Title Page
Contents
ABSTRACT 12
Chapter 1. Introduction 14
1.1. Li-ion batteries (LIBs) 14
1.2. 2D-based layered materials for LIBs 16
1.2.1. Cathode 16
1.2.2. Anode 17
1.3. Anisotropic properties and challenges 22
1.4. Objectives 24
Chapter 2. Edge-enrichment of graphene oxide by the control of oxidation degree 25
2.1. Introduction 25
2.2. Experimental 27
2.2.1. GO preparation 27
2.2.2. The heat treatment of GO 27
2.2.3. Material characterization 27
2.2.4. Electrochemical measurements 28
2.3. Results and discussion 29
2.4. Summary 39
Chapter 3. The increase of lithium-active edge component 40
3.1. Introduction 40
3.2. Experimental 43
3.2.1. (NH₄)₂Mo₃S₁₃·xH₂O preparation 43
3.2.2. Thermal treatment of (NH₄)₂Mo₃S₁₃·xH₂O 43
3.2.3. Material characterization 43
3.2.4. Electrochemical measurement 44
3.3. Results and discussion 45
3.4. Summary 64
Chapter 4. The coating of size-controlled polycyclic aromatic hydrocarbons on active materials by self-assembly 65
4.1. Introduction 65
4.2. Pitch-derived PAH coating for binding the sulfur enriched Mo₃S₁₃ clusters for enhanced electrochemical performances 69
4.2.1. Introduction 69
4.2.2. Experimental 72
4.2.3. Results and discussion 74
4.2.4. Summary 91
4.3. The heat treatment effect on pitch-derived carbon coating layer on the silicon nanoparticles for high performance Li-ion batteries 92
4.3.1. Introduction 92
4.3.2. Experimental 95
4.3.3. Results and discussion 97
4.3.4. Summary 117
Chapter 5. Conclusion and perspectives 118
References 120
Appendix 139
Abstract (in Korean) 140
Table 1. Summary of fitted parameters of EIS data in figure 3-8 54
Table 2. Summary of EIS parameters fitted based on the electric circuit exhibited in the inset of figure 4-8(d) 86
Table 3. Summary of BET surface area and pore volume of N₂ physisorption of Si Np and PCT/Si composites 109
Table 4. Summary of fitted impedance parameters. The Nyquist plots were fitted based on the electric circuit exhibited in the inset of figure 4-21(d). 114
Figure 1-1. The Ragone plot of batteries and supercapacitors 14
Figure 1-2. Schematic illustration of Li-ion battery system 16
Figure 1-3. a) a periodic table with colored elements for anode materials studies for fast charge/discharge of LIB, and (b) its structures 18
Figure 2-1. Illustration of the synthesis procedure for GOxx and aGOxx 29
Figure 2-2. AFM images of (a) GO15, (b) GO30, and (c) GO50, and the sheet size distribution of (d) GO15, (e) GO30, and (f) GO50. The size was... 30
Figure 2-3. XPS C1s spectra of (c) GO15, (b) GO30, and (c) GO50, and (d) the configuration of deconvoluted peaks of (a-c). The atomic percentage was... 32
Figure 2-4. XRD spectra of (a) GOxx and (b) aGOxx 32
Figure 2-5. XPS C1s spectra of (a) aGO15, (b) aGO30, and (c) aGO50, and (d) the configuration of deconvoluted peaks of (a-c) 34
Figure 2-6. Electrochemical test results of aGOxx. (a) The voltage profile at 0.1 A/g, (b) CV data performed with the scan rate of 0.2 mV/s, (c) rate performance... 36
Figure 2-7. a plot of the relationship between the average sheet size of GOxx and the b-value of aGOxx 38
Figure 2-8. EIS spectra of (a) GOxx and (b) aGOxx. The data was fitted based on the electric circuit shown in the inset of (a). 38
Figure 3-1. An illustration of transformation mechanism from amorphous MoS₃ to crystalline Mo₃S₁₃ clusters based on Weber's hypothesis 46
Figure 3-2. SEM image of (a) amorphous MoS₃, and(b) Mo₃S₁₃ clusters 48
Figure 3-3. (a) XRD spectra of amorphous MoS₃ and Mo₃S₁₃ clusters. XPS (b) S2p spectra and (c) Mo3d spectra of Mo₃S₁₃ clusters 48
Figure 3-4. images of electrode after coating on Cu foil. (a) Mo₃S₁₃-PVDF-NMP, (b) Mo₃S₁₃-PVDF-DMF, (c) Mo₃S₁₃-PAA-IPA, and (d) Mo₃S₁₃-PVDF-H₂O 50
Figure 3-5. XRD spectra of "Mo₃S₁₃-binder-solvent" 50
Figure 3-6. Electrochemical performances of Mo₃S₁₃-binder-solvent. CV of (a) Mo₃S₁₃-PAA-IPA, and of (b) Mo₃S₁₃-PVdF-NMP. The galvanostatic voltage profile... 53
Figure 3-7. Rate performance of (a) Mo₃S₁₃-binder-solvent and (b) Mo3S13 cluster compared with MoS₂ and MoS₃ 53
Figure 3-8. Nyquist plot of Mo₃S₁₃-binder-solvent. The electric circuit in the inset was used for fitting the data 55
Figure 3-9. Nyquist plots of Mo₃S₁₃-binder-solvent electrodes before and after cycling. (a) Mo₃S₁₃-PAA-IPA, (b) Mo₃S₁₃-PAA-H₂O, (c) Mo₃S₁₃-PVdF-DMF and... 55
Figure 3-10. Post-mortem FE-SEM images of Mo₃S₁₃-binder-solvent electrodes (a, c, e, g) before and (b, d, f, g) after 60 cycles 56
Figure 3-11. TGA thermograms of (NH₄)₂Mo₃S₁₃·xH₂O 58
Figure 3-12. (a) XRD spectra, (b) XPS S2p spectra, and (c) its plots of bonding configuration changes of bride/apical sulfur and terminal sulfur 58
Figure 3-13. Mechanism of chemical structural changes of Mo₃S₁₃ clusters during heat treatment 60
Figure 3-14. SEM images of Mo₃S₁₃-X after heat treatment at (a) 195°C, (b) 240°C, (c) 340°C, and (d) 450°C 61
Figure 3-15. Electrochemical performances of Mo₃S₁₃-X. The voltage profile of (a) first cycle and (b) third cycle, (c) rate performance at the current density from... 63
Figure 4-1. MALDI-TOF mass spectra of (a) the petroleum-based pitch and (b) PCT (inset is a magnified plot with m/z from 300 to 400) 75
Figure 4-2. (a) FT-IR spectrum and (b) XPS C1s narrow spectrum of PCT powder 77
Figure 4-3. (a) HR-TEM image and (b) in high magnification image of PCT 78
Figure 4-4. FE-SEM images of (a) as prepared Mo₃S₁₃ cluster, (b) Mo₃S₁₃-48h, and the electrode of (c) Mo₃S₁₃ cluster and (d) Mo₃S₁₃-48h 80
Figure 4-5. FE-SEM images of (a) Mo₃S₁₃-48h, (c) PCT/Mo₃S₁₃ (1:10), (e) PCT/Mo₃S₁₃ (1:5) and (g) PCT/Mo₃S₁₃ (1:1) and (b, d, f, h) its prepared electrodes 81
Figure 4-6. (a) HR-TEM image, (b) dark-field HR-TEM image, and elemental mapping images of (c) molybdenum, (d) sulfur, and (e) carbon of... 83
Figure 4-7. XPS (a) S2p spectra of Mo₃S₁₃-48h and PCT/Mo₃S₁₃ composites, and (b) C1s spectra of PCT and PCT/Mo₃S₁₃ composites 84
Figure 4-8. Electrochemical performances of Mo₃S₁₃-48h and PCT/Mo₃S₁₃ composites. (a) galvanostatic charge/discharge curve, (b) rate performances, (c)... 87
Figure 4-9. EIS spectra of electrodes before and after 200 cycles. (a) Mo₃S₁₃-48, (b) PCT, (c) PCT/Mo₃S₁₃ (1:10), (d) PCT/Mo₃S₁₃ (1:5), and (e) PCT/Mo₃S₁₃ (1:1) 89
Figure 4-10. FE-SEM images of Mo₃S₁₃-48h, PCT, and PCT/Mo₃S₁₃-based electrode before and after 200 cycles 90
Figure 4-11. TGA thermograms of (a) pristine pitch and PCT, and (b) PCT/Si Np-1 98
Figure 4-12. XRD spectra of PCT, PCT-700 and PCT-900. 100
Figure 4-13. FT-IR spectra of PCT before and after the heat treatment at 350°C, 700°C, and 900°C. 100
Figure 4-14. HR-TEM images of (a) PCT-350, (c) PCT-700, and (e) PCT-900 and (b, d, f) its high magnification images 102
Figure 4-15. FE-SEM images of (a) Si Np, (c) PCT/Si-1, (e) PCT/Si-1-350, (g) PCT/Si-1-700, (i) PCT/Si-1-900, and (b, d, f, h, j) its high magnification images 104
Figure 4-16. HR-TEM images of (a, b) Si Nps and (c, d) PCT/Si-1-700 106
Figure 4-17. HR-TEM elemental analysis of PCT/Si-1-700. (a) HR-TEM image, (b) Dark-field image, and elemental mapping images of (c) silicon, (d) carbon,... 107
Figure 4-18. N₂ adsorption/desorption isotherm plots of (a) Si Np and as prepared PCT/Si Np composites, and (b) PCT/Si Np composites before and after... 110
Figure 4-19. XRD spectra of Si Np and PCT/Si composites before and after the heat treatment 112
Figure 4-20. TGA curves of Si Np, PCT, and PCT/Si Np composites 112
Figure 4-21. (a) galvanostatic charge/discharge curves, (b) rate performances, (c) capacity retention plots of rate performances, and (d) Nyquist plots, (e)... 115