Title Page
Contents
ABSTRACT 11
Ⅰ. Introduction 12
1.1. The Theoretical Background and Evaluating Parameters of Supercapacitors 12
1.1.1. The Theoretical Background of Supercapacitors 12
1.1.2. The Electrochemical Parameters for Evaluating the Performance of Supercapacitors 16
1.2. The Research Background of Supercapacitors and Its Application 18
Ⅱ. Experimental Method 22
2.1. Materials and Chemicals 22
2.2. Sequence of Synthesizing NiCoS@NiCoLDH on Ni Foam 23
2.2.1. Synthesis of NiCoS Nanocomposites on Ni Foam 23
2.2.2. Synthesis of NiCoLDH Nanosheets on NiCoS (NiCoS@NiCoLDH) 24
2.2.3. Fabrication of Flexible Asymmetric Supercapacitor Cell (ASC) 25
2.3. Material and Electrochemical Characterization 26
2.3.1. Material Characterization 26
2.3.2. Electrochemical Characterization 27
Ⅲ. Results and Discussion 28
3.1. Material Chracteriazation 28
3.2. Electrochemical characterization 51
3.2.1. Three Electrodes system 51
3.2.2. Two Electrodes system 66
Ⅳ. Conclusion 75
References 76
Appendix 88
Abstract (in Korean) 89
Table 3-1. EDS element analysis of NiCoS and NiCoS@NiCoLDH-40 (corresponding to Figure 3-7). 38
Table 3-2. Surface atomic percent (%) of NiCoS, NiCoLDH-40, and NiCoS@NiCoLDH-40 determined from XPS results (corresponding to Figure 3-10). 46
Table 3-3. BET surface area, pore volume, and average pore diameter of NiCoLDH-40 and NiCoS@NiCoLDH-40. 49
Table 3-4. Calculated electrochemical parameters for the NiCoS@NiCoLDH-40//AC ASC and comparison with previously reported literatures using LDH-based material. 72
Figure 1-1. Ragone plots showing power density versus energy density for various types of energy storage devices. 13
Figure 1-2. Schematic illustration of supercapacitor types: (a) electrochemical double layer (EDLC) and (b) pseudocapacitor. 15
Figure 3-1. Schematic illustration for the fabrication procedure of NiCoS and NiCoLDH on Ni foam via solvothermal and electrodeposition procedures, respectively. 29
Figure 3-2. Digital photographs of (a) NiCoS, (b) NiCoLDH-40, and (c) NiCoS@NiCoLDH-40. 30
Figure 3-3. FE-SEM images of (a-b) NiCoS, (c-d) NiCoLDH-40, and (e-f) NiCoS@NiCoLDH-40. 32
Figure 3-4. (a-d) FE-SEM and (e) EDS mapping images of the scratched NiCoS@NiCoLDH-40. 33
Figure 3-5. (a) Schematic illustration of the synthesis procedure of NiCoLDH on the NiCoS through electrodeposition (inset scale bar: 1 µm). FE-SEM images of (b)... 34
Figure 3-6. FE-TEM images of (a-c) NiCoS and (d-f) NiCoS@NiCoLDH-40 (yellow and blue lines indicate lattice d-spacings of sulfide and hydroxide, respectively). 36
Figure 3-7. EDS mapping images of (a) NiCoS and (b) NiCoS@NiCoLDH-40 confirmed by FE-TEM. 37
Figure 3-8. XRD patterns NiCoS, NiCoLDH-40, and NiCoS@NiCoLDH-40. 40
Figure 3-9. FT-IR spectra of (a) NiCoS, NiCoLDH-40, NiCoS@NiCoLDH-40, and (b) NiCoS@NiCoLDH synthesized with various deposition times of LDH (5-50 min). 42
Figure 3-10. XPS spectra (a) survey scan and the deconvoluted spectra for specific elements of (b) Ni 2p, (c) Co 2p, (d) O 1s, and (e) S 2p for NiCoS, NiCoLDH-40, and... 45
Figure 3-11. (a) N₂ adsorption/desorption isotherm and (b) pore size distribution plot of Ni foam, NiCoLDH-40, and NiCoS@NiCoLDH-40. 48
Figure 3-12. Contact angle photos of the pressed Ni foam samples of (a) NiCoS, (b) NiCoLDH-40, and (c) NiCoS@NiCoLDH-40. 50
Figure 3-13. Comparison of electrochemical performance between NiCoS, NiCoLDH-40, and NiCoS@NiCoLDH-40: (a) CV curves at a scan rate of 20 mV s⁻¹,... 52
Figure 3-14. Comparison of electrochemical performance between NiCoS@NiCoLDH electrodes with different electrodeposition times of LDH: (a) CV... 54
Figure 3-15. (a) CV curves of NiCoS@NiCoLDH-40 at different scan rates from 5 mV s⁻¹ to 50 mV s⁻¹. GCD curves of (b) NiCoS@NiCoLDH-40, (c) NiCoS, and (d)... 56
Figure 3-16. Electrochemical properties of NiCoS@NiCoLDH-40: Capacitive diffusion-controlled contribution to charge storage at different scan rates of (a) 1, (b)... 59
Figure 3-17. Electrochemical properties of NiCoLDH-40: Capacitive diffusion-controlled contribution to charge storage at different scan rates of (a) 1, (b) 0.8, (c)... 60
Figure 3-18. EIS Nyquist plots of (a) NiCoS, NiCoLDH-40, NiCoS@NiCoLDH-40, and (b) NiCoS@NiCoLDH with different electrodeposition times of LDH (inset... 62
Figure 3-19. Cyclic stability and Coulombic efficiency of (a) NiCoS@NiCoLDH-40 and (b) NiCoLDH-40 in 6M KOH solution for 8000 cycles. FE-SEM images of (c)... 64
Figure 3-20. (a) The schematic illustration of the asymmetric supercapacitor configuration. (b-c) Digital photographs of the NiCoS@NiCoLDH-40//AC... 67
Figure 3-21. (a) CV curves of NiCoS@NiCoLDH-40 and activated carbon electrodes performed in a three-electrode system. Electrochemical evaluation of the... 69
Figure 3-22. (a) Ragone plot of NiCoS@NiCoLDH-40//AC asymmetric device and reported LDH-based asymmetric supercapacitors for comparison. (b) Cycling... 71
Figure 3-23. (a) Electrochemical performances of ASC devices in series and parallel circuits: GCD curves of a single device and two ASC devices connected in series and... 74