나트륨 이온 전지의 구조적·사이클링 안정성 향상을 위한 프러시안 화이트 양극의 Ni과 Fe 공동 도핑 비율 제어 = Tailoring Ni and Fe co−doping ratios in Prussian white cathodes for enhanced structural and cycling stability of sodium−ion batteries

다국어 초록 (Multilingual Abstract)

In this study, Ni and Fe co−doping was employed to enhance the structural stability and electrochemical performance of manganese−based Prussian white (MHCF). Manganese−based Prussian white has attracted considerable attention as a promising cathode material for next−generation sodium−ion batteries due to its high energy density, low cost, high operating voltage, and simple synthesis process. However, it suffers from rapid performance degradation and shortened cycle life resulting from low structural stability caused by the Jahn−Teller effect. To address this issue, the effects of Ni and Fe co−doping on the structural stability of MHCF and the specific roles of each dopant element were systematically analyzed. Among the various co−doping ratios examined, the MNFHCF−631 with a Mn:Ni:Fe ratio of 6:3:1 exhibited the best electrochemical performance, achieving a high−capacity retention of 96.30% after 100 cycles at a current rate of 0.2C, as well as superior rate capability. These results demonstrate that Ni, an electrochemically inactive transition metal, enhances structural stability, while Fe, an electrochemically active transition metal, compensates for the capacity loss induced by Ni’s inactivity through its additional capacity contribution. Consequently, the synergistic effects of Ni and Fe co−doping lead to enhanced structural stability and improved electrochemical performance.

목차 (Table of Contents)

• Abstract ⅲ
• List of Figures ⅳ
• List of Tables ⅵ
• 1. Introduction 1
• 1.1. Explanation of sodium−ion battery 1
• 1.2. Types of cathode materials for sodium-ion batteries 4
• 1.2.1 Layered oxides cathode material 4
• 1.2.2 Prussian blue analogues (PBAs) cathode material 6
• 1.2.3 Polyanion compounds cathode material 8
• 2. Literature survey 10
• 3. Purpose of this work 13
• 4. Experimental 14
• 4.1. Chemicals and Regents 14
• 4.2. Synthesis of MNFHCF 14
• 4.3. Material characterization 16
• 4.4. Electrochemical measurement 16
• 5. Result and Discussion 18
• 5.1. Morphology and Characterization 18
• 5.1.1. FESEM 18
• 5.1.2. TEM 22
• 5.1.3. XRD 28
• 5.1.4. Raman 30
• 5.1.5. FTIR 32
• 5.1.6. TGA 34
• 5.1.7. XPS 36
• 5.2. Electrochemical characterization 41
• 5.2.1. Charge/Discharge Test 41
• 5.2.2. EIS 47
• 5.2.3. Cyclic voltammetry (CV) 50
• 5.3. Post cycling analysis 52
• 5.3.1. XRD 52
• 5.3.2. FESEM 54
• 5.3.3. EIS 56
• 5.3.4. Cyclic voltammetry (CV) 59
• 5.4. Mechanisms 61
• 6. Conclusion 63
• 7. References 64