• Journal of Electrochemical Science and Technology
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• 제12권1호
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• pp.67-73
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• 2021

Nickel-rich lithium nickel-cobalt-manganese oxides (NCM) are viewed as promising cathode materials for lithium-ion batteries (LIBs); however, their poor cycling performance at high temperature is a critical hurdle preventing expansion of their applications. We propose the use of a functional electrolyte additive, triphenyl phosphate (TPPa), which can form an effective cathode-electrolyte interphase (CEI) layer on the surface of Ni-rich NCM cathode material by electrochemical reactions. Linear sweep voltammetry confirms that the TPPa additive is electrochemically oxidized at around 4.83 V (vs. Li/Li+) and it participates in the formation of a CEI layer on the surface of NCM811 cathode material. During high temperature cycling, TPPa greatly improves the cycling performance of NCM811 cathode material, as a cell cycled with TPPa-containing electrolyte exhibits a retention (133.7 mA h g-1) of 63.5%, while a cell cycled with standard electrolyte shows poor cycling retention (51.3%, 108.3 mA h g-1). Further systematic analyses on recovered NCM811 cathodes demonstrate the effectiveness of the TPPa-based CEI layer in the cell, as electrolyte decomposition is suppressed in the cell cycled with TPPa-containing electrolyte. This confirms that TPPa is effective at increasing the surface stability of NCM811 cathode material because the TPPa-initiated POx-based CEI layer prevents electrolyte decomposition in the cell even at high temperatures.

• Current Applied Physics
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• 제18권11호
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• pp.1345-1351
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• 2018

To allow stable cycling of layered nickel-rich cathode material at high voltage, silyl-functionalized dimethoxydimethylsilane is proposed as a multi-functional additive. In contrast to typical functional additive, dimethoxydimethylsilane does not make artificial cathode-electrolyte interfaces by electrochemical oxidation because it is quite stable under anodic polarization. We find that dimethoxydimethylsilane mainly focuses on scavenging nucleophilic fluoride species that can be produced by electrolyte decomposition during cycling, leading to improving interfacial stability of both nickel-rich cathode and graphite anode. As a result, the cell cycled with dimethoxydimethylsilane-controlled electrolyte exhibits 65.7% of retention after 100 cycle, which is identified by systematic spectroscopic analyses for the cycled cell.

• 한국정보통신학회:학술대회논문집
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• 한국정보통신학회 2015년도 추계학술대회
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• pp.397-400
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• 2015

본 논문에서는 낮은 듀티 동작의 센서 노드를 위한 저비용 MPPT 제어기능을 갖는 빛에너지 하베스팅 회로를 제안한다. 환경, 구조물 모니터링 센서와 같은 연속적인 동작이 요구되지 않는 센서 노드가 어플리케이션이며, 기존의 MPPT(Maximum Power Point Tracking) 제어방법과 다르게 간단한 회로들을 이용하여 저비용 MPPT 제어 방법을 구현하였다. 제안된 MPPT 방법은 솔라셀의 개방회로전압과 MPP 전압간의 비례관계를 이용하여, 솔라셀의 개방회로 전압을 주기적으로 샘플링함으로써 최대 가용전력이 생성되는 지점을 추적하고 이를 부하로 전달한다. 제안된 회로는 $0.35{\mu}m\;CMOS$ 공정으로 설계되었으며, 칩 면적은 패드를 포함하여 $975{\mu}m{\times}1025{\mu}m$이다. 제작된 칩을 측정한 결과 주기적으로 솔라셀의 개방회로를 샘플링하여 솔라셀의 MPP를 실시간 추적하는 것을 확인하였다.

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

• 대한전기학회논문지
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• 제40권9호
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• pp.883-892
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• 1991

This paper presnets the characteristics of electropolymerization and electrochemicla propoerties of polyaniline(PAn). From the morphology study on the PAn surface, it seems that coagulation of the fibrils on the surface proceeds as the PAn grows, resulting in fibril clusters with new branches and more extensive voids. While PAn/Li cell is cycled at potential range between 2.9V and 3.7V in which the first strong reduction peak of 2.75V does not appear, its oxidation reduction capacities were increased up to about tenth cycle. Electricity efficiency of stable charge-discharge to deep discharge in PAn/Li cell was 42.9%. Average charge potential, avergae discharge potential, energy density, and charge-discharge energy efficiency of the PAn/Li cell were 3.4V, 3.25V, 132.9Wh/kg, and 95.6%, respectively.

• 전기화학회지
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• 제26권1호
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• pp.11-18
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• 2023

전기자동차 시장의 급속한 성장으로 이차전지의 사용이 급증함에 따라 사용 후 전지의 폐기 및 재활용이 심각한 문제로 제기되고 있다. 사용 후 리튬이온 전지를 처리하기 위해서는 저장된 에너지를 제거하기 위하여 효과적으로 방전하는 과정이 필수적이다. 본 연구에서는 흑연과 LiNi_0.6Co_0.2Mn_0.2O₂ (NCM622)을 사용하여 코인셀 형태로 반쪽전지 및 완전지를 제조하였고, 이를 과방전할 때 발생하는 전기화학적 거동에 대하여 분석하였다. 반쪽전지를 사용하여 양극과 음극을 각각 과방전시키면, 양극에서는 먼저 전이금속 산화물이 금속으로 환원되는 전환반응을 겪게 되며, 음극에서는 SEI 피막의 분해에 이어 집전체인 Cu가 용출되는 부반응이 발생하였다. 또한, 이러한 과방전의 발생 시에는 큰 분극을 필요로 하였다. 완전지의 과방전 시에는 각각의 부반응이 진행되는 시점에 존재하는 큰 분극들로 인하여 부반응의 본격적인 발생 전에 0 V에 도달하여 방전이 종료되었다. 그러나, 사이클을 통하여 용량이 퇴화된 완전지의 경우에는 과방전거동이 변화하여 음극에서 Cu 집전체의 부식이 발생됨을 확인하였다. 따라서, 사용 후 전지는 사용 전의 전지와는 과방전 시에 다른 거동을 지니고 있으므로 이러한 점들이 고려되어야 한다.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1996년도 봄 학술발표회 논문집
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• pp.348-353
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• 1996

This study addresses the evaluation of the durability of reinforced concrete marine structures subjected to fatigue loading. The laboratory investigation was carried out on full and half size reinforced concrete specimens with three different water cement ratios (0.3, 0.4, and 0.56), static and fatigue loading conditions, and epoxy-coated and regular black steel reinforcements. The marine tidal zone was simulated by alternate filling and draining of the tank (wet and dry cycled), and a galvanostatic corrosion technique to accelerate corrosion of reinforcement was used. Half-cell potentials and changes of crack width were measured periodically during the exposure and followed by ultimate strength testing. The significant findings include adverse effect of fatigue loading, existence of an explicit size effect, poor performance of epoxy coated steel, and negative effect of increasing water/cement ratio.

• Tuberculosis and Respiratory Diseases
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• 제81권2호
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• pp.148-155
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• 2018

Background: Although targeted therapy and immuno-oncology have shifted the treatment paradigm for lung cancer, platinum-based combination is still the standard of care for advanced non-small cell lung cancer (NSCLC). Pemetrexed continuation maintenance therapy has been approved and increasingly used for patients with nonsquamous NSCLC. However, the efficacy of this strategy has not been proven in patients without driving mutations. The objective of this study was to compare the clinical benefit of pemetrexed continuation maintenance to conventional platinum-based doublet in epidermal growth factor receptor (EGFR)-negative lung adenocarcinoma. Methods: A total of 114 patients with EGFR-negative lung adenocarcinoma who were treated with platinum doublet were retrospectively enrolled. We compared the survival rates between patients received pemetrexed maintenance after four-cycled pemetrexed/cisplatin and those received at least four-cycled platinum doublet without maintenance chemotherapy as a first-line treatment. Results: Forty-one patients received pemetrexed maintenance and 73 received conventional platinum doublet. Median progression-free survival (PFS), which was defined as the time from the day of response evaluation after four cycles of chemotherapy to disease progression or death, was significantly higher in the pemetrexed maintenance group compared to conventional group (5.8 months vs. 2.2 months, p<0.001). Median overall survival showed an increasing trend in the pemetrexed maintenance group (22.3 months vs. 16.1 months, p=0.098). Multivariate analyses showed that pemetrexed maintenance chemotherapy was associated with better PFS (hazard ratio, 0.73; 95% confidence interval, 0.15-0.87). Conclusion: Compared to conventional platinum-based chemotherapy, premetrexed continuation maintenance treatment is associated with better clinical outcome for the patients with EGFR wild-type lung adenocarcinoma.

• 대한기계학회논문집A
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• 제39권6호
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• pp.639-644
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• 2015

원형 리튬 전지는 노트북, 파워툴이나 전기 자동차와 같이 고용량/고율 방전이 필요한 분야에서 널리 사용되는 이차전지 중의 하나로 저장된 화학 에너지를 전기화학적 반응을 통해 전기 에너지로 변환하는 장치이다. 센터 핀은 원형 리튬 전지 내에 가스 분출 채널 확보를 위해 젤리-롤 중심홀이 충/방전 중 좁혀지는 것을 방지하고, 낙하 충격 시 완충 작용으로 분리막 손상을 방지하여 내부 단락을 막아주는 역할을 담당하는 부품이다. 본 연구에서는 센터 핀의 중요한 역할들에 대해 실험적으로 검증하기 위해서 센터 핀 유/무에 따른 2 가지 실험을 진행하였다. 하나는 연속 50 회 충/방전 싸이클 후의 젤리-롤 중심홀의 변화이고, 다른 하나는 UL 표준 기준에 의한 자유 낙하 충격 실험을 통한 젤리-롤 내 분리막 손상에 의한 내부 단락 여부이다. 이러한 실험적 결과를 바탕으로 원형 전지의 센터핀이 안전성 측면에서 반드시 필요한 부품임을 확인할 수 있었다.

• 한국전기전자재료학회논문지
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• 제19권7호
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• pp.650-654
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• 2006

[ $LiNi_{0.4}Mn_{0.3}Co_{0.3}O_2$ ] cathode material was synthesized by a mixed hydroxide method. Structural characterization was carried out using X-ray diffraction studies. Electrochemical studies were performed by assembling 2032 coin cells with lithium metal as an anode. DSC (Differential scanning calorimetry) data showed that exothermic reactions of $LiNi_{0.4}Mn_{0.3}Co_{0.3}O_2$ charged to 4.3 V versus Li started at high temperatures$(280\sim390^{\circ}C)$. The cell of $LiNi_{0.4}Mn_{0.3}Co_{0.3}O_2$ mixed cathode delivered a discharge capacity of 150 mAh/g at a 0.2 C rate. The capacity of the cell decreased with the current rate and a useful capacity of 134 mAh/g was obtained at a 2 C rate. The reversible capacity after 100th cycles was 126 mAh/g when a cell was cycled at a current rate of 0.5 C in $2.8\sim4.3V$.