Title Page
Abstract
Contents
List of Abbreviations 24
List of Symbols and Units 27
1. Introduction 28
1.1. The Current Outlook of Energy Storage 28
1.2. Lithium 30
1.3. Fundamental Working Principle of Lithium-Ion Batteries 32
1.4. The Requirement for Stable Cathode Materials 36
1.5. An Introduction to Intercalation Cathodes 37
1.6. The Discovery and Development of LiCoO₂ 39
1.7. Mn Based Cathodes 44
1.8. Olivine 49
1.9. Ni-Based Layered Cathode Materials 52
1.10. The Introduction of All-Solid-State Batteries 67
1.11. Inorganic Solid Electrolytes 69
1.12. The Problems Associated with Sulfide Solid Electrolytes 70
1.13. The Cathode Composite of ASSBs 71
2. Chapter 2 74
2.1. Abstract 74
2.2. Background and Motivations 74
2.3. Experimental 79
2.3.1. Objectives 79
2.3.2. Surface Modification Method 79
2.3.3. Degradation Method 80
2.3.4. Electrochemical Characterization Method 81
2.3.5. Ball-Milling Method for Internal/External Coating Energy Dispersive Spectrometry (EDS) Analysis 81
2.3.6. Characterization Method 81
2.4. Results and Discussion 83
2.4.1. Characterization of bare and coated LiNi₀.₈Co₀.₁Mn₀.₁O₂ (NCM811) 83
2.4.2. Surface Degradation Characterization 95
2.4.3. Electrochemical Performance 107
2.4.4. Internal Degradation Evaluation and Cycle Degradation Evaluation 116
2.5. Conclusion 120
3. Chapter 3 123
3.1. Abstract 123
3.2. Background and Motivations 124
3.3. Experimental 127
3.4. Results and Discussion 130
3.5. Conclusion 138
4. Chapter 4 139
4.1. Abstract 139
4.2. Background and Motivations 139
4.3. Experimental 144
4.3.1. Materials 144
4.3.2. Composite Electrode 144
4.3.3. Surface Modification 144
4.3.4. Standard Electrochemical Measurement Cell 145
4.3.5. Carbon Material / Solid Electrolyte Side Reaction 145
4.4. Results and Discussion 146
4.4.1. Active Material and Solid Electrolyte Interface 146
4.4.2. Solid Electrolyte 150
4.4.3. Conductive Additive and Solid Electrolyte 152
4.5. Conclusion 155
5. Chapter 5 157
5.1. Abstract 157
5.2. Background and Motivations 158
5.3. Experimental 162
5.3.1. Materials 162
5.3.2. Synthesis of Functionalized CNF 163
5.3.3. Synthesis of Acid-Functionalized CNF (F-CNF) 163
5.3.4. Synthesis of Lithium Enhanced Acid-Functionalized CNF (LF-CNF) 164
5.3.5. Synthesis of Hydroxyl-Functionalized CNF (KOH-CNF) 164
5.3.6. Preparation of Cell Material Composites 165
5.3.7. Preparation of CNF/SE Composites for EIS 165
5.3.8. Preparation of CNF/SE Composites for Stripping/Plating Tests 165
5.3.9. Cells Assembly 166
5.3.10. Standard Cell for Electrochemical Measurement (2-3) 166
5.3.11. CNF/SE Cell for Electrochemical Measurement 166
5.3.12. CNF-Only Cell for Stripping/Plating Measurement 167
5.3.13. Electrochemical Measurements 167
5.3.14. CNF/SE Cell for EIS Measurement (1) 167
5.3.15. Galvanostatic Cycling of Standard Cell 167
5.3.16. Galvanostatic Cycling of Lithium Stripping/Plating 168
5.3.17. Galvanostatic Cycling of Rate Increased Cell 168
5.3.18. Characterization 168
5.4. Results and Discussion 169
5.4.1. Preparation and Characterizations of P-CNF, F-CNF, and LF-CNF 169
5.4.2. The Impact of Functionalization on the Ionic and Electrical Conductivity 179
5.4.3. Determining the Effect of LF-CNF on the Active Material via Surface Analysis 195
5.5. Conclusion 198
6. References 201
Abstract (Korean Version) 225
7. Appendix 227
7.1. Declaration of Published Work: Chapter 2 227
7.2. Declaration of Published Work: Chapter 3 227
7.3. Declaration of Published Work: Chapter 5 229
Table 1-1. Description of important Lithium properties. (V vs. SHE=Voltage vs. standard hydrogen electrode) - Adapted from [12] 31
Table 1-2. The benefits of increasing the cut-off voltage of LiCoO₂ as adapted from [39] 41
Table 1-3. The parameter trends of NCM materials based on their individual constituent elements adapted from [90]. 56
Table 1-4. Comparison of the properties for the discussed cathode materials, adapted from [123] 65
Table 3-1. Electrochemical results summary for single crystal materials 137
Table 4-1. Electrochemical data summary of the coated cathode material applied in the solid electrolyte composite. 150
Table 5-1. Literature comparison between mostly non-coated pristine NCM cathode materials in sulfide electrolyte composites. 191
Figure 1.1. Novel use cases for lithium-ion batteries in energy storage and transport. 28
Figure 1.2. The elemental Lithium and its atomic structure 30
Figure 1.3. Schematic representation of a Lithium-ion cell applying a layered intercalation cathode and a graphite intercalation anode. 32
Figure 1.4. The requirement for increasing Ni-ratio in the cathode active material to maximize the energy density of standard Li-ion batteries as adapted from [18] 36
Figure 1.5. Layered structure of LiCoO₂ highlighting the degradation mechanism associated with high levels of discharge. Adapted from [31] 40
Figure 1.6. The history of the LiCoO₂ cathode material and the move towards higher specific capacities. Adapted from [36] 41
Figure 1.7. Examples of the layered and spinel forms of LiMnO₂ with their corresponding distortion mechanism, as adapted from [58] 45
Figure 1.8. Example of Li₂MnO₄ cathode spinel structure as adapted from [71] 47
Figure 1.9. Olivine structure of LiFePO₄ during the charge / discharge process with full removal of Lithium ions as adapted from [86] 50
Figure 1.10. Comparison of the properties of the commercialized layered, spinel and olivine cathodes of LiCoO₂, Li₂MnO₄ and LiFePO₄. Adapted from [87] 51
Figure 1.11. Layered structure of LiNiO₂ and the degradation mechanism associated with its extended cycling. 52
Figure 1.12. The comparison between the ion size of Li⁺, Ni²⁺, and Ni³⁺ showing the propensity of Ni²⁺ to cation mix as adapted from [93] 53
Figure 1.13. The layered structure of Lithium Nickel Manganese Cobalt Oxide (NCM) and the corresponding propensity of the material to cation mix. 54
Figure 1.14. The redox energies of cathode materials relative to the anion: p band which must be avoided as adapted from [90]. The phase diagram of typical NCM... 56
Figure 1.15. The timeline of the development and research of Ni-rich cathode materials adapted from [105] 58
Figure 1.16. Differential capacity analysis example for an NCM cell with stable cut-off at 4.2 V as adapted from [118] 62
Figure 1.17. Potential and specific capacity comparisons for the discussed commercialized cathode materials as adapted from [123] 64
Figure 1.18. Summary of the performance of NCM materials and a short analysis of the cost of NCM materials and the relation to cobalt content as adapted from [126] 66
Figure 1.19. Comparison between liquid electrolyte lithium-ion batteries, current solid-state lithium-ion batteries and future high-capacity solid-state lithium-ion... 68
Figure 1.20. Comparison between the most discussed properties of organic liquid electrolyte systems and inorganic solid electrolyte systems. 69
Figure 1.21. Highlighting the current poorer performance of solid-state batteries in laboratory research and the predicted and required performance levels that... 72
Figure 2.1. Schematic illustration of the coating mechanisms proposed in this work showing their effectiveness of protecting ability according to the coating morphology. 78
Figure 2.2. The objectives of this research as were outlined before the start of the experiments. 79
Figure 2.3. Schematic of the coating treatment performed for the sol-gel coating using acetate precursors and ethanol solvent. 80
Figure 2.4. Characterization of bare and coated LiNi₀.₈Co₀.₁Mn₀.₁O₂ (NCM811) materials. Ion-milled Scanning Electron Microscopy (SEM) images of a) the... 83
Figure 2.5. a) Point EDS detecting the wt.% of Sn at various ball-milled primary particles of Li₂SnO₃ coated NCM811. b) Point EDS detecting the wt.% of Co at... 85
Figure 2.6. Average additional wt.% of Co or Sn detected in the respective samples after ball-milling to show internal and external primary particles surfaces. 86
Figure 2.7. The scanning electron microscopy (SEM) and Energy dispersive spectroscopy elemental mapping (EDS) of Li₂SnO₃ (Top) coated NCM811 material... 87
Figure 2.8. Average additional wt.% of Co or Sn detected in the respective samples without ball-milling to show only external secondary particles surfaces. 88
Figure 2.9. Bare sample EDS Point analysis displaying the exact location and detailed composition of the transition metals at these points. 89
Figure 2.10. LiCoO₂ coated sample EDS Point analysis displaying the exact location and detailed composition of the transition metals at these points. 90
Figure 2.11. Li₂SnO₃ coated sample EDS Point analysis displaying the exact location and detailed composition of the transition metals at these points. 91
Figure 2.12. EDS Point analysis of Bare, Li₂SnO₃ and LiCoO₂ 5 wt.% coated samples showing the increase in Co detected at the outer surface of the internal... 92
Figure 2.13. Powder X-Ray Diffraction (XRD) analysis of Bare NCM811, LiCoO₂ coated NCM811 and Li₂SnO₃ coated NCM811 material in the electrode. 93
Figure 2.14. 35⁰ peak of Li₂SnO₃ and~42⁰ peak of Li₂SnO₃ 94
Figure 2.15. Coating of NCM811 material pre-annealing with a) Co and Li precursors, b) Sn and Li precursors. 95
Figure 2.16. The scanning electron microscopy (SEM) imaging of NCM811 Bare Sample degraded in a) Air b) Moisture (100%) and c) Heated Air (80℃). 97
Figure 2.17. The scanning electron microscopy (SEM) imaging of NCM811 Bare Sample degraded in a) Air b) Moisture (100%) and c) Heated Air (80℃) and then... 99
Figure 2.18. The scanning electron microscopy (SEM) imaging of Li₂SnO₃ coated NCM811 Sample degraded in a) Air b) Moisture (100%) and c) Heated Air (80℃) 101
Figure 2.19. The scanning electron microscopy (SEM) imaging of LiCoO₂ coated NCM811 Sample degraded in a) Air b) Moisture (100%) and c) Heated Air (80℃) 102
Figure 2.20. The Scanning Electron Microscopy (SEM) imaging of a) Bare NCM811 in the pristine state, b) Bare NCM811 in the air degraded state, c) Bare... 104
Figure 2.21. Lithium titration composition results for pristine and moisture degraded samples showing presence of LiOH and Li₂CO₃ residuals throughout the particles. 106
Figure 2.22. Electrochemical data showing the voltage profile for the pristine samples. 108
Figure 2.23. Electrochemical performance of bare and coated NCM811s that were exposed to various atmospheric conditions. The electrochemical cycle data over 50 cycles... 109
Figure 2.24. The scanning electron microscopy (SEM) images and image processed pore analysis of a) Bare NCM811 sample before degradation, b) LiCoO₂... 110
Figure 2.25. Electrochemical Impedance spectroscopy (EIS) data of the pristine samples cycled for 50 cycles. 111
Figure 2.26. Electrochemical performance of bare and coated NCM811s that were exposed to various atmospheric conditions. The electrochemical cycle data... 115
Figure 2.27. Powder X-ray diffraction (XRD) patterns of the degraded NCM811s (Bare, LiCoO₂ coated and Li₂SnO₃ coated NCM811s). 116
Figure 2.28. (003) characteristic peaks for the degraded NCM811s. 117
Figure 2.29. The scanning electron microscopy (SEM) Imaging of heat degraded ion-milled a-b) Bare NCM811 after 50 cycles, c-d) Li₂SnO₃ coated after 50 cycles,... 118
Figure 2.30. Schematic illustration for surface degradation mechanism. 120
Figure 3.1. Schematic describing the process going from untreated polycrystalline LiNi₀.₈Co₀.₁Mn₀.₁O₂ (NCM811) material to single crystal NCM... 129
Figure 3.2. Scanning electron microscopy (SEM) images of a) bare NCM811 b) Li₂SnO₃ coated NCM811 and c) LiCoO₂ coated NCM811 polycrystals after the sol-... 131
Figure 3.3. Electrochemical data for coated and untreated polycrystalline samples showing a) formation cycle voltage profile at 0.1 C, b) Discharge capacity... 133
Figure 3.4. (SEM) images of a) bare NCM811 b) Li₂SnO₃ coated NCM811 and c) LiCoO₂ coated NCM811 single crystals after the 2-step sintering/annealing process. 135
Figure 3.5. Electrochemical data for coated and untreated single crystal samples showing d) formation cycle voltage profile at 0.1 C, e) Discharge capacity over 50... 136
Figure 4.1. Comparison between safer alternatives to layered cathode based traditional Lithium-ion batteries. 143
Figure 4.2. Scanning electron microscopy images of pre-annealed a) Li₂SnO₃ coated NCM811 and c) LiCoO₂ coated NCM811 and post-annealed b) Li₂SnO₃... 147
Figure 4.3. Voltage profile for pristine, Li₂SnO₃ coated and LiCoO₂ coated NCM811 with inset highlighting the slight overpotential reduction associated with... 148
Figure 4.4. Cycle data over 5 cycles for pristine, Li₂SnO₃ coated and LiCoO₂ coated NCM811. 149
Figure 4.5. Comparison of a) ratio and b) morphology change of solid electrolyte in the cathode composite. 151
Figure 4.6. Comparison of the carbon additive materials in the cathode composite with inset highlighting the side reactions. 152
Figure 4.7. Direct analysis of side reactions between the carbon conductive additive and the solid electrolyte at cathode half-cell bias. 153
Figure 4.8. The cycle data showing a) coulombic efficiency and b) discharge capacity for an NCM811-based cathode composite with differing carbon additive material. 154
Figure 5.1. The cathode composite of solid-state batteries and the associated side reaction interfaces shown in red. 159
Figure 5.2. Schematic outlining the mechanisms of functionalized carbon nanofiber in the cathode composite. The cathode composite with a) Super-C, b)... 160
Figure 5.3. Methods for producing the various functionalized CNF materials including F-CNF, LF-CNF. 163
Figure 5.4. The ion swapping process for exchanging H⁺ with Li⁺ on the carboxylic group. 164
Figure 5.5. Schematic showing the various cell set-ups with the numbers shown in the methods section. 166
Figure 5.6. Characterizing the functionalization of CNF material. Scanning electron microscopy (SEM) imaging of the surface of P-CNF, F-CNF and LF-CNF. 169
Figure 5.7. EDS element analysis of a) P-CNF and b) F-CNF with the elemental table at c). 171
Figure 5.8. Raman spectra showing Defect (D) and Graphite (G) peak ratio for P-CNF, F-CNF and LF-CNF. 171
Figure 5.9. Fourier-transform infrared spectroscopy (FT-IR) spectra for P-CNF, F-CNF, and LF-CNF. 173
Figure 5.10. F-CNF FTIR data with galvanically cycled F-CNF between two lithium plates showing left shift with b) peak analysis of the cycled P-CNF showing... 174
Figure 5.11. X-ray photoelectron spectroscopy (XPS) spectra of the O1s region for a) P-CNF b) F-CNF and c) LF-CNF. 175
Figure 5.12. XPS data for C1s peaks for a) P-CNF, b) F-CNF and c) LF-CNF. 175
Figure 5.13. XPS data for O1s, C1s, and Na1s peaks for Na-ion swapped F-CNF. a) O1s peak, b) C1s, and c) Na1s peak deconvolution for Na ion swapped F-CNF. 176
Figure 5.14. XPS O1s spectrum for KOH-CNF and XPS C1s spectrum for KOH-CNF 177
Figure 5.15. Formation voltage profile for all-solid-state cells utilizing Na-CNF, KOH-CNF and Li-KOH-CNF 178
Figure 5.16. The functionalization effect on ionic and electrical conductivity. a) Electrochemical impedance spectroscopy (EIS) measurements for P-CNF, F-CNF... 179
Figure 5.17. Pellet measurements required for calculation of ionic conductivity. 181
Figure 5.18. Side reactions of the carbon interaction with the solid electrolyte. 182
Figure 5.19. EIS data for a) Active Material (AM): Solid Electrolyte (SE): Carbon Additive (CA) ratio 70:30:5 cell and b) AM:SE:CA ratio 80:20:5. c) Data showing... 184
Figure 5.20. a) Image of 10 wt.% P-CNF, F-CNF and LF-CNF in binder cast onto glass. b) Resistance of P-CNF, F-CNF and LF-CNF 10 wt.% in binder calculated... 186
Figure 5.21. Electrochemical performance of half-cell with varying conductive materials. Cycle data for a) Super-C, b) P-CNF and c) LF-CNF cells at 0.1 C over... 187
Figure 5.22. Voltage profile of formation for a) P-CNF, F-CNF and LF-CNF at AM:SE:CA ratio of 70:30:5, b) P-CNF and LF-CNF at AM:SE:CA ratios of... 190
Figure 5.23. Cycled data comparing the different functionalization times for F-CNF material. a) Discharge capacities and Coulombic efficiencies of F-CNF 12 Hr (blue),... 192
Figure 5.24. a) dQ/dV analysis for the formation charge/discharge of P-CNF and LF-CNF at 0.05C. b) Charge/discharge C-rate increase for LF-CNF and P-CNF at 0.5C... 193
Figure 5.25. Stability effects at the cathode surface during storage and cycling. a) Powder X-ray diffraction (XRD) analysis of composite (AM:SE:CA 70:30:5) after 1... 195
Figure 5.26. X-ray photoelectron spectroscopy (XPS) analysis of Ni content at the surface of a) LF-CNF Composite after cycling at 4.5 V and b) P-CNF Composite after... 197
Figure 5.27. dQ/dV analysis of the P-CNF and LF-CNF cells before and after cycling showing irreversible peak shift. 198
Figure 5.28. The relationship between the solid electrolyte (SE) and the LF-CNF. The relationship between active material (AM) and LF-CNF. The relationship between the... 200