Synthesis and application of polyimide precursor binder for high-capacity silicon anodes

국문 초록 (Abstract)

본 연구는 리튬이온배터리 전극에서 폴리이미드(PI) 바인더를 적용하여, 고로딩 및 대변형 조건 하에서 접착력과 계면 안정성을 향상시키는 동시에 전극 저항과 수명 성능 간의 균형을 유지하기 위한 실질적인 설계 지침을 확립하는 것을 목표로 합니다. 이를 위해 비수계 NMP 기반 PAmA-to-PI 경로와 TEA 및 DMIZ 이온화를 기반으로 한 수계 전구체 경로를 동일한 전극 설계 프레임워크 하에서 체계적으로 비교하였습니다. 수계 전구체 경로에서는 PEGDE를 이용한 in-situ 가교를 도입하여 바인더 네트워크의 기계적 강도와 계면 안정성을 강화하였습니다.

공정 관점에서는 집전체 및 활물질의 열적 허용 한계를 고려하여, 150 °C의 저온 이미드화 프로파일을 적용함으로써 현실적인 공정 윈도우를 정의하였습니다. 또한 **Taguchi L27 실험 설계(바인더 함량–도전재 함량–면적 로딩, 3 × 3 × 3)**를 활용하여 각 인자의 영향도와 지배성을 정량적으로 평가하였습니다. 평가 지표로는 180° 박리 접착 강도, 전극 및 입자 저항, 전기화학 임피던스 분광법(EIS, Rs 및 Rct), 초기 쿨롬 효율, 속도 특성, 그리고 장기 사이클 성능을 포함하였습니다.

그 결과, 접착력, 초기 효율, 사이클 유지율을 지배하는 주요 인자는 일관되게 바인더 > Super-P > 로딩의 순서를 따르는 것으로 나타났으며, 조사된 범위 내에서는 인자 간 상호작용 효과는 제한적인 것으로 확인되었습니다. 가교가 없는 PI를 기준으로 수계 및 비수계 경로를 비교한 결과, 수계 경로는 안전성, 환경 친화성, 공정성 측면에서 뚜렷한 장점을 보였습니다. 더 나아가, DMIZ/TEA 기반 시스템에 in-situ 가교를 적용한 경우, 캘린더링 이후에도 전극 구조의 건전성을 유지하고 Rct의 장기적 증가를 억제하는 경향을 나타냈습니다. 또한 저온 이미드화 조건에서도 충분한 이미드화 진행과 전해액 안정성이 확인되었습니다.

본 연구는 고로딩 전극에서 성능, 공정성, 신뢰성 요구사항을 동시에 충족하는 최적의 조성 및 공정 윈도우를 제안합니다. 수계 공정, in-situ 가교, 저온 이미드화 전략을 통합함으로써, 본 연구는 차세대 고에너지 리튬이온배터리 전극을 위한 PI 바인더의 산업적 적용 가능성을 명확히 입증합니다.

다국어 초록 (Multilingual Abstract)

This study aims to establish practical design guidelines for improving adhesion and interfacial stability under high-loading and large-deformation conditions while maintaining a balance between electrode resistance and lifetime performance through the application of polyimide (PI) binders in lithium-ion battery electrodes. A non-aqueous NMP-based PAmA-to-PI route is systematically compared with an aqueous precursor route based on TEA and DMIZ ionization under an identical electrode design framework. The aqueous precursor route incorporates in situ crosslinking using PEGDE to enhance the mechanical robustness and interfacial stability of the binder network. From a processing perspective, a low-temperature imidization profile at 150 °C is established to define a feasible process window considering the thermal budget limitations of the current collector and active material. A Taguchi L27 experimental design (binder content–conductive agent content–areal loading, 3 × 3 × 3) is employed to quantitatively evaluate the influence and dominance of each factor. The evaluation metrics include 180° peel adhesion strength, electrode and particle resistance, electrochemical impedance spectroscopy (Rs and Rct), initial coulombic efficiency, rate capability, and long-term cycling performance. The results demonstrate that the primary factors governing adhesion, initial efficiency, and cycle retention consistently follow the order of binder > Super-P > areal loading, with limited interaction effects within the investigated ranges. In comparisons of non-crosslinked PI prepared via aqueous and non-aqueous routes, the aqueous route exhibits clear advantages in safety, environmental compatibility, and processability. Moreover, the DMIZ/TEA-based system with in situ crosslinking shows a favorable tendency to maintain electrode integrity and suppress the long-term increase in Rct after calendaring. Sufficient imidization progress and electrolyte stability are also confirmed even under the low-temperature imidization condition. This study proposes an optimized composition and process window that simultaneously satisfy the performance, processability, and reliability requirements of high-loading electrodes. By integrating aqueous processing, in situ crosslinking, and low-temperature imidization strategies, this work demonstrates the industrial applicability of PI binders for next-generation high-energy lithium-ion battery electrodes.

목차 (Table of Contents)

• Abstract iv
• Figure list v
• Table list vii
• 1. Introduction 1
• 1.1 Research Background and Necessity 1
• 1.2 Research Objectives 3
• 1.3 Scope of the Study and Structure of the Thesis 4
• 2. Literature Review 6
• 2.1 Properties of Polyimide (PI) 6
• 2.1.1 Thermal Stability 6
• 2.1.2 Mechanical Properties 6
• 2.1.3 Chemical and Solvent Stability 7
• 2.1.4 Electrical and Surface Properties and Design 7
• 2.2 Comparison of Binders: CMC/SBR, PI, and PVDF – Advantages, Disadvantages, and Trade-offs 8
• 2.2.1 CMC/SBR 8
• 2.2.2 Polyimide (PI) 8
• 2.2.3 PVDF 9
• 2.3 Aqueous/Non-Aqueous Process Routes 10
• 2.3.1 Aqueous Process (CMC/SBR) 10
• 2.3.2 Non-Aqueous Process (PVDF) 11
• 2.3.3 Process Comparison and Selection Criteria 11
• 2.4 In-situ Crosslinking: Concept and Expected Effects 12
• 2.4.1 Concept 12
• 2.4.2 Representative Reaction Examples 12
• 2.4.3 Process Considerations 13
• 2.4.4 Expected Effects 13
• 2.4.5 Limitations and Design Principles 13
• 3. Problem Definition and Hypothesis 15
• 3.1 Problem Definition: The Trade-off Between Adhesion, Resistance, and Thermal Budget 15
• 3.2 Hypothesis Setting (H1–H5) 16
• 4. Experiment Design Overview 18
• 4.1 Materials 18
• 4.2 Electrode Manufacturing 18
• 4.2.1 Slurry Preparation 18
• 4.2.2 Electrode Drying and Imidization 19
• 4.3 2032 Coin Half Cell Manufacturing 20
• 4.4 Variables and Levels 21
• 4.5 Measurement Items 21
• 4.5.1 Peel Test 21
• 4.5.2 Resistance Test 22
• 4.5.3 NMR 22
• 4.5.4 FTIR-ATR 22
• 4.5.5 Electrochemical Properties 22
• 4.5.6 Impedance (EIS) 23
• 5. Electrode Composition Optimization Using DOE 24
• 5.1 Design Method: Taguchi Method and Regression Analysis 24
• 5.2 Response Variables 26
• 5.2.1 Taguchi Analysis: Adhesive Strength 26
• 5.2.2 Regression Analysis: Adhesion Strength 29
• 5.2.3 Taguchi Analysis: Initial Coulombic Efficiency (ICE) 31
• 5.2.4 Regression Analysis: Initial Coulombic Efficiency (ICE) 33
• 5.2.5 Taguchi Analysis: 100-Cycle Capacity Retention 35
• 5.2.6 Regression Analysis: Capacity Retention at 100 Cycles 37
• 5.2.7 Conclusion 39
• 5.3 Factor Influence and Optimal Combination 40
• 6. Comparison of PI Water-Based vs Non-Water-Based Binders 42
• 6.1 NMP-PI vs. Water-Based PI (TEA/DMIZ) Synthesis 42
• 6.2 1H NMR Analysis 44
• 6.3 FTIR-ATR Analysis 45
• 6.4 Adhesion Test (180° Peel Test) 46
• 6.5 Resistance Test 47
• 6.6 Electrochemical Properties 47
• 7. Crosslinked PAmA-DMIZ 52
• 7.1 Water-Based DMIZ Precursor + In-Situ Crosslinking Conditions 52
• 7.2 FTIR-ATR Analysis 54
• 7.3 Adhesion Test (180° Peel Test) 57
• 7.4 Resistance Test 59
• 7.5 Electrochemical Properties 60
• 7.5.1 Voltage Profile 60
• 7.5.2 ICE 61
• 7.5.3 Cyclic Performance 62
• 7.5.4 Rate Capability 64
• 7.5.5 EIS 65
• 8. Crosslinked PAmA-TEA 68
• 8.1 Water-based TEA Precursor + In-situ Crosslinking Conditions 68
• 8.2 Adhesion Test (180° Peel Test) 68
• 8.3 Resistance Test 70
• 8.4 Electrochemical Properties 71
• 8.5 EIS 72
• 9. Comparative Evaluation with Conventional CMC/SBR Binder Systems 75
• 9.1 Comparison Strategy and Rationale 75
• 9.2 Adhesion and Mechanical Response: CMC/SBR vs. Crosslinked PI 76
• 9.3 Electrode Resistance Characteristics of CMC/SBR and PI-Based Binder Systems 77
• 9.4 Electrochemical Stability under Cycling: CMC/SBR vs. PI-Based Binders 79
• 9.5 Electrochemical Impedance Characteristics of PI-Based and CMC/SBR binder Systems 81
• 10. Conclusion 83
• 11. Reference 86