• Journal of the Korean Electrochemical Society
• /
• v.21 no.2
• /
• pp.39-46
• /
• 2018

Many studies on the electrochemical performance of Li secondary batteries have been obtained using coin-type cells due to the ease of assembly, low cost and ensuring reproducibility. The coin-type cell consists of a case, a gasket, a spacer disk, and a wave spring. These structural features require a greater amount of liquid electrolyte to assemble than other types of cells such as laminated cells and cylindrical cells. Nevertheless, little research has been conducted on the effect of excess liquid electrolytes on the electrochemical performances of Li secondary batteries. In this study, we investigate the effect of different amounts of electrolyte on the coin-type cells. The amount of electrolytes is adjusted to 30 and $100mg\;mAh^{-1}$. Cycle performances at room temperature ($25^{\circ}C$) and high temperature ($60^{\circ}C$) and high voltage are performed to investigate the electrochemical properties of the different amount of electrolytes. In the case of the unit cell including the electrolyte of $30mg\;mAh^{-1}$, the discharging capacity retention characteristic is excellent in comparison with the case of $100mg\;mAh^{-1}$ under the high temperature and high voltage condition. The former shows a larger increase in internal resistance than the latter, confirming that the amount of electrolyte significantly influences the discharge capacity retention characteristics of the battery.

• Journal of the Korean Electrochemical Society
• /
• v.2 no.2
• /
• pp.75-80
• /
• 1999

Li-ion cells employ lithium transtion metal oxide as the cathode material and carbon as anode material. To manufacture Li-ion cell with higher capacity and better cycle life, the utilization of electrode materials should be as high as possible without lithium deposition onto the carbon surface during charging. A careful design of cell balance between cathode and anode materials as well as a proper charge method is a key factor to design Li-ion cell with long cycle life. In this study, we investigated the effect of cathode/anode weight ratio on the performance of $LiCoO_2/MPCF$ cell. First we evaluated the charge-discharge behaviours of half-cells. And cylindrical Li-ion cells were fabricated using graphitized MPCF anode and $LiCoO_2$ cathode. The voltage profiles for each half-cell in $LiCoO_2/MPCF$ cell were measured by using lithium metal as a reference electrode. Also, we evaluated the cyclic performance of $LiCoO_2/MPCF$ cells according to weight ratio. From the result of experiment $LiCoO_2$ cathode utilization was independent of weight ratio, but MPCF anode utilization was dependant on weight ratio. Also, the optimal weight ratio of $LiCoO_2/MPCF$ cell was found to be $2.0\~2.2$.

• Korean Chemical Engineering Research
• /
• v.61 no.3
• /
• pp.362-367
• /
• 2023

Recently, research and development of proton exchange membrane fuel cells (PEMFC) membranes are progressing in the direction of thinning to reduce prices and improve performance. Demand for hydrogen-powered vehicles for commercial vehicles is also increasing, and their durability should be five times greater than those for passenger vehicles. Despite the thinning of the membranes, the durability of the membranes must be increased five times, so the improvement of the durability of the membranes has become more important. Since the acceleration durability evaluation time also needs to be shortened, the protocol using oxygen instead of air in the existing protocol was applied to a 10 ㎛ thin membrane to evaluate durability. The accelerated durability test (Open circuit voltage holding) was terminated at 720 hours. If the air-based department of energy (DOE) protocol was used, a lifespan of 450,000 km of driving hours would be expected, with a durability of about 1,500 hours. During the chemical durability evaluation, the active area of the electrode decreased by 51%, suggesting that catalyst degradation had an effect on membrane durability. Reducing the catalyst degradation rate is expected to increase membrane durability.

• Journal of IKEEE
• /
• v.22 no.4
• /
• pp.941-947
• /
• 2018

In general, capacitors have a large influence on the life of the system due to frequent charging and discharging. In this paper, we analyze the cause of the core failure of high voltage, high current HVDC sub-module film capacitor and analyze the precautions of the capacitor design and manufacturing process. First, the cause of the fault, the failure mode, and the effect are analyzed through the FMEA of the capacitor. To quantitatively evaluate the causes and effects of faults that have the greatest effect on the failure of a capacitor, a fault tree for the capacitor is presented and the failure rate is analyzed according to the design parameters and the driving conditions. It is verified that the main cause of capacitor failure is the capacitance change, and it is necessary to minimize the temperature rise, corona occurrence, electrode expansion, and insulation distance decrease during capacitor design and manufacturing process in order to reduce the failure rate of the capacitor.

• Journal of the Korean Electrochemical Society
• /
• v.18 no.2
• /
• pp.68-74
• /
• 2015

To compare the microstructure and electrochemical properties between two binary alloys (Cr-Si, Ni-Si), two composition of binary alloys with the same capacity were selected using phase-diagram and prepared by matrix-stabilization method to suppress the volume expansion of Si by inactive-matrix. Master alloys were made by Arc-melting followed by fine structured ribbon sample preparation by Rapid Solidification Process (RSP, Melt-spinning method) under the same conditions. Also powder samples were produced by wet grinding for X-Ray Diffraction (XRD) and electrochemical measurements. As predicted from the phase diagram, only active-Si and inactive-matrix ($CrSi_2$, $NiSi_2$) were detected. The results of Scanning Electron Microscope (SEM) and Transmission Electron Microscopy - Energy Dispersive X-ray Spectroscopy (TEM-EDS) show that Cr-Si alloy has finer microstructure than Ni-Si alloy, which was also predictable through phase diagram. The electrochemical properties related to microstructure were evaluated by coin type full- and half-cells. Separately, self-designed test-cells were used to measure the volume expansion of Si during reaction. Volume expansion of Cr-Si alloy electrode with finer microstructure was suppressed significantly and improved in cycle capability, in comparison Ni-Si alloy with coarse microstructure. From these, we could infer the correlation of microstructure, volume expansion and electrochemical degradation and these properties might be predicted by phase diagram.

• Proceedings of the Korean Institute of Surface Engineering Conference
• /
• 1998.05a
• /
• pp.60-60
• /
• 1998

아연도금강판은 내식성이 우수하여 자동차용 강판으로 널리 쓰이고 있다. 자동차용 강판은 spot 용접에 의해서 각 부분들이 접합되는데 도금층으로 사용되는 아연은 강판보다 융점이 낮아서 용접작업을 저하시킨다. 현재 사용되는 작업조건에서 용접 타 접수가 평균 2000회를 넘게되면 용접되는 부위의 면적이 감소되어 접합강도가 떨어지게된다. 따라서, 아연이 도금된 강판을 용접하게되면 작업성이 저하되므로 도금층의 성분에 대한 변화를 주므로서 이에 대한 개선을 할 필요가 있다.. Cole, Dickenson 및 Kimchi 등은 도금충내의 알루미늄을 0.1~0.5%(중량비) 함유하는 아연도금강판은 저항용접시 도금충내의 알루미늄 함량에 따라 용접성이 영향을 받는다고 보고하였다. 전극수명은 도금층내의 알루미늄 함량이 증가할수록 떨어지는데 알루미늄이 0.5% 이 하로 함유된 아연도금강판의 경우는 용접타접수가 2000~6000회에 이르르나 알루미늄 이 50%이상 함유된 합금도금강판은 200-600회에 불과한 것으로 나타난다. H. M Matsuda 등은 도금층의 알루미늄이 용접성에 영향을 미치는 이유로서 도금층의 용융 온도 변화를 지적하였다. 도금충내에 알루미늄의 함량이 높게되면 철과 아연의 확산에 의한 합금화 반응이 저하되어 도금층의 용융온도가 높아지지 못하므로 용접성이 나빠지게 된다. 본 연구에서는 아연도금욕의 조성은 기존의 상태로 유지하고 제3의 원소를 첨가하여 도금층에 함유되는 알루미늄의 양에 미치는 효과를 조사하였다. 도금층의 불성변화 및 그에 따른 내식성을 조사하였으며 도금층의 조직변화도 함께 관찰하였다. 아울러 첨가원소에 의한 도금욕의 특성도 평가하였다. 첨가원소에 의해서 도금충내의 알루미늄 함량은 감소하는 경향을 나타내었으며 도금층의 물성은 주어진 조성범위 내에서 별다른 변화를 나타내지 않았다.brittlement)기구도 제안되고 었다. 원전의 냉각수는 고 순도의 물이지만 수 처리 과정과 웅축기 배관의 누수로 인한 산소, $Cu^{2+},{\;}S_xO_6{\;}^{2-}(x=3~6)$ 등이 유입되어 오염되는데 이려한 오염물질들이 수 ppm정도 소량 포함된 경우 응 력부식민감도는 상당히 증가된다. 산성분위기 흑은 산소, $Cu^{2+}$, 등이 소량 포합된 산화성 분위기 그리고 sufur oxyanion 에 오염된 고온의 물에서 600 의 IGSCC 민감도는 예민화도가 증가할 수록 민감하여 304 의 IGSCC 와 매우 유사한 거동을 보인다. 본 강연에서는 304 와 600 의 고온 물에서 일어나는 IGSCC 민감도에 미치는 환경, 예민화처리, 합금원소의 영향을 고찰하고 이에 대한 최근의 연구 동향과 방식 방법을 다룬다.다.의 목적과 지식)보다 미학적 경험에 주는 영향이 큰 것으로 나타났으며, 모든 사람들에게 비슷한 미학적 경험을 발생시키는 것 이 밝혀졌다. 다시 말하면 모든 사람들은 그들의 문화적인 국적과 사회적 인 직업의 차이, 목적의 차이, 또한 환경의 의미의 차이에 상관없이 아름다 운 경관(High-beauty landscape)을 주거지나 나들이 장소로서 선호했으며, 아름답다고 평가했다. 반면에, 사람들이 갖고 있는 문화의 차이, 직업의 차 이, 목적의 차이, 그리고 환경의 의미의 차이에 따라 경관의 미학적 평가가 달라진 것으로 나타났다.corner$적 의도에 의한 경관구성의 일면을 확인할수 있지만 엄밀히 생각하여 보면 이러한 예의 경우도 최락의 총체적인 외형은 마찬가지로 $\ulcorner$순응$\lrcorner$의 범위를 벗어나지 않는다. 그렇기 때문에도 $\ulcorner$

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.25 no.4
• /
• pp.28-36
• /
• 2021

It is known that buried rebars inside concrete structures are protected from corrosion due to passive layer. It is very important to delay the timing of corrosion or evaluate a detection of corrosion initiation for the purpose of cost-beneficiary service life of a structure. In this study, corrosion monitoring was performed on concrete specimens considering 3 levels of cover depth(60 mm, 45 mm, and 30 mm), W/C(water to cement) ratio(40.0%, 50.0%, and 60.0%) and chloride concentration(0.0%, 3.5%, and 7.0%). OCP(Open Circuit Potential) was measured using agar-based socket type sensors. The OCP measurement showed the consistent behavior where the potential was reduced in wet conditions and it was partially recovered in dry conditions. In the case of 30 mm of cover depth for most W/C ratio cases, the lowest OCP value was measured and rapid OCP recovery was evaluated in increasing cover depth from 30 mm to 45 mm, since cover depth was an effective protection against chloride ion ingress. As the chloride concentration increased, the effect on the cover depth tended to be more dominant than the that of W/C ratio. After additional monitoring and physical evaluation of chloride concentration after specimen dismantling, the proposed system can be improved with increasing reliability of the corrosion monitoring.

• Journal of the Korean Electrochemical Society
• /
• v.26 no.1
• /
• pp.1-10
• /
• 2023

The cathode, which is one of the four major components of a lithium secondary battery, is an important component responsible for the energy density of the battery. The mixing process of active material, conductive material, and polymer binder is very essential in the commonly used wet manufacturing process of the cathode. However, in the case of mixing conditions of the cathode, since there is no systematic method, in most cases, differences in performance occur depending on the manufacturer. Therefore, LiMn₂O₄ (LMO) cathodes were prepared using a commonly used THINKY mixer and homogenizer to optimize the mixing method in the cathode slurry preparation step, and their characteristics were compared. Each mixing condition was performed at 2000 RPM and 7 min, and to determine only the difference in the mixing method during the manufacture of the cathode other experiment conditions (mixing time, material input order, etc.) were kept constant. Among the manufactured THINKY mixer LMO (TLMO) and homogenizer LMO (HLMO), HLMO has more uniform particle dispersion than TLMO, and thus shows higher adhesive strength. Also, the result of the electrochemical evaluation reveals that HLMO cathode showed improved performance with a more stable life cycle compared to TLMO. The initial discharge capacity retention rate of HLMO at 69 cycles was 88%, which is about 4.4 times higher than that of TLMO, and in the case of rate capability, HLMO exhibited a better capacity retention even at high C-rates of 10, 15, and 20 C and the capacity recovery at 1 C was higher than that of TLMO. It's postulated that the use of a homogenizer improves the characteristics of the slurry containing the active material, the conductive material, and the polymer binder creating an electrically conductive network formed by uniformly dispersing the conductive material suppressing its strong electrostatic properties thus avoiding aggregation. As a result, surface contact between the active material and the conductive material increases, electrons move more smoothly, changes in lattice volume during charging and discharging are more reversible and contact resistance between the active material and the conductive material is suppressed.

• 한국신재생에너지학회:학술대회논문집
• /
• 2010.06a
• /
• pp.143.1-143.1
• /
• 2010

고분자 전해질막 연료전지(Polymer Electrolyte Membrane Fuel Cell; PEMFC)는 수소를 이용하여 전기를 발생시키는 친환경적이고 이상적인 발전장치로 고효율과 높은 전류밀도를 가지며 그 응용분야가 다양하다. 저온에서 작동하는 PEM fuel cell은 전극에서 효과적인 산화환원반응을 위해 그 촉매로 활성이 우수한 Pt(Platinum)을 사용하고 있으나, Pt의 높은 가격은 연료전지의 상용화에 걸림돌이 되고 있다. 본 연구에서는 연료전지의 Pt/C 촉매 층에서 Pt의 분산성을 높여 Pt의 담지량을 줄이고 작동 중 발생하는 Pt의 응집 현상을 방지하여 Pt의 수명을 연장시킬 목적으로, Au(gold) 나노입자를 첨가한 Pt-Au/C 복합나노촉매를 제조하였다. 본 발표에서는 합성된 Pt-Au/C 복합촉매 중 Au 첨가량이 Pt 촉매의 활성에 미치는 영향을 조사하기 위하여, 복합촉매 중에 금속(Pt+Au)의 총 함량이 30 wt.%와 40 wt.% 인 Pt-Au/C 촉매에 대하여 각각 Au 첨가량을 변화시켜, cyclic voltammetry 법에 의해 Au 첨가 효과를 조사한 결과에 대하여 보고하고자 한다. Au 나노입자를 제조하기 위한 출발 물질로는 $HAuCl_4{\cdot}4H_2O$를 이용하였고 trisodium citrate와 $NaBH_4$를 환원제로 하여, 입경이 5~8 nm 인 Au 콜로이드를 제조하였다. Pt-Au/C 복합나노촉매를 제조하기 위하여 먼저 Au/C 복합분체가 제조되었다. 0.03g의 carbon이 첨가된 carbon 현탁액에 합성된 Au 콜로이드 수용액을 첨가한 후 24시간 동안 교반하여 Au/C 복합분체를 제조하였다. 이 Au/C 복합분체에 $H_2PtCl_6{\cdot}6H_2O$ 수용액을 현탁하고 methanol 을 환원제로 사용해 Pt를 환원 석출시켜 Pt-Au/C 복합촉매를 제조하였다. Pt-Au/C 복합 나노촉매에서 Pt와 Au를 다양한 비율(3:1, 2.5:1.5, 2:2)로 합성하였으며 Pt-Au/C 복합촉매 중 금속(Pt+Au) 촉매의 총 함량은 30 wt.%와 40 wt.%로 각각 제조되었다. Au 나노입자 콜로이드의 분산성은 UV-visible spectrum의 흡광도에 의해 관찰되었고, Pt-Au/C 복합 나노촉매의 형상 및 분산성 분석은 transmission electron microscopy(TEM)에 의해 이루어졌다. 또한, 촉매의 전기화학적 특성평가는 cyclic voltammetry(CV)에 의해 조사되었다.

• Korean Chemical Engineering Research
• /
• v.55 no.2
• /
• pp.242-246
• /
• 2017

The application of composite cathode materials including $LiFePO_4$ (lithium iron phosphate) of olivine crystal structure, which has high thermal stability, were investigated as alternatives for hybrid battery-capacitors with a $LiMn_2O_4$ (spinel crystal structure) cathode, which exhibits decreased performance at high temperatures due to Mn-dissolution. However, these composite cathode materials have been shown to have a reduction in capacity by conducting life cycle experiments in which a $LiFePO_4$/activated carbon cell was charged and discharged between 1.0 V and 2.3 V at two temperatures, $25^{\circ}C$ and $60^{\circ}C$, which caused a degradation of the anode due to the lowered voltage in the anode. To avoid the degradation of the anode, composite cathodes of $LiFePO_4/LiMn_2O_4$ (50:50 wt%), $LiFePO_4$/activated carbon (50:50 wt%) and $LiNi_{1/3}Co_{1/3}Mn_{1/3}O_2$ (50:50 wt%) were prepared and the life cycle experiments were conducted on these cells. The composite cathode including $LiNi_{1/3}Co_{1/3}Mn_{1/3}O_2$ of layered crystal structure showed stable voltage behavior. The discharge capacity retention ratio of $LiNi_{1/3}Co_{1/3}Mn_{1/3}O_2$ was about twice as high as that of a $LiFePO_4/LiMn_2O_4$ cell at thermal stability experiment for a duration of 1,000 hours charged at 2.3 V and a temperature of $80^{\circ}C$.