그래핀 기반 코어쉘 구조의 재료 및 투명전극의 제조에 관한 연구

다국어 초록 (Multilingual Abstract)

This study has two main objectives: preparation of a new anode material by hybridizing graphene with silicon, improving the charge capacity of a secondary battery, and application of the graphene in a transparent electrode and a display industry.
There are 5 chapters. Chapter 1 describes physical properties, a manufacturing method and applications of graphene. Also it introduces the current technological trend of anode materials for a secondary battery and deals with the materials and the manufacturing method of transparent electrode for ITO replacement.
Chapter 2 describes the study on the manufacture of silicon encapsulated with graphene (Si-GB) using polystyrene. Concerning application of graphene, a lot of efforts have been made to improve performance of nanomaterials in many fields, such as electric and electronic devices. Some examples are preparation of 3-dimension structured nanomaterials like nanoballs by CVD process and hybridizing with silicon. These graphene-based materials are proven to be available for secondary battery, EMI and ACF in electronics. Especially, some research has shown that they were very effective to enhance safety and volumetric capacity when they were used as anode materials of secondary battery. Although graphite and its compound with metal have been used as an anode material due to their high stability and reversibility, it still has lower charge capacity. On the contrary, silicon is known as a material which increases the charge capacity up to four times, compared with carbon-based materials, but it has lower stability and reversibility. For that reason, a few researchers just started to improve the charge capacity by hybridization of carbon-based material with silicon. In this paper, we prepared nanocarbon based material which has a new structure of graphene encapsulated silicon nanoball as an anode material which is applicable to high-capacity secondary battery. In order to form a graphene encapsulated silicon nanoballs, the polystyrene encapsulated silicon nanoballs were prepared by emulsion polymerization of styrene monomer with silicon nanoparticles. The resulting nanoballs were immersed in iron chloride solution and then dried. Finally they were treated in high temperature through CVD and etched by hydrogen chloride. Morphology of the graphene encapsulated silicon nanoballs was observed by the field emission scanning electron microscope (FESEM) and the field emission transmission electron microscope (FETEM) to search for core-shell structured nanoball. Spherical structure of graphene encapsulated silicon nanoball was investigated by the Raman, the X-ray Photoelectron Spectroscopy to identify graphene layers on the surface of the inner silicon core.
Chapter 3 details preparation of silicon nanoball encapsulated with a graphene shell. We carried out preparing silicon-graphene hybrid material. As the silicon tends to expand in volume, we intended to put some empty space between a grephene shell and a silicon ball, so that grephene shell can be protected. We intended to make the graphene vertically grow from inner silicon core. In order to form a core/shell structured graphene encapsulated silicon nanoball, nickel was coated on the surface of a silicon nanoball by an electroless plating method. Then, a graphene layer was synthesized on the surface of the nickel shell by a CVD process. We were able to make Si-GBs and Si-GFs by etching the nickel layer. The Si-GF was a particle including a vertically grown graphene from inner silicon core. The Si-GBs and Si-GFs were formed with a spherical void between the silicon particle and the graphene layer, which increases the safety against to volumetric change of anode during lithiation/delitiation of repeated charging-discharging in secondary battery cycles. Morphology of the graphene encapsulated silicon nanoball was observed by the field emission transmission electron microscope (FETEM) to find core-shell structured nanoball. Spherical structure of graphene encapsulated silicon nanoball was investigated by the Raman, the X-ray Photoelectron Spectroscopy to identify graphene layer on the surface of the inner silicon core.
Chapter 4 describes applications of grephene in the transparent electrode and flexible transparent electrode for display. Large-scale transparent conducting electrodes were fabricated using the electrospray method on a glass wafer and polyethylene terephthalate film using chemically reduced graphene oxide and poly (3,4-ethylene dioxy thiophene) (PEDOT). Graphene oxide (GO) is prepared by the modified Hummers method, and reduced GO (RG) is prepared at low temperature. By varying the concentration of RG and PEDOT of the composite material on the substrate, the electrical conductivity and transmittance of the electrode was controlled. The optical transmittance values of the graphene-based electrode at a wavelength of 550 nm were between 81 and 95 % and had sheet resistances from 370 to 5400 Ωsq-1. After 1000 cycles of a bending test, the sheet resistances of the graphene-based composite films were unchanged. Different types of graphene and graphene-based electrodes were characterized by field-emission scanning electron microscopy, high-resolution transmission electron microscopy, high resolution Raman spectroscopy, x-ray photoelectron spectroscopy, x-ray diffraction, transmittance, and electrical conductivity measurements.
Chapter 5 summarizes the conclusions that each chapter investigated were investigated in each chapter.

목차 (Table of Contents)

• Contents
• Contents 1
• List of Figures 5
• List of Tables 13
• Abstract 14
• Chapter 1.
• Literature Review 19
• 1.1 Description of Graphene 19
• 1.2 Physical Properties of Graphene 24
• 1.3 Preparation Methods of Graphene 30
• 1.3.1 Mechanical Exfoliation 30
• 1.3.2 Chemical Exfoliation 34
• 1.3.3 Chemical Vapor Deposition 37
• 1.3.4 Epitaxial Growth 42
• 1.4 Applications of Graphene 45
• 1.5 Secondary Battery and Anode material 53
• 1.6 Transparent Electrode 61
• 1.7 References 67
• Chapter 2.
• Preparation of Graphene Encapsulated Silicon Nanoball 74
• 2.1 Introduction 76
• 2.2 Experimental 78
• 2.2.1. Preparation of Graphene Encapsulated Silicon Nanoball 78
• 2.2.2. Characterizations 79
• 2.3 Results and Discussions 81
• 2.4 Conclusions 88
• 2.5 References 89
• Chapter 3.
• Preparation of Silicon Nanoball Encapsulated with Graphene Shell by CVD and Electroless Plating Process 92
• 3.1 Introduction 94
• 3.2 Experimental 98
• 3.2.1. Preparation of Silicon Encapsulated with Graphene shell 98
• 3.2.2. Characterizations 100
• 3.3 Results and Discussions 103
• 3.4 Conclusions 118
• 3.5 References 119
• Chapter 4.
• Large-Scale Graphene-Based Composite Films for Flexible Transparent Electrodes Fabricated by Electrospray Deposition 121
• 4.1 Introduction 123
• 4.2 Experimental 125
• 4.2.1 Preparation of Graphene 125
• 4.2.2 Fabrication of TCF 126
• 4.2.3 Characterization 129
• 4.3 Results and Discussion 130
• 4.4 Conclusions 143
• 4.5 References 144
• Chapter 5
• Conclusions 148
• 국문초록 152
• 감사의 글 156

참고문헌 (Reference)

1. 전기화학, 오승모, 자유아카데미, 자유아카데미, , 2010