Title Page
Contents
ABSTRACT 9
Chapter 1. Introduction 11
1.1. Overview 11
1.2. A strategy for surface modification of sodium cathode 13
Chapter 2. Experimental method 16
2.1. Material synthesis 16
2.1.1. Coprecipitation of Ni₀.₃₃Fe₀.₃₃Mn₀.₃₃C₂O₄ 16
2.1.2. Synthesis of pristine NaNi₀.₃₃Fe₀.₃₃Mn₀.₃₃O₂ 16
2.1.3. Synthesis of Na₃Zr₂Si₂PO₁₂ coated NaNi₀.₃₃Fe₀.₃₃Mn₀.₃₃O₂ using polyacrylic acid 17
2.2. Material characterization 18
2.3. Cell assembly and electrochemical testing 19
Chapter 3. Results and discussion 20
3.1. Coating process and material characterization 20
3.1.1. Na₃Zr₂Si₂PO₁₂ coating process 20
3.1.2. Material characterization 22
3.1.3. Morphological and structural characterization of synthesized cathode materials 27
3.2. Electrochemical performance of Na₃Zr₂Si₂PO₁₂ coated NaNi₀.₃₃Fe₀.₃₃Mn₀.₃₃O₂ cathode materials 30
3.2.1. Cycling performance of Sodium cathode material 30
3.2.2. Rate performance test of sodium cathode material 34
3.2.3. Air & H₂O stability test of sodium cathode material 37
Chapter 4. Conclusion 42
4.1. Conclusion 42
Reference 44
Appendix 51
Abstract (in Korean) 57
〈Figure. 1〉 Schematic illustrations of the preparation of NZSP-coated NNFM using the PAA surface modification method(left),... 22
〈Figure. 2〉 FT-IR spectra of the mixture solutions of PAA-Ethanol and PAA-Ethanol-Zr, Si alkoxide. 24
〈Figure. 3〉 XRD patterns of bulk Na₃Zr₂Si₂PO₁₂ coating material, pristine NNFM and NZSP-x. 26
〈Figure. 4〉 SEM images of (a) pristine NNFM (b) NZSP-2 (c) NZSP-5. TEM images of (d) NZSP-2 (e) NZSP-5. (f) FFT (Fast... 29
〈Figure. 5〉 (a) Initial charge-discharge curves of the pristine NNFM and NZSP-x electrodes at 0.1C-rate in the 2.0-4.0 V (vs. Na/Na⁺).... 31
〈Figure. 6〉 (a) Cycle performances of pristine NNFM and NZSP-2 based on the energy density. (b) Average charge-discharge voltages... 34
〈Figure. 7〉 (a) Rate performance of pristine NNFM and NZSP-2,5 in the voltage ranges of 2.0-4.0 V at 0.1, 0.2, 1, 2, 5, and 10 C.... 36
〈Figure. 8〉 Moisture exposed casting results of (a) pristine NNFM, (b) NZSP-2. Cycle data of (c) before and after moisture exposed... 39
〈Figure. 9〉 (a) Xrd data of moisture exposed pristine NNFM and NZSP-2. (b) XPS spectra of moisture exposed pristine NNFM and... 41