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Title Page

초록

Abstract

Contents

Chapter 1. Introduction 11

1.1. Overview of issues on rechargeable battery 11

1.2. Lithium-Sulfur batteries: The next-generation secondary batteries 12

1.3. Research trend of Lithium-Sulfur batteries 14

1.4. Ph. D thesis: Theoretical background and objectives 16

1.5. References 18

Chapter 2. Covalent Triazine Frameworks Incorporating Charged Polypyrrole Channels for High Performance Lithium-Sulfur Batteries 20

2.1. Research Background 20

2.2. Experimental Section 22

2.3. Results and Discussion 25

2.4. Conclusion 43

2.5. References 44

Chapter 3. Cobalt(Ⅱ)-Centered Fluorinated Phthalocyanine-Sulfur SNAr Chemistry for Robust Lithium-Sulfur Batteries with Superior Conversion Kinetics[이미지참조] 48

3.1. Research Background. 48

3.2. Experimental Section 50

3.3. Results and Discussion 53

3.4. Conclusion 65

3.5. References 66

Chapter 4. Concluding Remark 72

Chapter 2. 27

Table 2-1. ID/IG values calculated from Raman spectroscopy of various cPpy-S-CTFs.[이미지참조] 27

Table 2-2. EIS results of cPpy-S-CTF 0, 1, 2.5, 5, and 10% before cycling, after 100 cycles of full charge and discharge. 41

Chapter 1. 11

Figure 1-1. Application of rechargeable batteries for renewable energy sources and energy density and power density of secondary batteries. 11

Figure 1-2. Schematic and reaction mechanisms of Li-S battery and energy density potential of various types of rechargeable batteries. 13

Figure 1-3. Schematic illustration of polysulfides shuttle reaction mechanisms and detailed discharge plateau of sulfur utilization. 14

Figure 1-4. Representative researches for utilize sulfur with physical confinement to mitigate inherent problems of sulfur as cathode material. 15

Figure 1-5. Representative researches for utilize sulfur with chemical confinement to mitigate inherent problems of sulfur as cathode material. 15

Chapter 2. 25

Figure 2-1. Synthetic scheme for the elemental sulfur-mediated synthesis of cPpy-S-CTFs incorporating different amounts of cPpy via SNAr chemistry and inverse vulcanization.[이미지참조] 25

Figure 2-2. Structural analysis of various cPpy-S-CTFs. (a) FT-IR spectra. (b) Raman spectra. (c) TGA curves obtained under N₂ atmosphere. TEM images of (d) cPpy-S-CTF 0% cPpy and (e) cPpy-S-CTF 2.5% cPpy.... 26

Figure 2-3. XRD spectra of elemental sulfur, cPpy-S-CTF 0%, cPpy-S-CTF 1%, cPpy-S-CTF 2.5%, cPpy-S-CTF 5%, and cPpy-S-CTF 10%. 28

Figure 2-4. C 1s XPS profiles of (a) cPpy-S-CTF 0%, (b) cPpy-S-CTF 1% (c) cPpy-S-CTF 2.5%, (d) cPpy-S-CTF 5%, (e) cPpy-S-CTF 10%, and (f) cPpy. 29

Figure 2-5. N 1s XPS profiles of (a) cPpy-S-CTF 0%, (b) cPpy-S-CTF 1% (c) cPpy-S-CTF 2.5%, (d) cPpy-S-CTF 5%, (e) cPpy-S-CTF 10%, and (f) cPpy. 30

Figure 2-6. SEM images of various cPpy-S-CTFs. (a) cPpy-S-CTF 0%. (b) cPpy-S-CTF 1%. (c) cPpy-S-CTF 2.5%. (d) cPpy-S-CTF 5%. (e) cPpy-S-CTF 10%. (f) cPpy only. 32

Figure 2-7. NLDFT pore size distributions of various cPpy-CTFs using standard carbon slit model. 33

Figure 2-8. Visual effects of the 3 mM Li₂S₆ in DOL/DME (1:1 v/v) solution when exposed to various cPpy-CTFs over 3, 6 and 24 h (a, b, c). Time dependent UV-Vis absorption spectra of cPpy-CTF 0 (d), 2.5 (e), and 10%... 34

Figure 2-9. Electrochemical performance of various cPpy-S-CTFs. (a) Comparison of the first discharge-charge profiles of cPpy-S-CTFs at 0.05C in the potential range 1.8-2.7 V (1C＝1675 mA g⁻¹). (b) Rate performance of... 35

Figure 2-10. (a) Cycling performance and coulombic efficiencies of cPpy-S-CTFs at 1C and 0.8 mgsulfur cm⁻² for 500 cycles. (b) Cycling performance and Coulombic efficiencies of cPpy-S-CTFs at 2C and 0.8 mgsulfur cm⁻² for...[이미지참조] 36

Figure 2-11. CV plots of (a) cPpy-S-CTF 0%, (b) cPpy-S-CTF 2.5%, and (c) cPpy-S-CTF 5% in the potential range 1.8-2.7 V at various scan rates (0.05-0.5 mV s⁻¹). Plots of CV peak current vs. the square root of scan rate... 38

Figure 2-12. Nyquist plots of cPpy-S-CTFs (0-10%). (a) Before cycling, (b) after 100th charge, and (c) after 100th discharge.[이미지참조] 40

Chapter 3. 53

Figure 3-1. Schematic illustration of the integration of rGO with F-Co(Ⅱ)Pc and subsequent covalent attachment of elemental sulfur via an SNAr reaction.[이미지참조] 53

Figure 3-2. (a) UV-vis absorption spectra of F-Co(Ⅱ)Pc with rGO in ethanol. Photographs of F-Co(Ⅱ)Pc in ethanol when exposed to rGO for (b) 0 and (c) 30 min. 54

Figure 3-3. FE-SEM images and energy-dispersive X-ray spectroscopy (EDAX) elemental mapping results of G-Co(Ⅱ)Pc (a-d) before and (e-h) after the SNAr reaction. (i) F 1s XPS profiles of F-Co(Ⅱ)Pc and SG-Co(Ⅱ)Pc. (j)...[이미지참조] 56

Figure 4-4. (a) Digital photographs showing the adsorption capability of different samples targeting 3 mM Li₂S₆ in DOL/DME (1:1, v/v) solution. (b) UV-vis adsorption spectra of Li₂S₆ solution with different samples. (c) CV... 57

Figure 3-5. Electrochemical performance of SG-Co(Ⅱ)Pc and S-rGO composite electrodes in the voltage range 1.8-2.7 V. (a) Cycling performance of SG-Co(Ⅱ)Pc and S-rGO composite electrodes with areal sulfur loading of... 59

Figure 3-6. (a) Cycling performance of SG-Co(Ⅱ)Pc and S-rGO composite electrodes with areal sulfur loading of 12 mgsulfur cm⁻² when measured at 0.2C. (b) Discharge-charge curves of SG-Co(Ⅱ)Pc and S-rGO composite...[이미지참조] 62

초록보기

 현재 상용화되어있는 리튬 이온전지의 명확한 한계인 낮은 에너지밀도와 비용량 문제를 해결하기 위해 전세계적으로 많은 연구가 진행되고 있다. 차세대 이차 전지 중 가장 현실적이라고 평가받고 있는 리튬 - 유황 이차전지는 가격이 싸고 높은 에너지밀도 및 비용량을 가지고 있지만, 폴리설파이드 용해로 인한 수명 특성 감소와 전기적 부도체라는 근본적인 한계를 가지고있다. 따라서, 본 논문은 낮은 전도도 및 리튬 폴리설파이드 용출을 해결하기 위한 한 가지 화학적 접근법을 소개한다. 이는 '친핵성 방향족 치환' 합성법으로써 불소 작용기가 포함된 방향족 골격에 유황을 치환시키는 방법이다. 이 방법은 높은 반응 수율을 얻을 수 있음과 동시에 방향족 분자에 존재하는 다양한 헤테로 원자와 금속으로 인하여 전도성 및 리튬 폴리설파이드 흡착력을 구현한다. 본 학위논문에서는 유황을 불소화된 방향족 분자와 친핵성 방향족 치환법을 통해 얻은 복합체를 리튬 이온과의 전기화학 반응 메커니즘과 그에 따르는 리튬 폴리설파이드 용출 제어방법을 다루고자 한다.

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