Designing cost-effective and high stability cathode material : a case study on sodium iron silicate and potassium iron silicate

다국어 초록 (Multilingual Abstract)

The escalating climate crisis fueled by excessive CO₂ emissions from fossil fuel-based power and transportation systems underscores the critical need for the development of clean and sustainable energy technologies. Rechargeable batteries, particularly those used in electric vehicles (EVs) and energy storage systems (ESS), offer a promising solution. Lithium-ion batteries (LiBs) are currently being developed owing to their high energy density and stability. Concerns over the limited availability, cost, and geographic concentration of lithium have spurred the exploration of alternative chemistries based on earth-abundant elements, such as sodium and potassium. Among these, polyanionic compounds with iron-silicate frameworks have emerged as potential solutions owing to their thermal stability, low cost, and multi-electron redox activity. However, these materials face challenges, such as low electronic conductivity, sluggish ion diffusion, and polymorphic variability. This thesis addresses these challenges using targeted synthesis strategies. Chapter 2 presents an aliphatic diol-assisted hydrothermal approach for tuning the phases and morphologies of the orthosilicate-based cathodes. Chapter 3 builds on this by adjusting the diol-to-water ratio and polyol content to influence the crystallization behavior and enable in-situ carbon coating. Chapter 4 extends these methodologies to potassium analogs, allowing for structural and electrochemical comparisons. Together, these investigations aimed to develop cost-effective, high-performance cathodes for sodium- and potassium-ion batteries.
These findings not only provide valuable insights but also offer preliminary guidance for the significant advancement of orthosilicate-based cathode materials beyond lithium-ion batteries.

다국어 초록 (Multilingual Abstract)

The escalating climate crisis fueled by excessive CO₂ emissions from fossil fuel-based power and transportation systems underscores the critical need for the development of clean and sustainable energy technologies. Rechargeable batteries, particularly those used in electric vehicles (EVs) and energy storage systems (ESS), offer a promising solution. Lithium-ion batteries (LiBs) are currently being developed owing to their high energy density and stability. Concerns over the limited availability, cost, and geographic concentration of lithium have spurred the exploration of alternative chemistries based on earth-abundant elements, such as sodium and potassium. Among these, polyanionic compounds with iron-silicate frameworks have emerged as potential solutions owing to their thermal stability, low cost, and multi-electron redox activity. However, these materials face challenges, such as low electronic conductivity, sluggish ion diffusion, and polymorphic variability. This thesis addresses these challenges using targeted synthesis strategies. Chapter 2 presents an aliphatic diol-assisted hydrothermal approach for tuning the phases and morphologies of the orthosilicate-based cathodes. Chapter 3 builds on this by adjusting the diol-to-water ratio and polyol content to influence the crystallization behavior and enable in-situ carbon coating. Chapter 4 extends these methodologies to potassium analogs, allowing for structural and electrochemical comparisons. Together, these investigations aimed to develop cost-effective, high-performance cathodes for sodium- and potassium-ion batteries.
These findings not only provide valuable insights but also offer preliminary guidance for the significant advancement of orthosilicate-based cathode materials beyond lithium-ion batteries.

목차 (Table of Contents)

• Chapter 1. Introduction 1
• 1.1. Research motivation 1
• 1.2. Background on Alkali-Ion Batteries 6
• 1.3. Working Principle of Sodium Ion and Potassium Ion Batteries 9
• 1.4. Types of Cathode Materials 11
• 1.4.1. Iron Silicate Cathodes: Structure, Chemistry, and Advantages 16
• 1.4.2. Limitations and Challenges of Orthosilicate Cathodes 22
• 1.5. Scope and Objective of the Thesis 25
• Chapter 2. Unlocking the Potential of Sodium-Ion Batteries: Synthesizing Sodium Iron Silicate Cathodes Using Aliphatic Diols 28
• 2.1. Introduction 28
• 2.2. Experimental 33
• 2.2.1. Materials 33
• 2.2.2. Synthesis of NFS powders 33
• 2.2.3. Material characterization 34
• 2.2.4. Electrochemical characterization 36
• 2.3. Results and Discussion 37
• 2.4. Conclusion 64
• Chapter 3. Facet-engineered Na2FESiO4 cathodes realizing zero-strain operation and ultra-stable sodium storage 77
• 3.1. Introduction 77
• 3.2. Experimental 82
• 3.2.1. Materials 82
• 3.2.2. Synthesis of NFS powders 82
• 3.2.3. Material Characterization 83
• 3.2.4. Electrochemical characterization 85
• 3.2.5. DFT simulation 86
• 3.3. Results and Discussion 89
• 3.4. Conclusion 117
• Chapter 4. Comparative Study on A2FeSiO ₄130
• 4.1. Introduction 130
• 4.2. Experimental 133
• 4.2.1. Materials 133
• 4.2.2. Synthesis of AFS powders 133
• 4.2.3. Material Characterization 134
• 4.2.4. Electrochemical Characterization 135
• 4.3. Results and discussion 137
• 4.4. Conclusion 147
• Chapter 5. Conclusion 153
• Chapter 6. Reference 158
• Appendix A. Supplementary Data for Chapter 2 165
• Appendix B. Supplementary Data for Chapter 3 183