High-Performance Silicon Anodes Enabled by Free-HF Synthesized Single-Layer MXene through Homogeneous Composite Engineering

국문 초록 (Abstract)

본 연구는 구조적 보존성이 유지된 Free-HF 합성 MXene 이 Si 기반 복합 전극의 전기화학적 성능 향상에 결정적인 역할을 함을 규명하였다. Free-HF 공정으로 제조된 MXene 은 층상 구조가 온전히 유지되고 표면 종단기가 더 잘 노출되는 반면, 일반적인 HF에칭 MXene 은 부분적 층 붕괴와 재응집이 발생하여 구조적 열화가 나타난다. 이러한 FreeHF MXene 을 액상 혼합 방식으로 Si 와 결합하면, Si 입자와의 균일하고 밀착된 인터페이스가 형성되어 전도성 네트워크 구축과 Si 부피 팽창 완화에 효과적으로 기여한다. 이로 인해 SEEMX 전극은 낮은 분극, 안정적인 lithiation/delithiation 거동, 우수한 레이트 특성 및 장기 사이클 안정성을 나타낸다. EIS 및 저항 분석 결과, Free-HF MXene 이 모든 전극 중 가장 낮은 전자 및 계면 저항을 제공함을 확인하였다. 또한 TGA 분석에서는 보존된 MXene 다층 구조가 열적 장벽으로 작용해 고온에서의 Si 산화를 억제함을 확인하였다. 다만, 과도한 MXene 함량은 이온 이동을 저해하여 전기화학적 활성을 감소시키므로 최적 로딩이 필요함을 시사한다. 종합적으로, 본 연구는 Free-HF MXene 이 고성능 Si 음극 개발을 위한 효과적이며 확장 가능한 설계 전략임을 제시한다.

다국어 초록 (Multilingual Abstract)

This study underscores the substantial impact of structurally intact Free-HF-synthesized MXenes on the electrochemical performance of silicon-based composite anodes. In contrast to conventional HF-etched MXenes, which frequently experience partial layer collapse, loss of functional terminations, and reaggregation, the Free-HF method produces MXenes with preserved lamellar structures and highly accessible surface terminations. When incorporated through liquid mixing, intact MXenes establish continuous and close interfacial contact with silicon, forming efficient electron-transport networks and effectively mitigating silicon volume changes during cycling. Consequently, SEEMX electrodes exhibit reduced polarization, stable lithiation/delithiation profiles, significantly enhanced rate capability, and long-term cycling stability. EIS and resistivity tests confirmed that Free-HF MXene provided the lowest electronic and interfacial resistances among all the electrode compositions. Furthermore, the TGA results demonstrate that the preserved multilayer structure functions as a thermal barrier, preventing high-temperature silicon oxidation. However, an excessive amount of MXene can result in ion transport limitations and diminished electrochemical activity, highlighting the necessity of optimizing the MXene content. Overall, these findings establish structurally preserved Free-HF MXene as a highly effective and scalable design approach for next-generation high-performance silicon anodes.

목차 (Table of Contents)

• Abstract in Korean ⅰ
• Abstract in English ⅱ
• Table of Contents ⅲ
• List of figures v
• Chapter 1 Introduction 1
• 1.1. Background and motivation 1
• 1.2. Mxene: Structure, Properties and Opportunities for Si Anode 2
• Chapter 2 Challenges and Motivation for Free-HF MXene-Si Composite Anodes 4
• 2.1. Limitations of Conventional HF-Based MXene Synthesis 4
• 2.2. Necessity of Free-HF/Fluoride-Free MXene Synthesis 4
• 2.3. Emergence of MXene-Silicon Composite Anodes and Remaining Challenges 5
• 2.4. Research Objectives 5
• Chapter 3 Experiments 7
• 3.1. Materials 7
• 3.2. Synthesis of Free-HF MXene 7
• 3.3. Preparation of Si-Based Composite Electrodes 13
• 3.3.1. Ball milling 13
• 3.3.2 Liquid mixing 13
• 3.3.3. Si-Super P, and Si-CNT 14
• 3.4. Assembling Half Coin cell 14
• 3.5. Materials and Electrochemical Characterization 14
• 3.6. Mechanical Performance 15
• Chapter 4 Results and Discussion 16
• 4.1. Materials Characterization 16
• 4.1.1 X-RAY Diffraction (XRD) 16
• 4.1.2. Thermogravimetric Analysis (TGA) 18
• 4.1.3. Transmission Electron Microscope (TEM) 20
• 4.1.4 EDS Mapping 24
• 4.1.5. X-ray Photon Spectroscopy (XPS) 27
• 4.2 Mechanical Performances 29
• 4.3. Electrochemical Performance 31
• 4.3.1. Cycling and Rate Capability Measurement of Baseline Conductive Materials 31
• 4.3.2. Voltage-Capacity profiles of Baseline Conductive Material 33
• 4.3.3. Cycling and Rate Capability Measurement of Mxene Electrodes 35
• 4.3.4. Electrochemical Impedance Spectroscopy (EIS) AND Cyclic Voltammetry (CV) of Baseline Conductive Materials 36
• 4.3.5. Electrochemical Impedance Spectroscopy of Mxene Electrodes 41
• 4.3.6. Electrical characteristics 43
• 4.3.7. Trade-off between Electronic Conductivity and Li+ Transport in High-Mxene Loading Electrodes45
• 4.4. Morphology analysis of the electrode film 47
• 4.4.1. Surface and Cross-section SEM Before/After 200 cycles 47
• Conclusion 50
• Reference 51