Title Page
ABSTRACT
국문 초록
Contents
CHAPTER 1. INTRODUCTION 14
1.1. Introduction 14
1.2. Previous studies on CoF₂ as a cathode of LIBs 19
CHAPTER 2. CONVERSION REACTION KINETICS ENHANCEMENT THROUGH NANOSTRUCTURING OF CoF₂ WITH CONDUCTIVE MWCNTS 21
2.1. Introduction 21
2.2. Experimental 23
2.2.1. Materials preparation 23
2.2.2. Materials characterization 25
2.2.3. Electrochemical characterization 26
2.3. Results and discussion 27
2.3.1. Synthetic mechanisms and structure analysis 27
2.3.2. Electrochemical performance 40
2.4. Summary 47
CHAPTER 3. THE STATEGIES TO MITIGATE CAPACITY LOSS OF CoF₂/MWCNTS 48
3.1. Introduction 48
3.2. Electrolyte modification to reduce capacity degradation 50
3.2.1. Experimental 50
3.2.2. Results and discussion 51
3.3. Atomic layer deposition (ALD) coating to prevent capacity fading 57
3.3.1. Experimental 57
3.3.2. Results and discussion 58
3.4. Summary 67
CHAPTER 4. CONCLUSION 68
REFERENCES 70
Figure 1-1. (a) Theoretical gravimetric and (b) volumetric capacities with theoretical working potential of selected halogens and metal halides. 17
Figure 1-2. General strategies for enhancement of the performance of cells comprising conversion-type cathode materials: (a) optimization of the architecture,... 18
Figure 2-1. Schematics of CoF₂/MWCNTs nanocomposites fabrication. 24
Figure 2-2. XRD patterns of bare cobalt precursor, bare CoF₂, cobalt precursor/MWCNTs and CoF₂ MWCNTs. 28
Figure 2-3. Crystalline phase change of CoF₂/MWCNTs during heat treatment with NH₄F. 30
Figure 2-4. Reaction mechanism of NH₄F-mediated synthesis of CoF₂. 31
Figure 2-5. SEM, TEM images of bare cobalt precursor and bare CoF₂. 33
Figure 2-6. SEM, TEM images of cobalt precursor/MWCNTs and CoF₂/MWCNTs. 34
Figure 2-7. (a) STEM image of CoF₂/MWCNTs. (b-d) EDS elemental mapping of (b) carbon, (c) cobalt and (d) fluorine. 35
Figure 2-8. XPS analysis of CoF₂/MWCNTs nanocomposites. (a-c) High resolution XPS of (a) C 1s, (b) Co 2p and (c) F 1s. 37
Figure 2-9. TGA of CoF₂/MWCNTs nanocomposites. 39
Figure 2-10. Electrochemical performance of bare CoF₂ and CoF₂/MWCNTs. CV graph scanned between 1.0 and 4.0 V vs. Li/Li+ at a scan rate of 0.1 mV s−1 of (a)...[이미지참조] 42
Figure 2-11. (a, b) Cycle properties of (a) bare CoF₂ and CoF₂/MWCNTs and (b) pure MWCNTs. (c, d) Voltage profiles of (c) bare CoF₂ and (d) CoF₂/MWCNTs at... 44
Figure 2-12. (a) Electrochemical impedance spectroscopy (EIS) spectra of bare CoF₂ and CoF₂/MWCNTs, (b) the equivalent circuit model, (c) GITT curves and (d) internal resistance... 46
Figure 3-1. Voltage profiles of (a) CoF₂/MWCNTs at the first cycle with various C-rates (0.1 C, 0.2 C, 0.5 C, 1 C and 2 C) and (b) pure MWCNTs. Cycle performance... 53
Figure 3-2. Post-mortem analysis of separator after 100th cycle in EC/DMC electrolyte: (a) SEM image and (b-d) EDS elemental mapping of (b) cobalt, (c)... 55
Figure 3-3. Post-mortem analysis of separator after 100th cycle in FEC/EMC electrolyte: (a) SEM image and (b-d) EDS elemental mapping of (b) cobalt, (c)...[이미지참조] 56
Figure 3-4. XPS spectrum of Al 2p for (a) 20A-CoF₂/MWCNTs and (b) 50A-CoF₂/MWCNTs. 59
Figure 3-5. (a) STEM image of 50A-CoF₂/MWCNTs. (b-d) EDS elemental mapping of (b) aluminum, (c) cobalt and (d) fluorine. 60
Figure 3-6. (a) Cycling performance and (b) electrochemical impedance spectroscopy (EIS) spectra of CoF₂/MWCNTs, 20A-CoF₂/MWCNTs and 50A-... 63
Figure 3-7. Long-term cycle stability of 20A-CoF₂/MWCNTs and 50A-CoF₂/MWCNTs at 0.2 C. 64
Figure 3-8. Post-mortem analysis of separator of 50A-CoF₂/MWCNTs after 500th cycle in FEC/EMC electrolyte: (a) SEM image and (b-d) EDS elemental mapping of...[이미지참조] 66