Studies on Compositions of High Performance Electrolytes and Evaluations of Characteristics for Lithium Ion Secondary Batteries

다국어 초록 (Multilingual Abstract)

In chapter 1, electrolyte industry and development for Li-ion batteries were described. The next-generation lithium salt, which is the core electrolyte material currently being developed in this project, has the advantages of realizing high output at room and low temperatures, extending charge/discharge life, and corrosion prevention efficiency compared to the existing LiPF6.
In chapter 2, Electrolyte composition and commercialization technology using new lithium salts, solvents, additives were studied. Established a high-performance electrolyte analysis platform for electric vehicles and conducted research on electrolyte deterioration mechanisms due to long lifespan/high temperature storage/high voltage operation. Gas generation mechanisms during life and development of solvents and additives to suppress gas generation were investigated. Research on gas generation mechanisms under high temperature environments and development of additives to suppress gas generation was performed.
In chapter 3, Based on the results of the study in Chapter 2, optimal electrolyte composition conditions were established, new additives were designed and synthesized, and composition combination studies were conducted. Protective film formation mechanism of ternary anode and development of new electrolyte were investigated. Investigation of protective film formation mechanism of high-density cathode and development of new electrolyte solution were performed.
In chapter 4, we aim to develop new functional materials for high rate charging without loss of energy density and verify element technologies through electrode and cell design to verify effectiveness. Existing commercialized electrolytes for lithium secondary batteries have low impregnation characteristics into high composite electrode plates due to their high viscosity, and there are questions about whether they can form an electrode interface suitable for rapid charging conditions. Therefore, this project seeks to develop high energy density (≥260 Wh/kg) lithium-ion secondary battery technology capable of high-rate charging (10 min/SOC 10 ~ 80%).
In chapter 5, quasi-solid electrolytes with enhanced ignition/explosion safety applicable to Li-ion batteries for energy storage systems were studied. There were studied flame retardant additives to control reactivity with electrodes, and development of space-intensive flame retardant/non-flammable additive structure and separator technology by coating ceramic flame retardants on the separator. Applicability of quasi-solid electrolyte to electrode plates and unit cells was verified.

목차 (Table of Contents)

• List of Tables ⅴ
• List of Figures and Schemes ⅵ
• Abstract ⅹ
• Chapter 1. General Introduction of Electrolytes of Lithium Battery 1
• 1.1. Li-ion batteries · 1
• 1.2. Electrolytes for Li-ion batteries 3
• 1.3. Electrolyte Strategy and object · 8
• Chapter 2. Research on optimal electrolyte composition using new additives 10
• 2.1. Introduction · 10
• 2.2. Materials and Methods 11
• 2.1.1. Types of electrolytes · 11
• 2.2.2. Solvent selection 12
• 2.2.3. Salt selection 12
• 2.2.4. Selection of additives 12
• 2.2.5. Electrolyte manufacturing and analysis 13
• 2.3. Results and Discussion 14
• 2.3.1. Analysis of anode reactivity through linear sweep voltammetry (LSV) ··
• 14
• 2.3.2. Analysis of reactivity with anode and cathode through cyclic voltammetry
• (CV) 14
• 2.3.3. Lifespan characteristics evaluation results 15
• 2.3.4. EIS analysis results before and after life characteristics evaluation · 15
• 2.3.5. Full-cell lifespan characteristics evaluation results 16
• 2.3.6. SEM analysis after life evaluation 17
• 2.3.7. SEI layer analysis through SEM and XPS after life evaluation 18
• 2.3.8. XPS analysis results · 18
• 2.3.9. Lifespan characteristics evaluation results 19
• 2.3.10. EIS analysis results before and after life characteristics evaluation at
• high temperature 19
• 2.3.11. Selection of developed electrolyte · 20
• 2.3.12. Evaluation of electrochemical properties of developed electrolyte 21
• 2.3.13. Selection and evaluation of gas generation suppression additive
• candidates 22
• 2.3.14. Evaluation of physical properties according to solvent ratio and
• evaluation of reactivity with electrodes · 24
• 2.3.15. Evaluation of electrochemical properties according to solvent ratio ·· 25
• 2.4. Conclusions · 27
• 2.4.1. Development and selection of new additives 27
• 2.4.2. Pouch cell evaluation of selected additives and new additives · 28
• 2.4.3. Fluorine/non-fluorine selection additive pouch cell evaluation 31
• Chapter 3. Research on electrolyte composition and physical properties for high
• energy density lithium secondary batteries 33
• 3.1. Introduction · 33
• 3.2. Materials and Methods 34
• 3.2.1. Evaluation environment for target items 35
• 3.3 Results and discussion · 37
• 3.3.1. Derivation of optical candidates and contents of electrolyte additive ·· 37
• 3.3.2. Search for fluorin-based additive materials 41
• 3.3.3. Research on the synthesis of fluorine-based additives · 41
• 3.3.4. Evaluation of fluorine-based additives · 43
• 3.3.5. Linear Sweep Voltammetry (LSV) 43
• 3.3.6. Cyclic Voltammetry (CV) · 44
• 3.3.7. Charge/discharge test 45
• 3.3.8. Secondary search for fluorine-based additive materials 46
• 3.3.9. Evaluation of 5 types of fluoro synthetic structures · 46
• 3.3.9.1. Precycling data 47
• 3.3.9.2. Cycle data · 48
• 3.3.10. Additive effect of reference electrolyte GEN0 48
• 3.3.10.1. LiBOB/LiDFOB additives and use background 48
• 3.3.10.2. Physical properties of electrolyte added with LiBOB/LiDFOB ·· 49
• 3.3.10.3. Fabrication and charge/discharge test of NCM811/Li half cell 50
• 3.3.10.4. Charging and discharging conditions 51
• 3.3.10.5. Additive characteristics of NCM811/Li half cell (when adding
• LiBOB/LiDFOB) 52
• 3.3.10.6. Cycle characteristics 53
• 3.3.10.7. Impedance (bulk and interfacial resistance) 54
• 3.3.10.8. Resistance increase rate for GEN-series electrolyte 55
• 3.3.10.9. High-temperature storage characteristic of GEN-series electrolyte
• (capacity recovery rate) · 57
• 3.5. Conclusion 60
• Chapter 4. Development of electrolyte composition for rapid charging and
• evaluation of battery characteristics 66
• 4.1. Introduction · 66
• 4.2. Experimental, Result and discussion 69
• 4.2.1. Promotion contents 69
• 4.2.2. Development electrolyte composition design and physical property
• evaluation 69
• 4.2.2.1. 1st developed electrolyte for improving high rate charging 69
• 4.2.2.2. Evaluation of properties of 1st developed electrolyte 69
• 4.2.2.3. Electrochemical evaluation of 1st developed electrolyte for improving
• high rate charging 71
• 4.2.2.4. Evaluation of 1st developed electrolyte pouch cell 72
• 4.2.3. Secondary development electrolyte composition for improving high-rate
• charging · 74
• 4.2.3.1. Evaluation of properties of 2nd developed electrolyte 74
• 4.2.3.2. Electrochemical evaluation of developed electrolyte for improving high-
• rate charging 75
• 4.2.3.3. Coin-cell evaluation 76
• 4.2.4. 3rd development electrolyte composition design and physical property
• evaluation 79
• 4.2.4.1. Electrolyte composition for improving high-rate charging 79
• 4.2.4.2. Evaluation of properties of 3rd developed electrolyte 79
• 4.2.4.3. Viscosity evaluation of developed electrolyte 80
• 4.2.4.4. Electrochemical evaluation of developed electrolyte for improving high-
• rate charging 81
• 4.2.4.5. Development electrolyte coin-cell evaluation 82
• 4.3. Conclusion 85
• Chapter 5. Optimization and characterization of solid electrolyte composition based
• on flame retardant polymer 86
• 5.1. Introduction · 86
• 5.2. Goal and purpose 89
• 5.3. Results and discussion· 91
• 5.3.1. Ion conductivity: Evaluation of ionic conductivity according to additives
• 91
• 5.3.2. Electrochemical stability (Li/Li+): Linear Sweep Voltammetry (LSV) · 91
• 5.3.3. Pouch cell evaluation 92
• 5.3.4. Electrolyte composition 92
• 5.3.5. Evaluation conditions 93
• 5.3.6. Formation · 93
• 5.3.7. Evaluation of lifespan characteristics 94
• 5.3.8. Evaluation of storage characteristics 95
• 5.4. Conclusion 97
• References · 99
• Abstract (in Korean) 112