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Title Page

Contents

LIST OF ABBREVIATIONS 10

ABSTRACT 12

CHAPTER 1. INTRODUCTION 14

1.1. Energy storage devices 14

1.2. History and classification of supercapacitors 16

1.2.1. Double-Layer Capacitors 18

1.2.2. Pseudocapacitors 19

1.2.3. Hybrid supercapacitors 21

1.3. Electrode materials 21

1.3.1. Carbon-based electrode materials 22

1.3.2. Conducting polymers 26

1.3.3. Transition metal compounds 27

1.4. Electrolyte 30

1.4.1. Liquid electrolytes 31

1.4.2. Organic electrolytes 32

1.4.3. Solid-state electrolytes 33

1.5. Objectives and outlines of research 36

CHAPTER 2. EXPERIMENTAL 39

2.1. Preparation of FexCo3-x DH precursors[이미지참조] 39

2.2. Structural conversion of FexCo3-xS4 NAs (positive electrode)[이미지참조] 40

2.3. Synthesis of ZIF-67 derived porous carbon (negative electrode) 40

2.4. Characterization techniques 41

2.5. Electrochemical measurement of as-synthesized electrodes. 42

2.6. Device fabrication and electrochemical performance 43

CHAPTER 3. RESULTS AND DISCUSSION 45

3.1. Characterization techniques and analysis for as-prepared electrodes 45

3.2. Electrochemical performance of as-prepared electrodes 55

3.3. Fabrication and electrochemical performance of the solid-state ASC devices 68

CONCLUSIONS 80

REFERENCES 81

국문초록 90

List of Tables

Table 3.1. Cyclic stability compared with the reported literature. 63

Table 3.2. Comparison of ASC device properties with reported literature. 75

List of Figures

Figure 1.1. Classification of supercapacitors based on the mechanism of charge storage. 18

Figure 1.2. Schematic and mechanism of Electric Double layer capacitors. 20

Figure 1.3. Schematic preparation of SPE membranes. 34

Figure 1.4. Schematic protocol of gel polymer electrolyte. 35

Figure 3.1. (a) Schematic of the rational design and fabrication of FeCo₂S₄ NAs on Ni foam for solid-state ASC application, (b) Low, (c) high magnification FE-SEM... 46

Figure 3.2. FESEM image of alternative electrode (a) FeCo₂ LDH (b) Co₃S₄ (c) Fe1.5 Co1.5S4 and (d) Fe0.75Co2.25S4[이미지참조] 47

Figure 3.3. The elemental composition of FeCo₂S₄. IN EDAX image Co, Fe, S and O were presented in FeCo₂S₄ 48

Figure 3.4. EDAX color mapping image Co, Fe, and S were presented in FeCo₂S₄. 49

Figure 3.5. (a) TEM image of the FeCo₂S₄ NAs (Inset shows the corresponding SAED pattern), (b) HR-TEM image of the FeCo₂S₄ NAs (Inset shows the corresponding... 51

Figure 3.6. (a) XRD pattern FexCo₃-xS₄, (b) Full XPS spectra, High resolution XPS spectra of (c) Fe 2p, (d) Co 2p, (e) S 2p, and (f) N₂ sorption isotherms of the... 53

Figure 3.7. Electrochemical performance of the FeCo₂S₄ NAs electrode: (a) CV curve with different sweep rates from 5 to 100 ㎷ s-1, (b) CV curves of the FexCo3-xS4...[이미지참조] 56

Figure 3.8. GCD curve with various scan rate (a) Co₃S₄ (b) Fe1.5Co1.5S4, (c) Fe0.75Co2.25S4 and (d) GCD curve of as synthesized electrodes at Current density of 5...[이미지참조] 58

Figure 3.9. Areal capacity vs. current density of FeCo₂S₄, Fe0.75Co2.25S4, Fe1.5Co1.5S4, and Co₃S₄ electrodes.[이미지참조] 61

Figure 3.10. Cyclic stability of FeCo₂S₄, Fe0.75Co2.25S4, Fe1.5Co1.5S4 and Co₃S₄ electrodes.[이미지참조] 64

Figure 3.11. (a) low and (b) high magnification SEM image of FeCo₂S₄ electrode (after 10,000 cyclic test). 64

Figure 3.12. Schematic illustration of organic framework derived porous carbon (MOF-PC) electrode. 66

Figure 3.13. (a) Low and (b) High magnification image (inset SAED pattern) of MOF-PC electrode. 67

Figure 3.14. CV curves at different scan rate from 5 ㎷ s-1 to 100 ㎷ s-1 of MOF-PC electrode.[이미지참조] 67

Figure 3.15. GCD curves at different current densities from 1 ㎃ ㎝-2 to 50 ㎃ ㎝-2 of MOF-PC electrode.[이미지참조] 68

Figure 3.16. Schematic representation of assembled solid state FeCo₂S₄ NAs//MOF-PC ASC device. 70

Figure 3.17. FeCo₂S₄ NAs and MOF-PC measures at the scan rate of 50 ㎷ s-1 in three- electrode system.[이미지참조] 71

Figure 3.18. Electrochemical performance of the solid-state FeCo₂S₄ NAs//MOF PC ASC device: (a) CV curve of the solid-state ASC with different operating voltage... 72

Figure 3.19. Different potential GCD curves of FeCo₂S₄ NAs//MOF-PC ASC device at current density at 5 ㎃ ㎝-2.[이미지참조] 73

Figure 3.20. GCD curves of FeCo₂S₄ NAs//MOF-PC ASC from 1st to 10th cycles.[이미지참조] 76

Figure 3.21. EIS of FeCo₂S₄ NAs//MOF-PC ASC during stability test. 76

Figure 3.22. Ragone plots of solid-state FeCo₂S₄ NAs//MOF-PC ASC device. 78

초록보기

 높은 표면적, 독특한 기공 구조, 많은 활성 부분을 가지고 있는 계층적 나노구조는 슈퍼캐퍼시터 전극 재료로 많은 각광을 받고있다.

본 연구에서는 슈퍼캐퍼시터의 에너지 밀도를 증가시키기 위해서, Fe: Co의 화학적 비율의 조절을 통한, 조정이 가능한 구조와 형태를 가지는 철 코발트 황화물을 설계하여 제조하는 새로운 방법을 제시 하였다. 최적 화학적 비율을 가지는 철 코발트는 전기전도도, 화학적 활성을 향상시켜, 매우 높은 비용량(~372.4 mAh g-1@ 1 mA cm-2)과 매우 우수한 셀 안정성(~97.8%, 10,000회 후)을 보였다. FeCo₂S₄ 와 음극으로는 금속유기골적구조기반 다공성 탄소를 사용하여, 고체 상태의 비대칭 슈퍼캐퍼시터를 제조 하였다. 높은 작동 전압(~1.6 V)을 보였으며, 전력밀도 0.73 kW kg-1에서 81.3W h kg-1의 매우 높은 에너지 밀도를 나타내었고, 탁월한 사이클 안정성(10,000회 후 5.8% 감소) 을 보였다. 높은 에너지 밀도와 전력 밀도를 보인 FeCo₂S₄가 미래 에너지 저장 기술을 위한 전극으로써 가능성을 보였다.