• Journal of Electrochemical Science and Technology
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• 제13권2호
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• pp.269-278
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• 2022

Utilization of high-voltage electrolyte additive(s) at a small fraction is a cost-effective strategy for a good solid electrolyte interphase (SEI) formation and performance improvement of a lithium-rich layered oxide-based high-energy lithium-ion cell by avoiding the occurrence of metal-dissolution that is one of the failure modes. To mitigate metal-dissolution, we explored fluorinated dual-additives of fluoroethylene carbonate (FEC) and di(2,2,2-trifluoroethyl)carbonate (DFDEC) for building-up of a good SEI in a 4.7 V full-cell that consists of high-capacity silicon-graphite composite (15 wt% Si/C/CF/C-graphite) anode and Li_1.13Mn_0.463Ni_0.203Co_0.203O₂ (LMNC) cathode. The full-cell including optimum fractions of dual-additives shows increased capacity to 228 mAhg^-1 at 0.2C and improved performance from the one in the base electrolyte. Surface analysis results find that the SEI stabilization of LMNC cathode induced by dual-additives leads to a suppression of soluble Mn²⁺-O formation at cathode surface, mitigating metal-dissolution event and crack formation as well as structural degradation. The SEI and structure of Si/C/CF/C-graphite anode is also stabilized by the effects of dual-additives, contributing to performance improvement. The data give insight into a basic understanding of cathode-electrolyte and anode-electrolyte interfacial processes and cathode-anode interaction that are critical factors affecting full-cell performance.

• 대한금속재료학회지
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• 제49권7호
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• pp.530-534
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• 2011

To analyze the effect of the pore size of graphite in a pore-forming agent, graphite was added to porous ceramics of $Al_2O_3-SiO_2-ZrO_2$ systems. The graphite had 45~75, 100~125, 150~180, and 75~180${\mu}m$ dimensions. The properties of the ceramics, such as apparent porosity, density, dynamic elastic modulus, mechanical strength, and permeability, were investigated. The average pore size increased from 15.35${\mu}m$ to 22.32${\mu}m$ with the increase of the graphite size. The sample with the largest average pore size showed the highest mechanical strength and gas permeability. This was due to the sample with the largest pore size at the same porosity having fewer pores and larger distance between the pores than the sample with the smallest pore size, making cracks less likely to propagate. In addition, the large pore size reduced the repulsive power originating from the drag force between the gas and internal pore walls.

• 대한전자공학회논문지
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• 제27권4호
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• pp.527-533
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• 1990

Zone-melting recrystallization (ZMR) system using two graphite heaters(a stationary sheet and a narrow movable bar) was constructed and implemented in recrystallization op Si films on insulating layers. The recystallized Si films were examined by Nomarski contrast optical microscopy after Dash etching, transmission electron diffraction pattern, and x-ray diffraction. With optimum conditions of process parameters(input powers of the bottom and upper heater, scanning speed of the upper heater, and the gap between sample and upper heater), the recrystallized Si layer has a (100) texture, but contains many subboundaries. The subgrains are misoriented by < 0.5\ulcorner and the average spacing between subboundaries is about 25\ulcorner.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2007년도 추계학술대회 논문집
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• pp.43-44
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• 2007

SiO and graphite composite has been prepared by adopting high energy ball milling technique. The anode material shows high initial discharge and charge capacity values of 1138 and 568 mAh/g, respectively. Since the materials formed during initial discharge process the nano silicon/$Li_4SiO_3\;and\;Li_2O$ remains as interdependent, it may be expected that the composite exhibiting higher amount of irreversible capacity$(Li_2O)$ will deliver higher reversible capacity. In this study, pretreatment method of constant current-constant voltage (CC-CV) Provided high coulombic efficiency of SiO/C composite electrode removing the greater part of irreversible capacity.

• Journal of Electrochemical Science and Technology
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• 제2권3호
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• pp.146-151
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• 2011

The formation of Li-Si-O phases, $Li_4SiO_4$ and $Li_2SiO_3$ from the starting materials SiO and $Li_2O$ are analyzed using Vienna Ab-initio Simulation (VASP) package and the total energies of Li-Si-O compounds are evaluated using Projector Augmented Wave (PAW) method and correlated the structural characteristics of the binary system SiO-$Li_2O$ with experimental data from electrochemical method. Despite $Li_2SiO_3$ becomes stable phase by virtue of lowest formation energy calculated through VASP, the experimental method shows presence of $Li_4SiO_4$ as the only product formed when SiO and $Li_2O$ reacts during slow heating to reach $550^{\circ}C$ and found no evidence for the formation of $Li_2SiO_3$. Also, higher density of $Li_4SiO_4$(2.42 g $ml^{-1}$) compared to the compositional mixture $1SiO_2-2Li_2O$ (2.226 g $ml^{-1}$) and better cycle capacity observed through experiment proves that $Li_4SiO_4$ as the most stable anode supported by better cycleabilityfor lithium ion battery remains as paradox from the point of view of VASP calculations.

• 한국세라믹학회지
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• 제22권5호
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• pp.35-42
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• 1985

$eta$-Sialon powders were prepared by reduction-nitridation from mixture of Wando pyrophyllite and graphite as a reducing agent at 135$0^{\circ}C$ in 80% $N_2$-20% $H_2$ atmosphere. As the reaction products $Si_2ON_2$, $\beta$-$Si_3N_4$ a--$Si_3N_4$ and $\beta$-SiC were observed. Additive agents of MgO, CaO, $Y_2O_3$ were used for promoting the reduction and nitridiation aeaction. The present study was conducted to investigate the effects of silica-carbon ratio ($SiO_2$/C=weight ratio), raction time gas flow rate pellet size and powder packing on synthesis of $\beta$-Sialon from Wando pyropyllite.

• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2018년도 춘계학술대회 논문집
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• pp.71-71
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• 2018

현재 상용화된 Graphite 음극활물질의 경우 낮은 부피당, 무게당 용량을 가지며 이는 다양한 분야에 활용하는데 제약이 있다. $SiO_2$는 Si에 비해서는 낮은 용량이지만 metal oxide 계열 중 가장 높은 이론용량을 가지고 있으며, 리튬 이온과 반응 시 큰 부피팽창을 하며, 절연체로 전기전도도가 낮아 리튬이 차전지의 음극재로 상용화가 어려운 단점이 있다. 본 연구에서는 TEOS를 이용하여 탄소와 $SiO_2$를 동시에 $TiO_2$ microcone 구조에 코팅하여 3가지 물질의 복합체를 형성하여 용량을 증대시키고 구조적 안전성을 향상시키는 방법을 소개 한다. 음극재의 특성은 고분해능 주사전자현미경 (HR-SEM), 고분해능 엑스선 회절분석기 (XRD), 를 통해 조사하였으며, 순환전류법 (CV), 충 방전 싸이클 분석을 통해 리튬이차전지의 작동원리와 보다 향상된 성능을 규명하였다.

• 한국세라믹학회지
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• 제21권1호
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• pp.5-10
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• 1984

$eta$-Sialon synthesis was investigated via the simulataneous reduction and nitriding of Wando pyrophyllite. When Wando pyrophyllite-graphite-$Si_3N_4$ seed mixture was heated at 135$0^{\circ}C$ for as long as 10 hours in 80% $N_2$-20%$H_2$ atomsphere $eta$-$Si_3N_4$ solid solution was mainly formed together with a small amount of $\alpha$-$Si_3N_4$ The value z of the forming $Si_{6-x}Al_2O_2N{8-z}$ was decreased with heating time.

• Journal of Ceramic Processing Research
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• 제19권6호
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• pp.483-491
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• 2018

Effects of additives on phase development and physico-mechanical properties of mullite-carbon was investigated. Powdered clay, kaolinite and graphite of predetermined compositions were blended with additives using ball mill for 3 hrs at 60 rev/min. Samples were produced by uniaxial compression and sintered between $1400^{\circ}C$ and $1600^{\circ}C$ for one hr. They were characterized for various properties, developed phases and microstructural features. It was observed that the properties and phase developments in the samples were influenced by the additives. 10 wt % SiC served as nucleating point for SiC around $1400^{\circ}C$. 10wt % $TiO_2$ lead to development of 2.5 wt % TiC at $1500^{\circ}C$ which increased to 6.8 wt % at $1600^{\circ}C$. Ifon clay in the sample leads to development of anorthite and microcline in the samples. 10wt % $TiO_2$ is effective as anti-oxidant for graphite up to $1500^{\circ}C$. Base on strength and absorbed energy, sample C (with 10wt % $TiO_2$) sintered at $1500^{\circ}C$ is considered to be optimum.

• 한국세라믹학회지
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• 제24권2호
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• pp.139-146
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• 1987

${\beta}$-SiC powders were prepared by the simultaneous reduction and carbiding of Jecheon quartzite at 1400$^{\circ}C$ for 7 hours in hydrogen atmosphere, using graphite or carbon black as the reducing and carbiding reagent. The prepared SiC powder was acid-treated with the mixture of fluoric acid and hydrochloric acid at room temperature and also by heating on an alcohol lamp for one hour, respectively. The impurities were mostly eliminated and the purity of SiC became 98.5% after hot acid treatment. The specific surface area of SiC powder was also increased up to 115㎡/g by hot acid treatment. This pure and fine SiC powder was hot-pressed at 1900$^{\circ}C$ for 30min, using 5wt% Al2O3 as a sintering aid. The density, M.O.R., KIC and hardness of the hot-pressed SiC ceramics were 3.195g/㎤, 48.7Kgf/$\textrm{mm}^2$, 5.4MN/㎥/2 and 2,182Kgf/$\textrm{mm}^2$, respectively.