• 한국재료학회지
• /
• 제32권4호
• /
• pp.216-222
• /
• 2022

The capacity of high nickel Li(Ni_xCo_yMn_1-x-y)O₂ (NCM, x ≥ 0.8) cathodes is known to rapidly decline, a serious problem that needs to be solved in a timely manner. It was reported that cathode materials with the {010} plane exposed toward the outside, i.e., a radial structure, can provide facile Li⁺ diffusion paths and stress buffer during repeated cycles. In addition, cathodes with a core-shell composition gradient are of great interest. For example, a stable surface structure can be achieved using relatively low nickel content on the surface. In this study, precursors of the high-nickel NCM were synthesized by coprecipitation in ambient atmosphere. Then, a transition metal solution for coprecipitation was replaced with a low nickel content and the coprecipitation reaction proceeded for the desired time. The electrochemical analysis of the core-shell cathode showed a capacity retention of 94 % after 100 cycles, compared to the initial discharge capacity of 184.74 mA h/g. The rate capability test also confirmed that the core-shell cathode had enhanced kinetics during charging and discharging at 1 A/g.

• 한국분말재료학회지
• /
• 제30권2호
• /
• pp.107-115
• /
• 2023

Li_1.3Al_0.3Ti_1.7(PO₄)₃(LATP) is considered a promising material for all-solid-state lithium batteries owing to its high moisture stability, wide potential window (~6 V), and relatively high ion conductivity (10^-3-10^-4 S/cm). Solid electrolytes based on LATP are manufactured via sintering, using LATP powder as the starting material. The properties of the starting materials depend on the synthesis conditions, which affect the microstructure and ionic conductivity of the solid electrolytes. In this study, we synthesize the LATP powder using sol-gel and co-precipitation methods and characterize the physical properties of powder, such as size, shape, and crystallinity. In addition, we have prepared a disc-shaped LATP solid electrolyte using LATP powder as the starting material. In addition, X-ray diffraction, scanning electron microscopy, and electrochemical impedance spectroscopic measurements are conducted to analyze the grain size, microstructures, and ion conduction properties. These results indicate that the synthesis conditions of the powder are a crucial factor in creating microstructures and affecting the conduction properties of lithium ions in solid electrolytes.

• 한국재료학회지
• /
• 제22권3호
• /
• pp.118-122
• /
• 2012

We synthesized porous $Co_3O_4/RuO_2$ composite using the soft template method. Cetyl trimethyl ammonium bromide (CTAB) was used to make micell as a cation surfactant. The precipitation of cobalt ion and ruthenium ion for making porosity in particles was induced by $OH^-$ ion. The porous $Co_3O_4/RuO_2$ composite was completely synthesiszed after anealing until $250^{\circ}C$ at $3^{\circ}C$/min. From the XRD ananysis, we were able to determine that the porous $Co_3O_4$/RuO2 composite was comprised of nanoparticles with low crystallinity. The shape or structure of the porous $Co_3O_4/RuO_2$ composite was studied by FE-SEM and FE-TEM. The size of the porous $Co_3O_4/RuO_2$ composite was 20~40 nm. From the FE-TEM, we were able to determine that porous cavities were formed in the composite particles. The electrochemical performance of the porous $Co_3O_4/RuO_2$ composite was measured by CV and charge-discharge methods. The specific capacitances, determined through cyclic voltammetry (CV) measurement, were ~51, ~47, ~42, and ~33 F/g at 5, 10, 20, and 50 mV/sec scan rates, respectively. The specific capacitance through charge-discharge measurement was ~63 F/g in the range of 0.0~1.0 V cutoff voltage and 50 mAh/g current density.

• 한국전기전자재료학회논문지
• /
• 제27권9호
• /
• pp.582-588
• /
• 2014

3 mol% Co-added $Ni(OH)_2$ fine powders, which showed ${\beta}$-phase, as positive electrode materials have been fabricated using $NiSO_4{\cdot}6H_2O$ aqueous solution by ultrasonic spray-chemical precipitation and subsequent hydrothermal method, and sheet-like Ni nanopowder was fabricated by mechano-chemical reduction method. The addition effects of the sheet-like Ni nanopowder on the electrochemical properties of the positive electrode in Ni-Zn Redox flow battery were investigated. Impedance spectroscopy revealed that the addition of the sheet-like Ni nanopowder resulted in decrease in the electrical resistivity; 10 wt.% addition reduced the electrical properties by a fifth. Cyclic voltammetry showed the addition of the sheet-like Ni nanopowder resulted in decrease in the potential difference of oxidation and reduction; this means the increase in the reversability for electrode reduction. Charge/discharge measurement confirmed that the addition of the sheet-like Ni nanopowder resulted in the increase in the discharge efficiency.

• 한국재료학회지
• /
• 제21권8호
• /
• pp.419-424
• /
• 2011

Pt nanoparticle catalysts incorporated on $RuO_2$ nanowire support were successfully synthesized and their electrochemical properties, such as methanol electro-oxidation and electrochemically active surface (EAS) area, were demonstrated for direct methanol fuel cells (DMFCs). After fabricating $RuO_2$ nanowire support via an electrospinning method, two different types of incorporated Pt nanoparticle electrocatalysts were prepared using a precipitation method via the reaction with $NaBH_4$ as a reducing agent. One electrocatalyst was 20 wt% Pt/$RuO_2$, and the other was 40 wt% Pt/$RuO_2$. The structural and electrochemical properties of the Pt nanoparticle electrocatalysts incorporated on electrospun $RuO_2$ nanowire support were investigated using a bright field transmission electron microscopy (bright field TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and cyclic voltammetry. The bright field TEM, XRD, and XPS results indicate that Pt nanoparticle electrocatalysts with sizes of approximately 2-4 nm were well incorporated on the electrospun $RuO_2$ nanowire support with a diameter of approximately 50 nm. The cyclic voltammetry results showed that the Pt nanoparticle catalysts incorporated on the electrospun $RuO_2$ nanowire support give superior catalytic activity in the methanol electro-oxidation and a higher electrochemically active surface (EAS) area when compared with the electrospun Pt nanowire electrocatalysts without the $RuO_2$ nanowire support. Therefore, the Pt nanoparticle catalysts incorporated on the electrospun $RuO_2$ nanowire support could be a promising electrode for direct methanol fuel cells (DMFCs).

• Corrosion Science and Technology
• /
• 제2권3호
• /
• pp.117-126
• /
• 2003

Due to excellent corrosion resistance and mechanical properties, austenitic stainless steel is widely used as the material for chemical plants. nuclear power plants, and food processing facilities. But, the zone affected by heat in the range of 400 to $800^{\circ}C$ during welding loses corrosion resistance and tensile strength since Cr-carbide precipitation like $Cr_{23}C_6$ forms at the grain boundary and thereby takes place the intergranular corrosion. In this study, AISI 304 stainless steel with the added Nb of 0.3 to 0.7 wt% was solutionized at $1050^{\circ}C$ and sensitized at $650^{\circ}C$. Specimen was welded by MIG. The phase and the microstructure of the specimens were examined by an optical microscope, a scanning electron microscope, and a x-ray diffractometer. The corrosion characteristics of specimens were tested by electrolytic etching and by double loop electrochemical potentiokinetic reactivation method(EPR) in the mixed solution of 0.5M $H_2SO_4$ + 0.01M KSCN. The melting zone had dendritic structure constituted of austenitic phase and $\delta$-ferrite phase. Cr carbide at the matrix did not appear, as Nb content increased. At the grain boundaries of the heat affected zone, the precipitates decreased and the twins appeared. The hardness increased, as Nb content increased. The hardness was highest in the order of the heat affected zone>melted zone>matrix. According to EPR curve, as the Nb content decreased, the reactivation current density(Ir) and the activation current density(la) were highest in the order of the melted zone

• 한국재료학회지
• /
• 제20권12호
• /
• pp.669-675
• /
• 2010

One of the greatest challenges for our society is providing powerful electrochemical energy conversion and storage devices. Rechargeable lithium-ion batteries and fuel cells are among the most promising candidates in terms of energy and power density. As the starting material, $TiCl_4{\cdot}YCl_3$ solution and dispersing agent (HCP) were mixed and synthesized using ammonia as the precipitation agent, in order to prepare the nano size Y doped spherical $TiO_2$ precursor. Then, the $Li_4Ti_5O_{12}$ was synthesized using solid state reaction method through the stoichiometric mixture of Y doped spherical $TiO_2$ precursor and LiOH. The Ti mole increased the concentration of the spherical particle size due to the addition of HPC with a similar particle size distribution in a well in which $Li_4Ti_5O_{12}$ spherical particles could be obtained. The optimal synthesis conditions and the molar ratio of the Ti 0.05 mol reaction at $50^{\circ}C$ for 30 minutes and at $850^{\circ}C$ for 6 hours heat treatment time were optimized. $Li_4Ti_5O_{12}$ was prepared by the above conditions as a working electrode after generating the Coin cell; then, electrochemical properties were evaluated when the voltage range of 1.5V was flat, the initial capacity was 141 mAh/g, and cycle retention rate was 86%; also, redox reactions between 1.5 and 1.7V, which arose from the insertion and deintercalation of 0.005 mole of Y doping is not a case of doping because the C-rate characteristics were significantly better.

• 자원리싸이클링
• /
• 제29권1호
• /
• pp.25-34
• /
• 2020

전기화학적 미소수정진동자저울은 전극표면에서 발생하는 나노그램 수준의 질량변화를 실시간 측정할 수 있는 장비이다. 역압전효과를 가진 수정진동자 양면에 형성된 금속전극에 교대로 전계를 가하면 진동자의 두께에 따라 특정 공진주파수를 나타낸다. 공진주파수는 전극표면에서 발생하는 질량변화에 반응하며, 전극표면의 금속이 용해될 때는 증가하고 석출될 때는 반대로 감소한다. 공진주파수와 질량변화의 상관관계는 Sauerbrey 식으로 나타내고 이를 이용하여 금속의 침출반응때 발생하는 질량변화를 실시간으로 측정할 수 있다. 특히 용해 후 침출액에서 침전, 휘발, 기타 화합물 형성 등 부반응으로 실험 후 발광분광분석이나 원자흡광분석 등이 용이하지 않은 금속의 침출 반응기구 및 속도 연구에 매우 효과적이다. 그러나 수정진동자의 공진주파수는 질량변화 외에도 용액의 점도, 수압, 온도, 스트레스, 그리고 표면거칠기 등에도 영향을 받으므로 실험 시 이들 영향에 대한 고려가 필요하다. 전기화학적 미소수정진동자저울의 응용 예로서 염소를 이용한 백금의 침출 시 용해속도를 실시간 측정하고 이로부터 활성화에너지를 구하는 일련의 과정을 소개하였다. 침출에 사용된 백금시료는 수정진동자 양면에 형성된 1000 Å두께의 백금전극 중 침출액에 노출된 한쪽 면을 활용하였으며, 전해생성된 염소를 염산 침출액에 주입하여 침출 시 용존 염소농도를 조절하였다. 실험결과로부터 염소에 의한 백금의 용해반응은 활성화에너지가 83.5 kJ/mol로 화학반응율속임을 확인하였다.

• Korean Chemical Engineering Research
• /
• 제54권1호
• /
• pp.127-134
• /
• 2016

A series of Ce-doped ZnO (Ce/ZnO) nanostructures were fabricated using the co-precipitation method, then a simply nontoxic hydrothermal approach was proposed for preparation of reduced graphene oxide (rGO)-Ce/ZnO composites. The synthesized composites were investigated by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), photoluminescence spectroscopy (PL), electrochemical impedance spectroscopy (EIS), UV-vis diffuse reflectance spectroscopy (DRS) techniques and Raman pattern. The as-synthesized rGO-Ce/ZnO composites showed high photodecomposition efficiency in comparison with the rGO-ZnO, Ce/ZnO, pure ZnO under UV, visible-light and sunlight irradiation. The degradation of methylene blue (MB) (10 mg/L, 100ml) by 95.8% within 60 min by using rGO-2 (10 mg) under sunlight irradiation was observed. The repeated use of the rGO-2 was investigated, and the results showed almost no decay in the catalytic activity.

• 한국수소및신에너지학회논문집
• /
• 제6권2호
• /
• pp.65-73
• /
• 1995

Negative electrode was prepared by mixing $Ti_{0.7}Zr_{0.3}Cr_{0.3}Mn_{0.3}V_{0.6}Ni_{0.8}$ alloy powder with copper or nickel powder and pressing in the air. The cycled electrodes were analyzed with SEM, potentiostat and electrochemical impedance spectroscopy. It was found that the Cu-compacted electrode showed better low temperature dischargeability and higher rate capability than Ni-compacted electrode. From SEM analysis of the cycled electrode compacted with copper powder, it was observed that the surface of MH particles was covered with copper grains and whisker precipitated from electrolyte after dissolution during cell test. It is found that the improved electrode characteristics are attributed to the copper layer on MH particles deposited by dissolution and precipitation(DP) process.