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Title Page

Contents

Abstract 12

1. Introduction 13

1.1. Necessity of anode materials due to the appearance of sodium ion batteries as the next generation batteries 13

1.2. Comparing CONs and COFs with suitability as an anode material. 14

1.3. Strategy to increase electron density in SIB through fluorination at backbone of CONs 16

1.4. Approximate appearance of chemically engineering of CON-35 and CON-37 with stille cross-coupling method and reason for fluorination site. 19

2. Experimental 21

2.1. Materials & instruments 21

2.2. Preparation of CON-35 22

2.3. Preparation of CON-37 23

2.4. Half-cell assembly and electrochemical measurements 25

3. Results and Discussion 27

4. Conclusion 98

5. References 100

Published paper 104

List of Tables

Table 1. XPS elemental profile of CON-35 45

Table 2. XPS elemental profile of CON-37 45

Table 3. Impedance data were result from equivalent circuit model (ECM) in Fig. 31 and 32 80

Table 4. Comparing sodium storage efficiency of organic and carbon based anodes when fluorine was utilized at electrode materials. 95

List of Figures

Fig. 1. FT-IR spectrum of CON-35 and CON-37 using ATR transmittance mode 28

Fig. 2. UV-Vis spectroscopy of CON-35 and CON-37 using Kubelka-Munk mode 28

Fig. 3. Mulliken atomic charge distribution of (a) CON-37 and (b) CON-35 calculated using density function theory (DFT) at B3LPY/6-31G level. (c) DFT calculation results... 31

Fig. 4. Solid ¹³C CP/MAS NMR spectrum of CON-35 and CON-37 33

Fig. 5. Structure of CONs indicating the carbon position according to carbon NMR spectrum 33

Fig. 6. PXRD peaks of CON-35 and CON-37. 36

Fig. 7. BET plot using N₂ gas adsorption and desorption of CON-35 (red) and CON-37 (green) 36

Fig. 8. (a) CON-35 and (b) CON-37 images of FE-SEM 38

Fig. 9. FE-TEM images of (a),(b) CON-35 and (d),(e) CON-37 41

Fig. 10. Brightness data from the selected area of rectangle at Fig.9b and Fig. 9e (CON-35 for red, CON-37 for green box) 41

Fig. 11. (a) XPS spectrum of CON-35 and enlarged spectra of (b) C₁ₛ (c) S₂ₚ (d) N₁ₛ (e) Sn₃d and (f) O₁ₛ[이미지참조] 44

Fig. 12. (a) XPS spectrum of CON-35 and enlarged spectra of (b) C₁ₛ (c) S₂ₚ (d) N₁ₛ (e) Sn₃d and (f) O₁ₛ[이미지참조] 44

Fig. 13. XANES (X-ray absorption near edge structure) analysis for CON-35 and CON-37 45

Fig. 14. Cyclic voltammogram of CON-37 47

Fig. 15. Cyclic voltammogram of CON-35 47

Fig. 16. CV profile with different scan rate of CON-37 50

Fig. 17. CV profile with different scan rate of CON-35 50

Fig. 18. Cottrell plot of CON-37 51

Fig. 19. Cottrell plot of CON-37 51

Fig. 20. B-value profile by comparing CON-37 and CON-35 at different voltages. 52

Fig. 21. Pseudocapacitive and diffusion-controlled charge storage process separative profile of CON-37 55

Fig. 22. Pseudocapacitive and diffusion-controlled charge storage process separative profile of CON-35 55

Fig. 23. Ratio of pseudocapacitive contribution and diffusion-controlled process of CON-37 and CON-35 (gray position refer to diffusion-controlled process). 56

Fig. 24. Illustrate of binding of sodium on CON electrode. (a) refer to CON-35 and (b) refer to CON-37 and blue ball refer to sodium ion 56

Fig. 25. dQ/dV curve of CON-37 63

Fig. 26. dQ/dV curve of CON-35 63

Fig. 27. Nyquist plot of the CON-37 measuring during the initial second cycle 64

Fig. 28. Nyquist plot of the CON-37 measuring during the initial second cycle 64

Fig. 29. Bode plot of CON-37 electrode during first cycle 65

Fig. 30. bode plot of CON-37 electrode during first cycle 65

Fig. 31. EIS data by ECM of CON-37 electrode before the initial cycle 70

Fig. 32. EIS data by ECM of CON-37 electrode after initial discharge process 70

Fig. 33. DRT plot of CON-37 71

Fig. 34. DRT plot of CON-35 71

Fig. 35. ECM fits of CON-35 and CON-37 by comparing of ECM parameters 72

Fig. 36. Warburg coefficient of CON-35 and CON-37 72

Fig. 37. Kramers-Kronig relative residual profile of CON-37 (a,d) and CON-35 (b,e) 73

Fig. 38. Nyquist plot of CON-37 up to 1000th cycle[이미지참조] 77

Fig. 39. Nyqsuit plot of CON-35 up to 1000th cycle[이미지참조] 77

Fig. 40. DRT plot of CON-37 up to 1000th cycle[이미지참조] 78

Fig. 41. DRT plot of CON-35 up to 1000th cycle[이미지참조] 78

Fig. 42. ECM fits of CON-35 and CON-37 by comparing of ECM parameters up to 1000th cycle[이미지참조] 79

Fig. 43. Warburg coefficient of CON-35 and CON-37 up to 1000th cycle[이미지참조] 79

Fig. 44. Ex-situ FT-IR spectrum of CON-35 (a,b) 82

Fig. 45. Rate performance of CON-35 and CON-37 by using different current density (100~1000 mA/g) 86

Fig. 46. Charge discharge profiles of CON-37 with different current density (100~1000 mA/g) 86

Fig. 47. Charge discharge profiles of CON-35 with different current density (100~1000 mA/g) 87

Fig. 48. CON-37 and CON-35 rate performance measuring at 100~1000 mA/g 87

Fig. 49. (a),(b) is charge and discharge profiles of CON-37 and (c),(d) is CON-35 88

Fig. 50. Capacity performance of CON-35 and CON-37 by using different current density at 300 mA/g 93

Fig. 51. Charge discharge profiles of CON-37 with different current density at 300 mA/g 93

Fig. 52. Charge discharge profiles of CON-35 with different current density at 300 mA/g 94

Fig. 53. dQ/dV curves of (a) CON-37 and (b) CON-35 with different charge and discharge cycle. (c), (d) comparing of polarization when current density varies. 94

Fig. 54. TEM images of CON-37 and (a ~ g) EDS elemental distribution mapping images at same distriction after 2500 charge and discharge cycle. (h), (i) refer to... 97

List of Schemes

Scheme 1. synthetic mechanism and structure of CON-35, CON-37 24

초록보기

 In this research, the performance linked to the structural attributes of covalent organic nanosheets (CONs) when employed as anode components in sodium-ion batteries has been thoroughly scrutinized by introducing an electron withdrawing group, such as fluorine, into the foundational CON structure. Subsequently, permanent dipoles which is occurred by fluorine are effectively retained within the CON framework, rendering an abundance of accessible locations for Na+ ions within the self-assembled matrices. The influence of fluorine was confirmed by comparing fluorinated CONs (CON-37) with no fluorinated CONs (CON-35). Because fluorine has the ability to reduce the electron density within the framework, Na+ show low affinities with framework of CON-37 than CON-35. Because of this properties, CON-37 shows high electron density and cycling stability. The CON-37 electrode demonstrates a consistent cycling performance and rate capability, sustaining a significantly enhanced reversible discharge capacity.

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