• Journal of the Korean Electrochemical Society
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• v.14 no.2
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• pp.117-124
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• 2011

We demonstrate a new surface modification of high-voltage lithium cobalt oxide ($LiCoO_2$) cathode active materials for lithium-ion batteries. This approach is based on exploitation of a polarity-tuned gel polymer electrolyte (GPE) coating. Herein, two contrast polymers having different polarity are chosen: polyimide (PI) synthesized from thermally curing 4-component (pyromellitic dianhydride/biphenyl dianhydride/phenylenediamine/oxydianiline) polyamic acid (as a polar GPE) and ethylene-vinyl acetate copolymer (EVA) containing 12 wt% vinyl acetate repeating unit (as a less polar GPE). The strong affinity of polyamic acid for $LiCoO_2$ allows the resulting PI coating layer to present a highly-continuous surface film of nanometer thickness. On the other hand, the less polar EVA coating layer is poorly deposited onto the $LiCoO_2$, resulting in a locally agglomerated morphology with relatively high thickness. Based on the characterization of GPE coating layers, their structural difference on the electrochemical performance and thermal stability of high-voltage (herein, 4.4 V) $LiCoO_2$ is thoroughly investigated. In comparison to the EVA coating layer, the PI coating layer is effective in preventing the direct exposure of $LiCoO_2$ to liquid electrolyte, which thus plays a viable role in improving the high-voltage cell performance and mitigating the interfacial exothermic reaction between the charged $LiCoO_2$ and liquid electrolytes.

• Proceedings of the Korean Radioactive Waste Society Conference
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• 2005.11a
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• pp.32-37
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• 2005

The characteristics of the metal melting and radionuclide distribution of the radioactive has been investigated in a lab-scale arc furnace. The slag former based on the constituents of silica, calcium oxide, aluminum oxide, borate and calcium fluoride additions was used for melting of the stainless and carbon steel. In the melting of the stainless steel, the amount of slag formation increased with an increase of the concentration of the slag former. But the effects of the slag basicity on the amount of stag formation showed a local maximum value of the slag formation with an increase of the basicity index in the melting of the stainless steel as well as in the melting of the carbon steel. With an increase of the amount of slag former addition, the trends of the cobalt distribution into the ingot and the stag depended on the kind of slag former used in the melting of the stainless steel while the effect of the slag basicity on the distribution of the cobalt was not clarified in the melting of carbon steel. Tn the melting of the carbon steel, the strontium was captured at up to $50\%$ into the slag phase. Cesium was completely eliminated from the melt of the stainless steel as well as the carbon steel and distributed to the dust phase.

• Journal of the Korean Electrochemical Society
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• v.11 no.4
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• pp.242-255
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• 2008

In lithium-ion batteries(LIB), the development of electrolytes had mainly focused on the characteristics of lithium cobalt oxide($LiCoO_2$) cathode and graphite anode materials since the commercialization in 1991. Various studies on compatibility between electrode and electrolytes had been actively developed on their interface. Since then, as they try to adopt silicon and tin as anode materials and three components(Ni, Mn, Co), spinel, olivine as cathode materials for advanced lithium batteries, conventional electrolyte materials are facing a lot of challenges. In particular, requirements for electrolytes performance become harsh and complicated as safety problems are seriously emphasized. In this report, we summarized the research trend of electrolyte materials for the electrode materials of lithium rechargeable batteries.

• Journal of Electrochemical Science and Technology
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• v.11 no.4
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• pp.352-360
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• 2020

Lithium cobalt oxide (LiCoO₂, LCO) has been widely used as a cathode material for Li-ion batteries (LIBs) owing to its excellent electrochemical performance and highly reproducible synthesis even with mass production. To improve the energy density of the LIBs for their deployment in electro-mobility, the full capacity and voltage of the cathode materials need to exploited, especially by operating them at a higher voltage. Herein, we doped LCO with divalent calcium-ion (Ca²⁺) to stabilize its layered structure during the batteries' operation. The Ca-doped LCO was synthesized by two different routes, namely solid-state and co-precipitation methods, which led to different average particle sizes and levels of dopant's homogeneity. Of these two, the solid-state synthesis resulted in smaller particles with a better homogeneity of the dopant, which led to better electrochemical performance, specifically when operated at a high voltage of 4.5 V. Electrochemical simulations based on a single particle model provided theoretical corroboration for the positive effects of the reduced particle size on the higher rate capability.

• Korean Journal of Materials Research
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• v.8 no.6
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• pp.484-492
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• 1998

The formation mechanism of the epitaxial cobalt silicide from Co/Ti/OOO) Si structure has been investigated. The transition temperature of CoSi to CoSi, was found to increase with increasing the Ti interlayer thickness, which may be owing to the occupation of the tetrahedral sites by Ti atoms in the CoSi crystal structure as well as the blocking effect of the Ti interlayer on the diffusion of Co. Also, the Co- Ti-O ternary compound formed at the metal! Si interface at the begining of silicidation, which seems to play an important role in epitaxial growth of Co silicide. The final layer structures obtained after a rapid thermal annealing of the Cot Ti/( 100) Si bi-layer structure turned out to be Ti oxide/Co- Ti-Si/epi-$CoSi_2$/OOO)

• Transactions of the Korean hydrogen and new energy society
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• v.20 no.6
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• pp.455-463
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• 2009

코발트 보호막 코팅이 적용된 페라이트계 스테인리스 스틸인 STS 430과 STS 444 소재에 대해 고체산화물 연료전지용 금속연결재로서의 고온 산화 특성에 대해 살펴보았다. 코발트 코팅층은 $800^{\circ}C$ 고온 산화 후 코발트 산화물 및 $Co_2CrO_4$, $CoCr_2O_4$, $CoCrFeO_4$ 등과 같은 코발트가 함유된 스피넬 상을 형성하였다. 또한 페라이트계 스테인리스 스틸과 코발트 코팅의 계면에서 크롬과 철이 함유된 치밀한 산화층을 형성하여 금속연결재 표면의 스케일 성장속도를 감소시키고 금속연결재 내에 함유된 크롬의 외부 확산을 효과적으로 억제하였다. 한편 STS 430은 고온 산화 후 표면에 형성된 스케일 하부에 $SiO_2$와 같은 내부 산화물이 형성된 반면 STS 444는 표면 스케일 이외에 다른 내부 산화물은 확인되지 않았으며 고온에서의 면저항 측정 결과, 코발트가 코팅된 STS 444의 전기 전도성이 STS 430 보다 우수한 것으로 나타났다.

• Journal of the Korean institute of surface engineering
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• v.56 no.1
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• pp.104-114
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• 2023

Three dimensional (3D) porous structures consisting of Cu@CoO core-shell-type nano-dendrites were synthesized and tested as the anode materials in lithium secondary batteries. For this purpose, first, the 3D porous films comprising Cu@Co core-shell-type nano-dendrites with various thicknesses were fabricated through the electrochemical co-deposition of Cu and Co. Then the Co shells were selectively anodized to form Co hydroxides, which was finally dehydrated to get Cu@CoO nanodendrites. The resulting electrodes exhibited very high reversible specific capacity almost 1.4~2.4 times the theoretical capacity of commercial graphite, and excellent capacity retention (~90%@50^th cycle) as compared with those of the existing transition metal oxides. From the analysis of the cumulative irreversible capacity and morphology change during charge/discharge cycling, it proved that the excellent capacity retention was attributed to the unique structural feature of our core-shell structure where only the thin CoO shell participates in the lithium storage. In addition, our electrodes showed a superb rate performance (70.5%@10.8 C-rate), most likely due to the open porous structure of 3D films, large surface area thanks to the dendritic structure, and fast electron transport through Cu core network.

• Journal of the Korean Chemical Society
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• v.57 no.6
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• pp.769-777
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• 2013

The effect of operating conditions (temperature and the partial pressures of H2 and CO) on the reaction rate of Fischer-Tropsch synthesis (FTS) were investigated by carrying out experiments according to a Box-Behnken design (BBD), and were mathematically modeled by using response surface methodology (RSM). The catalyst used was a nano-structured cobalt/manganese oxide catalyst, which was prepared by thermal decomposition. The rate of synthesis was measured in a fixed-bed micro reactor with $H_2/CO$ molar feed ratio of 0.32-3.11 and reactor pressure in the range of 3-9.33 bar at space velocity of $3600h^{-1}$ and a temperature range of 463.15-503.15 K, under differential conditions (CO conversion below 2%). The results indicated that in the present experimental setup, the temperature and the partial pressure of CO were the most significant variables affecting reaction rate. Based on statistical analysis the quadratic model of reaction rate of FTS was highly significant as p-value 0.0002.

• Korean Journal of Materials Research
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• v.24 no.1
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• pp.43-47
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• 2014

NiO-doped hibonite pigments were synthesized by the solid state method to get stabilized blue color pigment in both oxidation and reduction atmospheres. Optimum substitution condition with NiO for hibonite blue pigment was investigated. Experimental results were comparable to those of previous cobalt-minimization studies performed with other phosphate- or oxide-based cobalt-containing ceramic pigments (having olivine ($Co_2SiO_4$), spinel ($CoAl_2O_4$), or with co-doped willemite ($(Co,Zn)_2SiO_4$) structures). Composition was designed varying the NiO molar ratio increasing with $SnO_2$. The optimum substitution content is 0.93 mole NiO with 0.75mole $SnO_2$. The characteristics of the synthesized pigment were analyzed by XRD, Raman spectroscopy, SEM, and UV-vis. Synthesized pigment was applied to a lime-barium glaze with 10 wt% each and fired at an oxidation atmosphere of $1250^{\circ}C/1h$ and a reducing atmosphere $1240^{\circ}C/1h$. Blue color was obtained with $L^*a^*b^*$ values at 43.39, -6.78, -18.20 under a reducing atmosphere and 41.66, -6.36, -14.7 under and oxidation atmosphere, respectively.

• Journal of Technologic Dentistry
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• v.32 no.3
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• pp.195-207
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• 2010

Purpose: The purpose of this study was to observe the microstructural changes of surface in the specimens, performing the shear bond strength testing. The currently most used non-precious alloys are nickel-chromium based alloys with or without beryllium. However, their biocompatibility has been questioned concerning possible damages to the health of the patient and professionals involved in the fabrication of prosthesis caused by long exposure to Ni and Be. An option to nickel-chromium alloys is the cobalt-chromium alloy, an alternative that does not sacrifice the physical properties of the metal porcelain systems. Studies in the animals substantially show that the cobalt-chromium alloys are relatively well tolerated, being therefore more biocompatible than the nickel-chromium alloys. Methods: Non-addition Be to nickel-chromium based alloy(Bellabond plus) and cobalt-chromium alloy which has been widely used(Wirobond C) fused with ZEO light porcelain classified control group and cobalt-chromium alloy which is developing alloy of Alphadent company in Korea(Alphadent alloy) fused with ZEO light porcelain classified experimental group. The specimens of $4mm{\times}4mm{\times}0.5mm$ were prepared as-cast and as-opaque to cast body to analyze the mechanical characteristic change, the microstructure of alloy surface. The phase change was used to observe through XRD analysis and OM/SEM was used to observe the surface of specimens as-cast and as-opaque to cast body. Chemical formation of their elements was measured with EDS. Then hardness was measured with Micro Vicker's hardness tester. Shear bond strength test thirty specimens of $10mm{\times}10mm{\times}2mm$ was prepared, veneered, 3mm high and 3mm in diameter, over the alloy specimens. The shear bond strength test was performed in a universal testing machine(UTM) with a cross head speed of 0.5mm/min. Ultimate shear bond strength data were analyzed with one-way ANOVA and the Scheffe's test (P<0.05). Within the limits of this study, the following conclusions were drawn: The X-ray diffraction analysis results for the as-cast and as-opaque specimens showed that the major relative intensity of Bellabond plus alloy were changed smaller than Wirobond C and Alphadent Co-Cr based alloys. Results: Microstructural analysis results for the opaque specimens showed all the alloys increased carbides and precipitation(PPT). Alphadent Co-Cr based alloy showed the carbides of lamellar type. The Vickers hardness results for the opaque specimens showed Wirobond C and Alphadent Co-Cr based alloys were increaser than before ascast, but Bellabond plus alloy relatively decreased. The mean shear bond strengths (MPa) were: 33.11 for Wirobond C/ZEO light; 25.00 for Alphadent Co-Cr alloy/ZEO light; 18.02 for Bellabond plus/ZEO light. Conclusion: The mean shear bond strengths for Co-Cr and Ni-Cr based alloy were significantly different. But the all groups showed metal-metal oxide modes in shear bond strengths test at the interface.