Chapter I. Introduction 9

Figure 1.1. Crystal structure of LiₓTiS₂ during Li⁺ intercalation. Reproduced with permission. 21

Figure 1.2. A schematic presentation of the discharging (a) and charging (b) processes in lithium-ion batteries. Reproduced with permission. 22

Figure 1.3. Crystal structure of olivine, layered and spinel-type. Reproduced with permission. 23

Figure 1.4. Theoretical gravimetric and volumetric capacities and theoretical potential of selected conversion cathode materials: (a, b) chalcogens and chalcogenides; (c, d) halogens and metal halides.... 25

Figure 1.5. Two types of conversion reactions using lithiation of S and FeF₂ as examples: (a) true conversion with the formation of two new phases; (b) chemical transformation with a single new phase... 28

Figure 1.6. Scheme of challenges of conversion-based cathode. Reproduced with permission. 31

Figure 1.7. Scheme of higher redox potential of Cu-P bond than that of Cu-O bond arising from inductive effect by sulfur with high electronegativity. Reproduced with permission. 34

Figure 1.8. Scheme of merits of carbon coating and nano-sizing. 38

Chapter 2. Development of Novel Cathode with Large Lithium Storage Mechanism Based on Pyrophosphate‐Based Conversion Reaction for Lithium-ion Batteries 9

Figure 2.1. Scheme of nano-sizing and carbon mixing of nano-C-CPO particles using high-energy ball milling 50

Figure 2.2. XRD patterns of nano-C-CPO composites which coated with different carbon content 51

Figure 2.3. Cycle-performances of nano-C-CPO composites which coated with different carbon content 52

Figure 2.4. Comparing XRD intensity between nano-C-CPO and pristine Cu₂P₂O₇ using XRD patterns which measured for 1 h on each sample and crystal structure of nano-C-CPO composite 54

Figure 2.5. Comparing XRD patterns of the as-prepared nano-C-CPO sample and the other nano-C-CPO sample which exposed in air for one week 55

Figure 2.6. Refined XRD pattern and crystallite size using Scherrer equation for selected h k l reflections of pristine Cu₂P₂O₇ (Rₚ＝3.11%, RI＝3.84%, RF＝4.03%, and χ²＝7.95%) XRD pattern[이미지참조] 56

Figure 2.7. Refined XRD pattern and crystallite size using Scherrer equation for selected h k l reflections of nano-C-CPO composite (Rₚ＝2.51%, RI＝4.45%, RF＝3.49%, and χ²＝2.80%) XRD pattern[이미지참조] 57

Figure 2.8. SEM image of (a) nano-C-CPO (b) pristine Cu₂P₂O₇ 60

Figure 2.9. Bright-field TEM image of nano-C-CPO composite 61

Figure 2.10. EDS elemental mapping (Cu: blue, P: purple, O: yellow, C: green) of fresh nano-C-CPO composite 62

Figure 2.11. Thermogravimetric (TGA) spectra profiles of pristine Cu₂P₂O₇ and nano-C-CPO composite 63

Figure 2.12. Electrochemical impedance spectra profiles of pristine Cu₂P₂O₇ and nano-C-CPO composite 64

Figure 2.13. (a) Power-capability of nano-C-CPO at various current rates. (b) Rate performance of nano-C-CPO 66

Figure 2.14. Power capability of pristine Cu₂P₂O₇ at various current density 67

Figure 2.15. CV curve for (a) nano-C-CPO, (b) pristine Cu₂P₂O₇ electrode measured at 5 μVs⁻¹ in the voltage range of 1.0-4.0 V 68

Figure 2.16. Cyclic performance and coulombic efficiency of nano-C-CPO over 400 cycles at 360 mA g⁻¹ after 1 cycle at 72 mA g⁻¹ 70

Figure 2.17. (a) Charge/discharge curves of nano-C-CPO at 1, 10, 50, 100, 200, 300 and 400th over 400 cycles at 360 mA g⁻¹ after 1 cycle at 120 mA g⁻¹. (b) Cyclic performance and coulombic efficiency of...[이미지참조] 71

Figure 2.18. Comparing (a) XRD patterns, (b) SEM images, (c) SAED patterns of nano-C-CPO before cycle and after 400 cycles 72

Figure 2.19. Cyclic performances of nano-C-CPO and pristine Cu₂P₂O₇ over 400 cycles at 360 mA g⁻¹ after 1cycle at 120 mA g⁻¹ 73

Figure 2.20. Operando XRD patterns of nano-C-CPO electrode during the initial cycle 76

Figure 2.21. Ex-situ XRD patterns of nano-C-CPO electrode during the initial cycle 77

Figure 2.22. Cu K-edge (a) XANES and (b) EXAFS spectra of nano-C-CPO 79

Figure 2.23. HRTEM image and SAED pattern of (a) fresh, (b) discharged, and (c) charged nano-C-CPO composite 80

Figure 2.24. HRTEM image and SAED pattern of (a) fresh, (b) discharged, and (c) charged nano-C-CPO composite 81

Chapter 3. High-energy Conversion-based Cathode Activated by Amorpholization for Li-ion Batteries 11

Figure 3.1. Scheme of fabrication process from bare Cu(PO₃)₂ to LC-CPO/C and A-CPO/C with approximate material structure images 90

Figure 3.2. Comparing XRD patterns and maximum intensities of bare Cu(PO₃)₂, LC-CPO/C and A-CPO/C 92

Figure 3.3. TEM SAED patterns of (a) A-CPO/C, (b) LC-CPO/C 93

Figure 3.4. EDS elemental mapping (Cu: yellow, P: green, O: blue) of A-CPO/C 94

Figure 3.5. Thermogravimetric (TGA) spectra profiles of bare Cu(PO₃)₂ and A-CPO/C 95

Figure 3.6. Comparing SEM images and average particle sizes of (a) A-CPO/C, (b) LC-CPO/C, (c) bare Cu(PO₃)₂. 98

Figure 3.7. XPS spectra of A-CPO/C: (a) XPS full spectrum survey, (b) Cu 2p, (c) O 1s, (d) P 2p 99

Figure 3.8. Power capability of (a) A-CPO/C and (c) LC-CPO/C at various current densities in the voltage range of 2.0-4.3 V. Rate capability of (b) A-CPO/C and (d) LC-CPO/C. 104

Figure 3.9. Comparing charge/discharge curves for pre-cycle at 12 mA g⁻¹ of A-CPO/C and LC-CPO/C. 105

Figure 3.10. Comparison charge/discharge hysteresis of A-CPO/C and LC-CPO/C electrodes measured at 12 mA g⁻¹. 106

Figure 3.11. (a) XRD pattern, (b) SEM image and average particle size of A-CPO/C_1. (c) Comparing power capability performances of samples for (c) A-CPO/C, (d) A-CPO/C_1.... 107

Figure 3.12. Comparing CV curves of (a) A-CPO/C, (b) LC-CPO/C electrode measured at 5 mV s⁻¹ in the voltage range of 2.0-4.3 V (vs. Li⁺/Li) 108

Figure 3.13. EIS measurements and values of charge transfer resistance of bare Cu(PO₃)₂, LC-CPO/C and A-CPO/C 109

Figure 3.14. (a) Power capability at various current density, (b) cycle performance for 100 cycles at 480 mA g⁻¹ of bare Cu(PO₃)₂. 110

Figure 3.15. Cycle performances of A-CPO/C and LC-CPO/C for 300 cycles at current density of 480 mA g⁻¹ after initial cycle at 30 mA g⁻¹. 112

Figure 3.16. Comparing (a) XRD patterns, (b) SEM image, (c) TEM image and SAED pattern of both of as-prepared/after 300cycles for A-CPO/C electrode 113

Figure 3.17. (a) Charge/discharge curves of A-CPO/C half-cell (vs. Li metal), full-cell (vs. graphite) and graphite half-cell (vs. Li metal) at 12 mA g⁻¹, (b) Cycle performance of A-CPO/C... 114

Figure 3.18. (a) Cut-off voltage points of ex-situ samples on charge/discharge curve of A-CPO/C. (b) Ex-situ XRD patterns of A-CPO/C. 116

Figure 3.19. Ex-situ XRD patterns of discharged A-CPO/C electrodes at 2.4, 2.6 and 2.8 V 117

Figure 3.20. HRTEM images with SAED patterns at (a) as-prepared, (b) discharged, (c) charged A-CPO/C 118

Figure 3.21. Ex-situ measurements of A-CPO/C electrodes for XANES spectra 120

Figure 3.22. Ex-situ measurements of A-CPO/C electrodes for EXAFS spectra 121

Figure 3.23. Ex-situ measurements of A-CPO/C electrodes for (a) XPS Cu 2p spectra, (b) XPS O 1s spectra 122

Figure 3.24. Ex-situ measurements of as-prepared, discharged and charged A-CPO/C electrodes for XPS P 2p spectra. 123

Figure 3.25. Comparison of energy densities (based on weights of active cathode materials) A-CPO/C and the other conventional cathodes in full-cell system 125

Chapter 4. The conversion chemistry for high-energy cathodes of sodium/potassium-ion batteries 13

Figure 4.1. Scheme of overall conversion reaction mechanism of CuSO₄ under the NIB and KIB system 134

Figure 4.2. Scheme of higher redox potential of CuSO₄ than that of CuO arising from inductive effect by sulfur with high electronegativity 135

Figure 4.3. Scheme of preparation of N-CSO/C using high-energy ball milling 141

Figure 4.4. SEM image of (a) pristine CuSO₄ and (b) N-CSO/C 142

Figure 4.5. Intensities and FWHM of XRD peaks of N-CSO/C composite and pristine CuSO₄ 143

Figure 4.6. Crystallite size of (a) pristine CuSO₄ and (b) N-CSO/C composite determined using Scherrer equation for selected h k l reflections of the XRD patterns 144

Figure 4.7. (a) Rietveld refinement of XRD pattern of N-CSO/C (Rₚ＝3.64%, RI＝1.98%, and RF＝2.12%) and detailed structural information of N-CSO/C composite[이미지참조] 145

Figure 4.8. EDS elemental mapping of N-CSO/C composite (Cu: red, S: green, O: blue, and C: yellow) 146

Figure 4.9. Thermogravimetric spectra profiles of pristine CuSO₄ and N-CSO/C composite 147

Figure 4.10. Power capability of N-CSO/C at various current density in Na cell 149

Figure 4.11. (a) Power capability (b) rate performance of N-CSO/C at various current density in K cell 150

Figure 4.12. Cyclic performance and Coulombic efficiency of N-CSO/C over 300 cycles at 720 mA g⁻¹ after 1cycle at 120 mA g⁻¹ in Na cell 151

Figure 4.13. Cyclic performance and coulombic efficiency of N-CSO/C over 200 cycles at 360 mA g⁻¹ after 1 cycle at 120 mA g⁻¹. 152

Figure 4.14. The comparison of SEM images of N-CSO/C electrodes measured (a) before cycle and (b) after 300 cycles. 153

Figure 4.15. Comparing (a) SEM images, (b) SAED patterns of N-CSO/C before cycle and after 200 cycles. 154

Figure 4.16. (a) Charge/discharge profiles at 1, 5, 10, 30 and 50th, (b) cyclic performance and Coulombic efficiency over 50 cycles at 360 mA g⁻¹ of N-CSO/C full cell in Na cell[이미지참조] 155

Figure 4.17. (a) Charge/discharge profiles of N-CSO/C|Hard-carbon full-cell at 1st, 5th, 10th, 50th, 100th, 150th, 200th, 250th and 300th cycles in K cell. (b) Cyclic performance and coulombic...[이미지참조] 156

Figure 4.18. (a) Operando XRD patterns of N-CSO/C electrode during the first cycle in Na cell (b) Ex-situ XRD patterns of N-CSO/C electrode during initial and second cycles at various... 158

Figure 4.19. (a) Operando XRD patterns of N-CSO/C electrode during the first cycle in K cell. (b) Ex-situ XRD patterns of N-CSO/C electrodes at various voltages in K cell. 159

Figure 4.20. Cu K-edge of (a) XANES (b) EXAFS spectra of N-CSO/C samples in Na cell 160

Figure 4.21. Cu K-edge of (a) XANES (b) EXAFS spectra of N-CSO/C samples in K cell 161

Figure 4.22. ToF-SIMS graphs of nano-CuSO₄/C samples during charge and discharge in Na cell 163

Figure 4.23. ToF-SIMS graphs of (a) CuSO₃⁺ (b) KSO₃⁻ (c) Cu⁺ during charge and discharge in K cell 164