Title Page
Abstract
Contents
Chapter 1. Introduction 15
1.1. Nondestructive and in situ analysis for supercapacitors and lithium-ion batteries 16
1.2. References 19
Chapter 2. Nondestructive analysis of electrode surface degradation in supercapacitors during high-temperature storage 24
2.1. Introduction 25
2.2. Experimental 28
2.3. Results and discussion 30
2.3.1. Storage performance of cylindrical SCs at elevated temperatures 30
2.3.2. Electrolyte decomposition in cylindrical SCs 33
2.3.3. Electrolyte evaporation in cylindrical SCs 36
2.3.4. Change of impedance components after the storage 39
2.3.5. Analysis of degradation mechanism in discharged SCs 43
2.3.6. Specific surface area of active materials 46
2.3.7. Suppression of Rct increase by glutaronitrile[이미지참조] 50
2.4. Conclusions 53
2.5. References 54
Chapter 3. Formation of solid-electrolyte interface of lithium-ion batteries analyzed by in situ FT-IR 61
3.1. Introduction 62
3.2. Experimental 65
3.3. Results and discussion 69
3.3.1. Electrochemical behaviors of ICEMA in PC-based electrolytes 69
3.3.2. Improvement in cell performances of PC-based electrolytes 73
3.3.3. Resistance parameters analysis by EIS fitting 78
3.3.4. Reaction mechanism of PC with ICEMA by in situ FT-IR 84
3.3.5. Verification of PC-based SEI components by ex situ XPS 92
3.3.6. Advanced in situ FT-IR cell to detect SEI components 95
3.3.7. SEI properties depend on electrolyte compositions 98
3.4. Conclusions 101
3.5. References 103
Chapter 4. Conclusions 112
Appendices 115
Appendix A. Supporting information for Chapter 2 115
Appendix B. Supporting information for Chapter 3 118
국문초록 125
Fig. 2.1. Relative values of (a) discharge capacitance and (b) internal resistance of cylindrical SCs depending on storage time at 85 °C according to... 31
Fig. 2.2. CV data of 1.0 M SBPBF₄ in ACN, on three-electrode pouch SCs (a) at 25 °C and (b) at 85 °C (reduction: 0 V to -2.0 V, oxidation: 0 V to +1.5 V).... 34
Fig. 2.3. Weight loss of cylindrical SCs stored at 85 °C. y1 is weight loss according to ACN volatilization and y2 is the changed salt concentration... 37
Fig. 2.4. (a) EIS plots of cylindrical SCs at 0 V before and after storage at 85 °C according to SBPBF₄ concentration and storage state with the equivalent... 40
Fig. 2.5. Rct analysis of cylindrical SCs with 1.2 M SBPBF₄ in ACN after 1,000 hours of storage in the discharged state at 95 °C. Each SC was stored (a)...[이미지참조] 44
Fig. 2.6. Illustration of degradation patterns after storage at 85 °C in the charged and discharged states. 47
Fig. 2.7. (a)~(d) FE-SEM images of AC electrodes after storage at 85 °C for 1,000 hours and (e) specific surface area and (f) isotherm of each AC measured... 48
Fig. 2.8. (a) Resistance increase of cylindrical SCs at 85 °C according to solvents concentration in the discharged state and (b) in the charged state. (c)... 51
Fig. 3.1. Schematic diagram of in situ FT-IR cell. 67
Fig. 3.2. LSVs depending on ICEMA concentration, 0 wt% to 3.0 wt% with 1.0 M LiPF₆ PC/DEC (3/7, v/v) in (a) negative and (b) positive direction and... 70
Fig. 3.3. (a) LUMO and HOMO energies of PC and ICEMA and (b) the molecular structure of ICEMA and the charge of each atom. Those were... 71
Fig. 3.4. Electrochemical performances of graphite||NCM full cell depending on ICEMA concentration in 1.0 M LiPF₆ in PC/DEC. (a) The first charge and... 74
Fig. 3.5. (a) The first charge curves of NCM electrode and full cell potential depending on the electrolytes tested in this study and (b)-(f) dQ/dE plots from... 77
Fig. 3.6. (a) Nyquist plots measured at 4.45 V of graphite||NCM full cells depending on ICEMA concentration and equivalent circuit in the inset and (b)... 79
Fig. 3.7. Resistance variance depending on cell potential during the first charge process of full cells (a) with EC-based electrolyte, (b) with PC-based... 81
Fig. 3.8. (a) FT-IR spectra of ICEMA monomer and ICEMA polymer initiated by benzoyl peroxide (BPO) by thermal polymerization. (b) The thermal... 85
Fig. 3.9. In situ FT-IR spectra and their peaks variance at a negative potential (a) with PC-based electrolyte, (b) with ICEMA-added PC-based electrolyte,... 86
Fig. 3.10. Speculative reaction mechanism of SEI formation initiated by ICEMA in PC-based electrolytes. 89
Fig. 3.11. (a) C 1s, (b) N 1s, and (c) O 1s XPS spectra on graphite electrode after forming SEI in EC-based electrolyte and PC-based electrolyte with ICEMA. 93
Fig. 3.12. Images of the advanced version of cells (a) while raising the tip to activate the reaction and (b) while pressing the tip to measure the film of WE... 96
Fig. 3.13. (a)-(b) In situ FT-IR spectra of PC-based electrolyte. (c) The change in in situ peaks from SEI and (d) LSV data depends on electrolyte compositions. 99