochemical cycling. The magnitude of the diffusion coefficients of lithium ions for Li[Ni/sub x/Co/sub 1-2x/Mn/sub x/]O₂(x = 0.5 and 0.475) are around 10/sup -9/ ㎠/s measured by the galvanostatic intermittent titration technique (GITT).

• Korean Journal of Materials Research
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• v.12 no.9
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• pp.712-717
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• 2002

New wet chemical method so called precipitation-evaporation method was suggested for preparing spinel structure lithium manganese oxide ($LiMn_2$$O_4$) for Li ion secondary battery. Using precipitation-evaporation method, $LiMn_2$$O_4$ cathode materials suitable for Li ion secondary batteries can be synthesized. Single spinel phase $LiMn_2$$O_4$ powder was synthesized at lower temperature compared to that of prepared by solid-state method. $LiMn_2$$O_4$ powder prepared by precipitation-evaporation method showed uniform, small size and well defined crystallinity particles. Li ion secondary battery using $LiMn_2$$O_4$ as cathode materials prepared by precipitation-evaporation method and calcined at $800^{\circ}C$ showed discharge capacity of 106.03mAh/g and discharge capacity of 95.60mAh/g at 10th cycle. Although Li ion secondary battery showed somewhat smaller initial capacity but good cyclic ability. It is suggested that electro-chemical properties can be improved by controlling particle characteristics by particle morphology modification during calcination and optimizing Li ion secondary battery assembly conditions.

• Journal of the Mineralogical Society of Korea
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• v.16 no.3
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• pp.223-232
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• 2003

The co-precipitation method is applied to synthesize the cathode material Li[L $i_{x}$M $n_{1-x-y}$C $r_{y}$ ] $O_2$ for lithium rechargeable batteries at $650^{\circ}C$ (CR650) and 8$50^{\circ}C$ (CR850), respectively. Rietveld indices indicate that $R_{wp}$ with respect to $R_{exp}$ ( $R_{wp}$/ $R_{exp}$) are 9.2%/10.1% for CR650 and 15.9%/9.76% for CR850, respectively. $R_{B}$ and S (GofF) shows 10.9%, 8.54% and 1.9, 1.6, respectively. Rietveld structure refinement reveals that layer structure of LiMn $O_2$ (R3m) coexists with lower symmetry of Li[L $i_{1}$3/M $n_{2}$3/] $O_2$ (C2/c) due to superlattice ordering of Li and Mn in metal-transition containing layers. Unit-cell parameters are calculated as a=2.8520(2)$\AA$, c=14.248(2)$\AA$, V=100.40(l)$\AA^3$ for CR650, and a=2.8504(1)$\AA$, c=14.2371(7)$\AA$, V=100.179(8)$\AA^3$ for CR850. Final chemistry is obtained as Li[L $i_{0.35}$M $n_{0.56}$C $r_{0.09}$] $O_2$ (CR650) and Li[L $i_{0.27}$M $n_{0.61}$C $r_{0.13}$] $O_2$ (CR850), respectively.y...y..vely.y...y..

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.8 no.4
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• pp.660-666
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• 1998

We discussed structure, energy state, characteristics of thermal stability, and electrochemical properties of Li-GFICs, Li-PCICs, and Li-AGICs during the intercalation process. According to X-ray diffraction patterns, we observed phase of stage 2 mainly from Li-GFICs, while stage 1 phase as well as stage 2 from Li-PCICs. For the structure of Li-AGICs, stage 1 phase was dominant, but it was not possible to obtain pure stage 1 compound probably due to structural characteristics of artificial graphite. We measured energy state of the compounds to stage stability, and revealed that Li-AGICs and Li-GFICs were in more stable state than Li-PCICs. Therefore, those two compounds could be excellent candidate for energy reserve material. From the study of thermal degradation, Li-GFICs showed strong exothermic reaction at around 300 and $400^{\circ}C$. In the study of thermal stability of Li-AGIC at various temperatures, we observed that lithium was not completely deintercalated and high stage was maintained even at high temperature. In the case of charge, discharge, and electrochemical studies, Li-GFICs showed the best results.

• Clean Technology
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• v.24 no.1
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• pp.77-84
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• 2018

In this study, $Li_4Ti_5O_{12}$ anode materials for lithium ion battery were synthesized by dry ball-mill method. Polyvinyl chloride (PVC) as a carbon source was added to improve electrochemical properties. When the PVC was added after $Li_4Ti_5O_{12}$ formation, the spinel structure was well synthesized and it was confirmed by X-ray diffraction (XRD) experiments. When the carbon material was added before the synthesis and the heat treatment was performed, it was confirmed that a material having a different crystal structure was synthesized even when a small amount of carbon material was added. In the case of $Li_4Ti_5O_{12}$ without the carbon material, the electrical conductivity value was about $10{\mu}S\;m^{-1}$, which was very small and similar to that of the nonconductor. As the carbon was added, the electrical conductivity was greatly improved and increased up to 10,000 times. Electrochemical impedance spectroscopy (EIS) analysis showed that the size of semicircle corresponding to the resistance decreased with the carbon addition. This indicates that the resistance inside the electrode is reduced. According to the Cyclic voltammetry (CV) analysis, the potential difference between the oxidation peak and the reduction peak was reduced with carbon addition. This means that the rate of lithium ion insertion and deinsertion was increased. $Li_4Ti_5O_{12}$ with 9.5 wt% PVC added sample showed the best properties in rate capabilities of $180mA\;h\;g^{-1}$ at 0.2 C-rate, $165mA\;h\;g^{-1}$ at 0.5 C-rate, and $95.8mA\;h\;g^{-1}$ at 5 C-rate.

• Journal of the Korean Ceramic Society
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• v.42 no.4
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• pp.292-297
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• 2005

$LiMO_{2}(M=Co,Ni)$ samples were synthesized with $Li_{2}CO_{3},\;Co_{3}O_{4}$, and NiO by the solid-state reaction method. In the case of $LiCoO_{2}$, at low temperature$(T=400^{\circ}C)$ spinel structure was synthesized and the obtained spinel phase was transformed to layered phase at high temperature$(T\ge600^{\circ}C)$. The phase transition behaviors of $LiCoO_{2}$ were investigated with various heating temperature and time. The rate of transition was directly proportional to the concentrations of reactant, and activation energy of reaction was around 6.76 kcal/mol. When CoO(rock salt structure) was used as a starting material instead of $Co_{3}O_{4}$(spinel structure), layered structure of $LiCoO_{2}$ was obtained at low temperature. In the case of $LiNiO_{2}$ the transition from layered structure to rock salt structure occurred easily by disordering/ordering reaction, but did not occur in $LiCoO_{2}$. The difference in metal ion radii in $LiCoO_{2}$ and $LiNiO_{2}$ results in different behaviors of phase transitions.

• Analytical Science and Technology
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• v.10 no.3
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• pp.209-215
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• 1997

Li-AGICs as a anode of secondary battery were synthesized by high-pressure method as a function of the Li-contents. The characteristics of these prepared compounds were determined from the studies with X-ray diffraction method, UV/VIS spectrophotometric and differential scanning calorimeter(DSC) analysis. From the results of X-ray diffraction, it was found that the lower stage intercalation compounds were formed with increase of Li-contents. The mixed stages in these compounds were also observed. In the case of the $Li_{30wt%}$-AGIC, the compounds in the stage 1 structure were formed predominantly, but the structure of only pure stage 1 for structural defect of artificial graphite is not observed. According to UV/VIS spectrophotometric analysis, $Li_{30wt%}$-AGIC shows distinguishable energy state spectrum with the position of $R(%)_{min}$ values, but the characteristic spectra of almost all Li-AGICs are not observed. The enthalpy and entropy changes of the compounds can be obtained from the differential scanning calorimetric analysis results. From the results, it was found that exothermic and endothermic reactions of Li-AGICs are related to thermal stability of lithium between artificial graphite layers.

• 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.