Title Page
ABSTRACT
국문 초록
Contents
CHAPTER 1. INTRODUCTION 13
CHAPTER 2. EXPERIMENTAL METHOD 17
2.1. Materials preparation 17
2.2. Preparation of the anodes and half-cells 18
2.3. Electrochemical tests 19
2.4. Material characterization 20
2.5. Interfacial interaction calculations 21
2.6. Adsorption energy calculations 22
2.7. Structure analyses 23
2.8. Diffusivity measurement of the intermediate phases 24
2.9. Resistivity calculations of the intermediate phases 25
CHAPTER 3. RESULTS AND DISCUSSION 26
3.1. Microstructural evolution of various metal sulfide particles 26
3.2. DFT interpretation of the coalescence behaviors 31
3.3. Electrochemical performance of the various MxS anodes[이미지참조] 36
3.4. Phase identification in the model half-cells 39
3.5. Electrochemical characteristics of the intermediate phases 43
3.6. Morphological changes of metal particles during cycling 48
CHAPTER 4. CONCLUSION 53
REFERENCES 54
Figure 1.1. Rate performance of the various metal sulfide anodes. (a) Variations in the capacity retention of the Na–NiS, Na–CuS, Na–MnS, Na–Bi₂S₃, Na–FeS₂, and Na–FeS half-... 16
Figure 3.1. Spontaneous transformation into a porous nanostructure. (a–e) Representative images recorded from the surfaces of the CuS particles extracted from the anodes subjected... 28
Figure 3.2. Secondary electron images recorded at (a) low and (b) high magnifications from the uncycled CuS anode, showing the surfaces of the CuS particles. 29
Figure 3.3. (a) Secondary electron image, showing the morphologies of microscale and (b) XRD of NiS nanoparticles. (c) Secondary electron image, showing the morphologies of... 30
Figure 3.4. Adsorption behaviors of the solvents on the CuS surface. DFT results, showing the movement of the (a) EC, (b) DEC, and (c) DME molecules relative to the CuS surface.... 33
Figure 3.5. Optimized structures of the CuS/electrolyte interfaces obtained from DFT calculations, revealing the interactions between CuS and the electrolyte components: (a) EC,... 34
Figure 3.6. (a) Atomic configurations and (b) charge density distributions and (c) electrostatic potential of solvent molecules (EC, DEC, and DME) and active material (CuS) optimized... 35
Figure 3.7. Electrochemical performances of Na–NiS, Na–CuS, and Na–MnS half-cells. (a) Changes in specific capacity of Na–NiS, Na–CuS, and Na–MnS half-cells measured at... 38
Figure 3.8. (a) Capacity–voltage curve obtained from the CuS anode after six cycles at 0.1C. (b) XRD spectra collected at different states of charge indicated in (a). (c) Atomic structures... 40
Figure 3.9. (a) Cyclic voltammetry curves of NiS anodes measured at various scan rates of Na– NiS half-cell with DME solvent measured at 0.1C (59 mA/g). (b) Cyclic voltammetry... 41
Figure 3.10. Phase transition sequence of the NiS, CuS, and MnS anodes. a–c) XRD spectra and capacity–voltage curve of the Na–NiS, Na–CuS, and Na–MnS half-cell recorded during... 42
Figure 3.11. Electronic conductivity of the intermediate phases. (a) DFT results, showing the electronic conductivity evaluated for various phases formed during sodiation in the Na–NiS,... 46
Figure 3.12. Band structures calculated for the Na₂S phase formed in the metal sulfide system during discharging (or sodiation). The inset image is the corresponding crystal structure. 47
Figure 3.13. TEM. a-c) Bright-field image and selected area diffraction pattern (the inset image) recorded from the Na₂S/M (Mn, Cu, and Ni) composite, showing the uniformly... 50
Figure 3.14. (a) Bright-field image of the Na₂S/Cu composite, showing the uniformly dispersed Cu nanoparticles (dark spots) embedded in the Na₂S matrix (grey background). (b)... 51
Figure 3.15. (a) High-resolution transmission electron microscopy image recorded from the Na₂S/Cu composite. The FFT patterns of the dashed red square in (a), showing the presence... 52