Engineering of tungsten oxide nanoarchitectonics as a dual-function material for electrochromic energy storage applications

Pritam J., Morankar 영남대학교 대학원 2024 국내박사

Designing and fabrication of carbon electrode for advanced energy storage devices

이수찬 Graduate School, Yonsei University 2021 국내박사

The advanced energy storage device has become a prime area of research to solve both serious environmental problems such as global fossil fuel consumption and customer demands for high energy devices for portable electronic. The outstanding performance such as large energy density of lithium ion battery (LIB) makes itself a most powerful energy storage device. However, LIB has some growing concerns about cost due to its limited reserves of raw materials. The intrinsic drawbacks of LIBs such as low power density and risk of explosion limits their applications in some areas. Thus, current device configuration of LIBs with cofacial film type is not suitable for flexible and wearable device because it is vulnerable to bending stress and has risk of short circuit. Despite these shortcomings, LIBs still have excellent performance, and developing energy storage devices with all characteristics superior to LIBs is difficult with current technology. To overcome these limitations, advanced energy storage device optimized for specific applications should be developed. The characteristics of electrode largely dictate the overall performance of electrochemical energy storage device. The carbonaceous materials are the most widely used electrode materials for electrochemical energy storage devices due to its characteristics such as earth abundant, high conductivity and varieties of morphologies. In this thesis, I suggested designing and fabrication method of carbon electrodes for high energy density, coplanar battery/supercapacitor sodium ion batteries (SIB) and as advanced energy storage devices. The carbon material can be used not only as an active material, but also as a current collector. Compared to metal foil current collector, carbon current collector has own advantages such as light weight and chemical stability. Herein, I suggested 3D graphene electrode for ultrahigh capacitance supercapacitor. 3D graphite with skeleton type structure can enhance the electrochemical reaction by large surface area and decrease total weight of supercapacitor electrode. In the case of a patterned electrode located on coplanar, it is resistant to bending stress in a specific direction, and there is no risk of short circuit because the anode cathode is physically separated. Therefore, it has attracted much attention as an electrode for a flexible/wearable battery. In this study, the development of a carbon material-based micro-supercapacitor and a flexible lithium ion battery was conducted using the patterned electrode. For the production of carbon-based micro supercapacitors, I developed graphene oxide patterning technology that shows excellent supercapacitor performance. In the development of flexible lithium-ion batteries, graphite, which is the most representative negative electrode material, was used to prepare high performance flexible batteries. The binder-assisted electrostatic spray deposition was developed to solve the problem of difficulty in patterning due to the large particle size of graphite, and succeeded in manufacturing flexible lithium-ion batteries. Sodium, an earth abundant metal, can be a reasonable alternative to lithium especially for large-scale energy storage applications. SIBs have similar working principle with that of LIBs, which makes the development of SIBs uncomplicated. However, many materials have been studied for SIB electrode, but only a few materials achieve a certain level of performance even though those candidate materials already showed good lithium ion storage performance. Especially in case of anode, the graphite was most powerful LIB anode material with low price and good performance but it has very low capacity with sodium ion. Hence, mechanical activation method for graphite to enhance the capacity of graphite in SIB is suggested. Furthermore, the energy storage mechanism of activated graphite is symmetrically investigated with advanced analysis tools. I revealed that unexpected reversible reaction at surface of solid electrolyte interphase, which can contribute to reversible capacity. By ex-situ XPS depth analysis, the bulk reaction in disordered carbon particle is attributed from reversible Na-O compound formation. Based on these analysis results, the optimized mechanically activated graphite was prepared with high reversible capacity and long cycle stability at high current density. These studies aim to allow the designing and fabrication of carbon based electrode for advanced energy storage devices. 차세대 에너지 저장 장치는 전세계적인 화석 연료 고갈, 지구 온난화 등 환경 문제의 대두와 고성능의 휴대용 전자 기기에 대한 소비자들의 요구가 커지면서 점차 연구 중점 분야가 되어가고 있다. 리튬 이온 배터리는 높은 에너지 밀도 등 우수한 특성으로 인해 가장 널리 이용되고 있는 에너지 저장 장치 기술이다. 하지만 리튬은 매장량이 많이 않으며 매장 지역 또한 고르게 분포 되어 있지 않다. 따라서 장기적인 전망에서 리튬 이온 배터리의 원자재 가격은 크게 상승할 것으로 예상된다. 또한 낮은 출력 밀도, 잠재적인 폭발 위험성 그리고 낮은 수명 특성 등 현재 리튬 이온 배터리가 가지고 있는 단점들 또한 리튬 이온 배터리가 새로운 적용 분야를 개척하기 힘들게 만들고 있다. 또한 현재의 리튬 이온 배터리는 양극과 음극이 서로 마주보는 적층형 필름 구조로 제작 되는데 이는 굽힘 응력에 취약하고 양극과 음극 사이의 단락의 위험성이 있어 유연 전지로의 활용이 어렵다는 단점이 있다. 하지만 이러한 단점 들에도 불구하고 여전히 리튬 이온 배터리는 다른 대안 기술 대비 우수한 특성들을 보이고 있으며 현재 기술로는 모든 핵심 특성이 리튬 이온 배터리 보다 뛰어난 기술 개발은 힘든 상황이다. 따라서 이를 해결하기 위해 차세대 에너지 저장 장치 개발은 적용 될 장치가 요구하는 핵심 특성을 극대화 한 방향으로 연구되어야 한다. 전기화학적 에너지 저장 장치의 특성은 사용 된 전극의 성능에 큰 영향을 받는다. 다양한 전극 소재 중에서 탄소 기반 소재의 경우 매장량이 많고, 전도성이 우수하며, 형상의 다양성 등 여러 우수한 특성으로 인해 가장 널리 이용되고 있는 소재 중 하나이다. 따라서 본 논문에서는 탄소 소재 기반으로 차세대 고성능 에너지 저장 장치 전극 개발을 목표로 연구를 진행하였다. 탄소 소재는 배터리/슈퍼캐패시터 분야에서 활물질로만 사용될 수 있는 것이 아닌, 집전체로도 사용가능하다. 탄소 집전체의 경우, 기존 금속 집전체 대비 무게가 가볍다는 장점 및 화학적 안정성이 뛰어나다는 장점이 있다. 따라서 본 연구에서는, 슈퍼캐패시터의 집전체로 3 차원 그래핀을 적용하여 높은 용량의 슈퍼캐패시터 제조에 성공하였다. 이는 3 차원 그래핀의 높은 비표면적, 우수한 전기 전도성 및 코발트 수산화물과의 우수한 접촉 구조 등에 의한 결과로서 향후 슈퍼캐패시터 전극 개발에 있어 새로운 방향을 제시할 수 있을 것으로 기대된다. 동일평면상에 위치한 패터닝 된 전극의 경우 특정 방향에 대해 굽힘 응력에서 자유롭고 양극 음극이 물리적으로 분리되어 있어 단락의 위험성이 없다. 따라서 유연 전지, 웨어러블 전지 용 전극으로 많은 주목을 받고 있으며 본 연구에서는 이러한 패턴 된 전극을 이용해 탄소 소재 기반 마이크로 슈패캐패시터 및 유연 리튬 이온 전지 개발을 진행하였다. 탄소 소재 기반의 마이크로 슈퍼캐패시터 제작을 위해 뛰어난 슈퍼캐패시터 성능을 보이는 산화 그래핀의 패터닝 기술을 개발하였다. 유연 리튬 이온 전지 개발에서는 가장 대표적인 음극 소재인 흑연을 이용하였으며 흑연의 큰 입자 크기로 인해 패터닝이 힘들하는 문제를 해결하기 위해 고분자를 이용한 스프레이 코팅 방식을 개발, 유연 리튬 이온 배터리 제조에 성공하였다. 소듐은 지구상에서 6 번째로 매장량이 많은 물질 중 하나로서 가격이 저렴하여 대용량 배터리 시장에서 리튬 이온을 대신할 수 있는 후보 중 가장 주목을 받고 있다. 소듐 이온 전지의 작동 원리는 리튬 이온 전지와 거의 동일하며 이 동일성으로 인해 소듐 이온 전지의 개발이 리튬 이온 전지의 개발과 동일한 방식으로 이루어지고 있다. 하지만 구동 방식은 동일하지만 리튬 이온 전지에서 우수한 특성을 보였던 많은 소재들이 소듐 이온 전지에서는 좋지 않는 특성을 보이는 것으로 보고 되었다. 특히, 음극 소재의 경우 리튬 이온 전지의 성공을 이끌었던 흑연이 기존의 전해질과는 매우 낮은 가역 용량을 나타내는 것으로 보고되어 이를 대체할 수 있는 새로운 물질 개발이 시급한 상황이다. 하지만 다른 대체물질들은 원재료 가격이 흑연보다 비싸 소듐 이온 전지의 가장 큰 장점인 가격 경쟁력의 확보를 위해서는 탄소 기반의 소듐 이온 전지 음극 소재 개발이 필수적이다. 본 연구에서는 흑연의 기계적 활성화 방법을 개발하여 소듐 이온 저장 능력 활성화 방법에 대해 보고 하였다. 또한 활성화 된 흑연의 소듐 이온 저장 매커니즘을 분석하기 위해 다양한 분석을 수행하였으며 그 결과 탄소 표면 및 내부에서의 각각 다른 반응을 보이는 것을 확인하였다. 최종적으로 잠재적인 매커니즘을 제시하였다.

Synthesis of Zinc Oxide Nanoparticles using Terminalia ferdinandiana (Kakadu Plum) Extract and Its Biological Activities

안종찬 경희대학교 대학원 2023 국내박사

Terminalia ferdinandiana (Kakadu plum) is an Australian native plant that has recently gained the attention of researchers due to its high antioxidant compounds that have substantial health benefits. It is a commercially important antioxidant as it contains a more eloquent level of ascorbic acid than other oranges. In this study, we analyzed the chemical constituents such as vitamin C, gallic acid, egallic acid, and daidzin via HPLC of the Kakadu plum from two different regions including the northern territory (NT) and western Australia (WA), and compare their biochemical properties. The plant was screened for potential drug usage in fatty liver disease treatment that the plant had a vitamin C content much higher (almost 70 %) in Kakadu plum from NT than in WA. And the ZnO NPs was synthesized using plant extract for checking any anticancer and anti-inflammatory activity. Moreover, during treatment of HepG2 cells (human hepatoma cells) with the KKD-NT extract suppressed ROS generation more significantly than KKD-WA extract. The cytotoxicity induced by the treatment of ethanol was significantly suppressed in response to treatment with both of the samples. The vitamin C content was much higher (almost 70 %) in Kakadu plum from NT than WA. Moreover, treatment of HepG2 cells (human hepatoma cells) with the KKD-NT extract has suppressed ROS generation more significantly than KKD-WA extract. The cytotoxicity induced by the treatment of ethanol was significantly suppressed in response to treatment with both of the samples. Further, to evaluate anticancer and anti-inflammatory activity, the ZnO NPs using the Kakadu plum extract was synthesized and it showed higher anti-lung cancer activity that represents it as a potential anticancer drug. The formation of KKD-ZnO-NPs (ZnO particles obtained from Kakadu plum) were confirmed using a UV-Visible spectrophotometer. Fourier transforms infrared (FTIR) spectroscopy analysis confirmed the functional groups that are responsible for the stabilization and capping of KKD-ZnO-NPs. The flower shape of the synthesized KKD-ZnO-NPs was confirmed by field emission-scanning electron microscopy (FE-SEM) and field emission-transmission electron microscopy (FE-TEM) analyses. The crystallites were highly pure and had an average size of 21.89 nm as measured by X-ray diffraction (XRD). The dynamic light scattering (DLS) revealed the size range of polydisperse KKD-ZnO-NPs was 676.65 ± 47.23 nm with a PDI of 0.41 ± 0.0634. the potential cytotoxicity was investigated in vitro against human lung cancer cell lines (A549) and Raw 264.7 Murine macrophage cells as normal cells to ensure safety purposes using MTT assay. Thus, KKD-ZnO-NPs showed prominent cytotoxicity against human lung adenocarcinoma (A549) at 10 μg/mL and increased reactive oxygen species (ROS) production as well, which could promote toxicity to cancer cells. Moreover, the up regulation of p53 and down regulation of bcl2 gene expression as apoptosis regulators were confirmed via RT-PCR. In addition, KKD-ZnO-NPs possess a similar capacity of reduction in proinflammatory-nitric oxide (NO) production when compared to the NG-Methyl-L-arginine, acetate salt (L-NMMA) as an inflammation inhibitor that can be used potential anti-inflammatory agent. Moreover, the plant has a high potential for liver disease as well as can have a potential nanodrug for lung cancer and inflammation.

Facile synthesized nanoporous Si/C as an anode material for lithium ion batteries

민찬우 Chonnam National University 2019 국내석사

리튬 이온 배터리 (LIB)는 휴대용 장치 및 전기 자동차 (EV)에 주로 사용하고 있다. LIB를 위한 가장 대표적인 상업용 음극 재료는 흑연입니다. 그러나, 낮은 이론 용량 (372 mAh g-1) 및 속도 성능은 EV 및 대형 ESS에 사용하기에 충분하지 않다. 실리콘(Si)은 높은 이론 용량 (Li15Si4의 경우 3600 mAh g-1), 낮은 작동 전위 (0.4 V vs. Li / Li +), 저렴한 비용, 풍부한 자원량, 낮은 독성을 가지고 있으며, 친환경적이기 때문에 유망한 LIB 음극소재로 사용될 수 있다. 그러나, LIB의 Si 기반 음극은 다음과 같은 몇 가지 단점을 보인다. Li 이온과 합금하는 동안 Si은 약 3배 이상의 큰 부피 팽창을 하기 때문에 활성 물질의 균열 및 전극의 용량 감소를 야기시킨다. Si 전극은 흑연과 비교하여 낮은 고유 전기 전도도를 갖는다. 또한, Si가 유기 전해질에 노출 될 때 고체 전해질 계면 (SEI) 층이 안정적이지 않아 전해질의 분해 및 낮은 쿨롱 효율을 유도한다. 최근, 우리는 매우 간단하고 빠르게 마그네슘 열 환원 방법을 이용하여 나노 다공성 Si 분말을 합성하는 공정을 보고한 바 있다. 대기 중에서 저비용으로 빠르고 간편하게 마그네슘 환원 공정을 사용할 수 있다는 것이 두드러진 특징이다. 본 연구에서는 준비된 다공성 나노 크기의 Si 전극의 전도도와 SEI 층의 안정성을 향상시키기 위해 탄소 코팅을 시도하였다. 시트르산 전구체로부터 다양한 양의 탄소를 쉬운 졸-겔법을 통해 섞어준 후 탄화 공정을 통해, 나노 다공성 Si/C 복합체를 제조하였다. XRD, FE-SEM, TEM, Raman spectroscopy, 그리고 TGA를 이용하여 합성 된 Si/C 복합 재료의 형태, 불순물 여부 및 탄소 존재와 함량을 분석 하였다. 합성 된 Si/C 입자는 3D 상호 연결된 Si/C 구조를 형성함으로써 260.7 m2 g-1의 높은 표면적과 10.73 nm의 평균 기공 크기를 나타냈다. 또한 Si/C 전극의 전기 화학적 특성은 전기 화학 임피던스 분광법 (EIS), 순환 전압 전류 법 및 정전류 충 방전 시험으로 분석 하였다. Si/C 전극은 전류 밀도 0.36 A g-1에서 초기 쿨롱 효율 76%를 나타내었으며, 100 사이클 후에 82%의 가역 용량 보전율을 보이고, 2274 mAh g-1의 높은 가역 용량을 나타내었다. 또한, Si/C 전극은 순수한 Si 전극에 비해 36 A g-1의 매우 높은 전류 밀도에서도 더 나은 사이클 안정성과 가역 용량 값을 보였고, 더 낮은 저항 값을 보였습니다. 이러한 결과는 탄소 코팅이 Si/C 전극의 안정성 및 전기 전도성을 향상시켰다는 것을 명백하게 나타낸다. Currently, Li-ion batteries (LIBs) have been mainly used for portable devices and electric vehicles (EVs). The most representative commercial anode material for LIBs is graphite. Unfortunately, its low theoretical capacity (372 mAh g−1) and rate capability are not sufficient to be used for EVs and large-scale energy storage systems (ESSs). Silicon is a promising anode material for LIBs due to its large theoretical capacity (3600 mAh g-1 for Li15Si4), low working potential (< 0.4 V vs. Li/Li+), low cost, large amount resources, low toxicity, and environmental friendliness. However, Si based anodes in LIBs have several drawbacks. During alloying with Li, Si exhibits large volume expansion of >300%, leading to cracking of the active materials and capacity decay. Si electrode also has low intrinsic electrical conductivity compared with graphite. In addition, solid electrolyte interface (SEI) layer is not stable when Si is exposed to organic electrolytes, leading to the decomposition of electrolyte and low coulombic efficiency. Recently, we reported an ultra-simple Mg-thermal-reduction method for nanoporous Si powders. It is noticeable that simple Mg-reduction process can be used at low cost in ambient air. In the present work, we employed carbon coating to improve the conductivity of prepared porous nano-sized Si electrode and the stability of SEI layer. We prepared a nano-porous Si/C composite through a facile sol-gel route with various amounts of carbon from citric acid precursor. The morphology, phase purity, and presence of carbon in the synthesized Si/C composites were analyzed by XRD, FE-SEM, TEM, and Raman spectroscopy. The synthesized Si/C particles exhibited a high surface area of 260.7 m2 g-1 and an average pore size of 10.73 nm by forming 3D-interconnected Si/C structures. Furthermore, electrochemical characteristics of Si/C electrode was analyzed by electrochemical impedance spectroscopy (EIS), cyclic voltammetry, and galvanostatic charge-discharge test. The Si/C electrode showed a high reversible capacity of 2274 mAh g-1 with initial coulombic efficiency of 76% and a capacity retention of 82% after 100 cycles at the current density of 0.36 A g-1. In addition, the Si/C electrode showed better cycle stability even at pretty high current density of 36 A g-1 and lower impedance values compared to pure Si electrode. These results indicate that carbon coating attributed to improve stability and electrical conductivity of the Si/C electrode.

감산형 간섭 제거 방식을 적용한 터보 부호화 CDMA 시스템

권혁찬 Graduate School, Yonsei University 2001 국내박사

Investigations into cranks of partitions, trigonometric sums, and Q-integrals

Chan, O-Yeat University of Illinois at Urbana-Champaign 2006 해외박사(DDOD)

소속기관이 구독 중이 아닌 경우 오후 4시부터 익일 오전 9시까지 원문보기가 가능합니다.

In this dissertation, we apply the Hardy-Ramanujan-Rademacher circle method to find asymptotic formulas for sequences generated by certain quotients of theta functions related to cranks of partitions. These formulas allow us to prove conjectures of B. C. Berndt, H. H. Chan, S. H. Chan, and W. C. Liaw regarding monotonicity of these sequences, as well as to prove the completeness of tables of values for these sequences found on pages 179 and 180 of Ramanujan's Lost Notebook. We also prove a conjecture of G. E. Andrews and R. Lewis regarding the signs of the difference of the number of partitions of a number n with crank congruent to 0 modulo 4 minus the number of partitions of n with crank congruent to 2 modulo 4. We also use contour integration to derive formulas for evaluating sums of odd or even periodic functions, weighted by any sequence of complex numbers, summed over a half-period. We specialize our formulas to sums of quotients of trigonometric functions, weighted by the positive integers, the characteristic function of a congruence class modulo n, and real primitive Dirichlet characters. We also prove two theta function identities that generalize identities found by Z.-G. Liu. From these two identities, we derive evaluations for two trigonometric sums by taking a limit. Finally, we prove generalizations of integrals found on page 201 of Ramanujan's Lost Notebook. We also prove several results related to the integrals on page 201. Our integral evaluations follow from well-known product-series identities from the theory of q-series.

(A)lexical approach to word order variation in korean : by Chan Chung

Chung, Chan Ohio State Univ. 1995 해외박사

하나의 절안에서 일어나는 어순자유변동 (Clause-internal Scrambling) 과 절의 범위를 넘어서 일어나는 장거리 어순자유변동 (long-distance scram bling)은 통사적으로 서로 구분되지 않으며, 따라서 이들 현상은 하나의 방 법으로 설명되어야 한다. 이 두가지 유형의 어순변동은 평면 절구조 (Flat clause structure)에서 핵이 아닌 구성성분 (non-head constituents)사이에 적용되는 어순제약이 상대적으로 자유스러움에서 기인된다. 장거리 어순 자유변동과 관련된 중요한 장치는 논항 및 첨가어의 유입 (argument and adjunct attraction)인데, 이것은 지배받는 내포동사의 주어, 보어, 첨가어가 그 동사를 지배하는 주동사의 주어목록, 보어목록, 첨가어목록으로 유입 또 는 상승 (attracted or raised)되는 장치를 말한다.

Artificial Induction of Biological Soil Crust for Combating Against Desertification

CHAN-HO PARK 순천대학교 대학원 2015 국내박사

Desertification is a major concern in the current era and a vast region of soil is already been devastated in several countries in the arid zones. Combined application of cyanobacteria with soil fixing chemical is one of the novel method to revegetate the desertified area in a systematic process. Cyanobacteria and soil fixing chemicals were applied to sand materials under laboratory and field conditions. In our present study, three cyanobacteria, Nostoc sp. Vaucher ex Bornet & Flahault, Phormidium sp. Kützing ex Gomont and Scytonema arcangeli Bornet ex Flahault were employed. Polyvinyl alcohol (PVA) and Tacki-SprayTM (TKS7) chemicals were examined to stabilize the soil particles. In addition, superabsorbent polymer (SAP) was applied as a water-holding material and nutrient supplement in soil. Mean weight diameter values demonstrated that the minimal cell concentration for the induction of artificial cyanobacterial crust was 10 mg FW cm-2, and the resulting soil crust was stable enough to resist various destructive factors. Moreover, combined application of cyanobacteria with different concentrations of TKS7 (0.5-2.5 mg cm-2) enhanced soil aggregate stability, resulting in mean weight diameter values of 0.58–0.69 mm, which was comparable to single application of TKS7 (0.18–0.40 mm). Interestingly, surface hardness values were also highly improved by the combined application compared to single treatments. Although addition of SAP slightly reduced the aggregate stability and surface hardness, it improved the growth of cyanobacteria. On the basis of these results, field experiments were conducted in the Shapotou desert, China. Application of cyanobacteria with superabsorbent polymer and TKS7 (CST) remarkably improved the soil aggregate stability against water and wind erosion during 12 months of induction. Comparative studies with the approximately 20-year-old natural cyanobacterial crust (N-BSC) revealed that the mean weight diameter and threshold friction velocity were increased by 75% and 88% respectively; while single treatment of cyanobacteria (CY) resulted in 68% and 73%. Apparently, in spite of addition of soil fixing chemical, the biological activities of CST was significantly similar with CY. Furthermore, biological activities, such as extracellular polysaccharide, cyanobacterial biomass, microbial biomass, soil respiration, carbon fixation and effective quantum yield dramatically increased by effective quantum yield dramatically increased by 50-100% of N-BSC, while those of control soil were negligible. In view of aforementioned results, it can be concluded that the combined application of cyanobacteria with soil fixing chemical can rapidly induce cyanobacterial BSC formation in the field within a span of 12 months without any damages. The physical properties and biological activities of soil have been maintained or improved. The novel method presented herein makes it feasible and serves as an alternative strategy for combating desertification in arid regions.

Diffusion of rototiliers in rural Korea to 1977 : by Chan Suk Park

Park, Chan Suk [s.n.] 1981 국내박사

미얀마에서 한류 드라마가 한국 국가 이미지 및 제품 구매의도에 미치는 영향 연구

AUNG KHIN CHAN MYAE 경희대학교 대학원 2019 국내석사

Abstract The Impect on Country Image and Purchase Intention Caused by Korean Wave in Myanmar - Mainly Focus on Korea Drama - Khin Chan Myae Aung Department of International Trade Graduate School of Kyung Hee University The purpose of this study is to investigate the effects of Korean dramas on Korean images, distance from Koreans, evaluations of Korean products and purchase intention of Korean products in Myanmar market. To achieve the study purpose, surveys were conducted on Yangon citizens in Myanmar. The result of this study can be summarized as follows: According to the results of the verification analysis, first, the Korean Wave has an important influence on the image of Korea. Secondly, both of Korea's National Image and Korea’s product image have a certain influence on Korean Product Purchase Intention. Thirdly, the Korea Drama also showed the significant influence on purchase intention as well. Depending on the subjectivity of survey respondents, the measurement of variables may not be entirely objective. It is also possible that the respondent did not understand the clear meaning between the measurement factors. Future research is needed to reflect more objective data. The presented research model and statistical results will be useful as a reference for export marketing studies.