Interfacial Structure Design and Lithium- Ion Transport Mechanisms of Rare-Earth- Regulated Polymer Composite Electrolytes = 희토류조절폴리머복합전해질의계면구조설계및리튬 이온전달메커니즘

다국어 초록 (Multilingual Abstract)

Polymer electrolytes have been widely studied for high-safety lithium metal batteries （LMBs）, mainly because they have good flexibility, processability, and can form relatively close contact with electrodes. Even so, several problems have not been fully solved, including slow Li+ transport, strong Li+–anion interaction, serious interfacial polarization, unstable lithium deposition, and poor long-term cycling stability. Around these issues, this dissertation introduces rare-earth regulation into polymer composite electrolytes, and discusses how this strategy affects interfacial structure design and lithium-ion transport behavior. Two electrolyte systems were selected for this study: one is a quasi-solid-state system, and the other is an all-solid-state system. Through these two systems, the role of lanthanum in regulating anion behavior, Li+ transport, and interfacial stability at different structural levels can be more clearly understood. One part of this work is based on a La@ZIF-8/SiO2/PAN composite quasi-solid electrolyte （CQSE）, which was designed as a structure- regulated electrolyte system. This part synthesizes La@Zeolitic imidazolate frameworks-8 （La@ZIF-8） metal-organic framework （MOF） xviii nanoparticles as a coating material for CQSE. Theoretical calculations and experimental results revealed that incorporating the high-valent rare earth experimental results showed that incorporating the high-valent rare earth element La（Ⅲ） effectively improves the anion-anchoring effect, makes weaker its binding with Li+ ions, and helps with the dissociation of lithium salts. Simultaneously, the polarization phenomenon is reduced, promoting stable lithium detachment and embedding in the electrodes. The CQSE made of La@ZIF-8/SiO2/PAN is produced by embedding SiO2 nanoparticles into robust polyacrylonitrile （PAN） fiber membranes, followed by surface coating with La@ZIF-8 MOF. As a result, the La@ZIF-8/SiO2/PAN CQSE shows an ionic conductivity of 6.76 × 10-4 S/cm and a Li+ transfer number of 0.67 at room temperature （25 °C）, with an initial discharge capacity of the La@ZIF-8/SiO2/PAN battery at 138.61 mAh g-1. The capacity retention rate was 94.43% after 200 cycles, with a capacity decay rate of only 0.02785% per cycle. In this way, La@ZIF- 8/SiO2/PAN CQSE exhibits excellent electrochemical performance and cycling stability, ensuring the efficient and safe utilization of quasi-solid- state lithium-metal batteries. Second, a lanthanum-enriched PEO （LP） composite electrolyte was constructed by introducing lanthanum formate molecular （LaMe） clusters into the PEO matrix. This system represents a molecular level regulation route. The Lewis-acidic La–O sites immobilized TFSI- anions, weakened Li+–TFSI- association, and increased the amount of free Li+ carriers. At the same time, the interaction between LaMe and PEO reduced local crystallinity and promoted polymer-chain motion, forming continuous Li+ transport pathways. Electrochemical and theoretical analyses further showed that LaMe lowered the HOMO level, widened the electrochemical window, and supported low energy barrier Li+ migration. As a result, the LP electrolyte showed high ionic conductivity, high Li+ transfer number, and strong interfacial compatibility. Li||Li symmetric batteries cycled steadily for over 2000 h at 1.0 mA cm-2. Li||LFP batteries retained 94.61% of their capacity after 300 cycles at 0.5 C, and also sustained 1000 cycles at 4.2 V with nearly 100% Coulombic efficiency. By comparing these two electrolyte systems, this dissertation summarizes two rare-earth regulation routes that can be used for polymer electrolytes. One route works mainly through structural regulation in the quasi-solid-state system, while the other works through molecular-level regulation in the all-solid-state system. The two systems are not the same in structure or transport environment, but they point to a similar mechanism: rare-earth functional sites can regulate anion behavior, make Li+ transport more selective, and help build a more stable electrode/electrolyte interface. In this sense, the comparison does not only show the performance difference between the two systems, but also helps explain how rare-earth regulation can be used to design safer, high-voltage, and long-life polymer electrolytes for LMBs. KEYWORDS: Rare-earth-regulated polymer electrolytes; Lithium-ion transport; Anion anchoring; Interfacial stabilization; Lithium metal batteries

목차 (Table of Contents)

• Chapter 1 Introduction 1
• 1.1 Background 1
• 1.2 Current Research Status of Polymer Electrolytes 3
• 1.2.1 Current Research Status of Composite Quasi-Solid Electrolytes 3
• 1.2.2 Current Research Status of PEO-Based Solid Electrolytes 6
• 1.3 Research Status of Ion Transport and Interface regulation and Rare Earth Regulation Strategies 8
• 1.4 Research Content 12
• Chapter 2 Experimental Materials and Characterization 15
• 2.1 Experimental Materials and Instrument Equipment 15
• 2.1.1 Materials 15
• 2.1.2 Instruments and Equipment 16
• 2.2 Preparation of Electrolytes 16
• 2.2.1 Preparation of La@ZIF-8/SiO2/PAN CQSE 16
• 2.2.2 Preparation of LaMe/PEO Solid Electrolyte 19
• 2.2.3 Battery Assembly Method 21
• 2.3 Material Characterization 22
• 2.4 Electrochemical and Theoretical Calculation Methods 24
• 2.4.1 Ion Transport Performance 24
• 2.4.2 Electrochemical Window and Battery Cycle Test 25
• 2.4.3 Theoretical Calculation 26
• Chapter 3 Design Strategy for Rare-Earth-Regulated Polymer Electrolytes 28
• 3.1 Main Limiting Factors of Ion Transport in Polymer Electrolytes 28
• 3.2 Fundamental Principle of Rare-Earth Regulation of Anions 30
• 3.3 Fundamental Principles of Rare-Earth Regulation of Interfaces 32
• 3.4 Overall Design Strategy of the Present Study 35
• Chapter 4 Research on La@ZIF-8-Enhanced CQSE for High-Performance Li-Metal Batteries 37
• 4.1 Material Design and Structural Construction of CQSE. 37
• 4.1.1 The Design and Preparation of La@ZIF-8 MOF 37
• 4.1.2 The Function and Structure of La@ZIF-8/SiO2/PAN CQSE. 39
• 4.2 Structural and Physicochemical Characterization 44
• 4.2.1 Morphological and Compositional Analysis 44
• 4.2.2 Electrolyte Uptake and Electrolyte Retention 53
• 4.2.3 Mechanical Property and Thermal Stability Analysis 56
• 4.3 Electrochemical Characterization and MechanismAnalysis 62
• 4.3.1 Electrochemical Characterization 62
• 4.3.2 Anion Anchoring and Li+ Migration 67
• 4.4 Battery Performance and Interface Stability 70
• 4.4.1 Performance Analysis of Symmetrical Batteries 70
• 4.4.2 Battery Cycle Performance and Interface Stability 74
• 4.5 Summary 82
• Chapter 5 Ion Transport and Interface Stabilization Mechanisms in LaMe/PEO Solid-State Composite Electrolytes 84
• 5.1 Research Objectives and Strategy 84
• 5.2 The Structural Basis and Functional Characteristics of LaMe/PEO Electrolytes 87
• 5.2.1 Structural Characterization and Anion Adsorption of LaMe 87
• 5.2.2 Selection of LaMe Content and Representative Samples 92
• 5.3 Mechanism of Li+ Transport Regulation by LaMe 94
• 5.3.1 Synergistic Modulation of the Local Coordination Environment and Li+ Transport by LaMe 94
• 5.3.2 DFT Study on the Low-Barrier Migration of Li+ 102
• 5.4 Effect of LaMe on Interfacial Stability and Battery Performance 108
• 5.4.1 Interface Stability Behavior in Symmetrical Batteries 108
• 5.4.2 Rate Performance and Long-Term Cycling of Full Cells 112
• 5.4.3 Stable Interface Formation and Ion Sieving Behavior 118
• 5.5 Summary 123
• Chapter 6 Comparison between the Two Rare-Earth Regulation Methods 126
• 6.1 Structural Features of the Two Electrolyte Systems 126
• 6.2 Comparison of the Ion Transport Mechanisms of the Two Systems 129
• 6.2.1 Comparison of Anion Regulation Modes 129
• 6.2.2 Comparison of Li+ Transport Enhancement Mechanisms 130
• 6.2.3 Summary of Ion Transport Principles 132
• 6.3 Comparison of Interfacial Stabilization in the Two Systems 133
• 6.4 Design Principles for Rare-Earth-Regulated Polymer Electrolytes 141
• Chapter 7 Summary and Outlook 144
• 7.1 Summary 144
• 7.2 Outlook 146
• References 148
• Publications 158
• Abstracts 164