Title Page
Contents
ABSTRACT 9
Ⅰ. Introduction 11
1.1. The Background of Supercapacitors 11
1.2. The Basic Theory and Principles of Supercapacitors and Applications 13
1.2.1. Theory of Electric Double Layer 13
1.2.2. Pseudocapacitor 15
1.2.3. Asymmetric Hybrid Supercapacitor 16
1.3. Electrochemical Parameters of the Performance of Supercapacitor 17
Ⅱ. Experimental Method 19
2.1. Materials and Chemicals 19
2.2. Process of Synthesizing the NCF-S@CoPi on NF. 20
2.2.1. Synthesis of NiCoFe-LDH (NCF-LDH) and NiCoFe-S (NCF-S) 20
2.2.2. Preparation of NiCoFe-S@Cobalt phosphate (NCF-S@CoPi) as Electrodeposition. 21
2.2.3. Fabrication of Asymmetric Hybrid Supercapacitor (AHSC) 22
Ⅲ. Characterization Method 23
3.1. Material Characterization 23
3.2. Electrochemical Characterization 24
Ⅳ. Results and Discussion 25
4.1. Morphology, Structure, and Chemical Characterization of NCF-S@CoPi 25
4.2. Electrochemical Charactecization 40
4.2.1. Electrochemical Performance of NCF-S@CoPi 40
4.2.2. Electrochemical Performance of Asymmetric Hybrid Supercapacitor (AHSC) 53
Ⅴ. Conclusions 61
References 62
Appendix 73
Abstract (in Korean) 74
Table 4-1. Comparison of specific surface area, average pore size, and total pore volume calculated through BET and BJH analysis. 34
Table 4-2. Comparison of Rs and Rct. 44
Table 4-3. Comparison specific capacitance with different electrode at different condition 47
Table 4-4. Comparison energy density and power density with previous reported supercapacitor electrode. 59
Figure 1-1. Schematic image of (a) electrical double layer capacitor (EDLC) and (b) pseudocapacitor. 12
Figure 1-2. The electric double layer model of (a) Helmholtz model, (b) Goucy- Chapman model, and (c) Stern model. 14
Figure 4-1. Synthesis process of NCF-S@CoPi. 26
Figure 4-2. Photograph of NCF-LDH, NCF-S, and NCF-S@CoPi. 27
Figure 4-3. FE-SEM image of (a) NCF-LDH, (b) NCF-S, and (c)NCF-S@CoPi 28
Figure 4-4. EDS mapping derived from FE-TEM image of (a) NCF-LDH, (b) NCF-S, and (c) NCF-S@CoPi. 29
Figure 4-5. (a) XRD pattern and (b) FT-IR spectrum of NCF-LDH, NCF-S, and NCF- S@CoPi, and high-resolution FE-TEM image and (c) NCF-LDH, (d) NCF-S, and (e)... 32
Figure 4-6. (a) N₂ adsorption-desorption isotherms and (b) sized distribution of NCF- LDH, NCF-S, and NCF-S@CoPi. 33
Figure 4-7. XPS survey of NCF-LDH, NCF-S, and NCF-S@CoPi. 37
Figure 4-8. XPS spectra of NCF-LDH, NCF-S, and NCF-S@CoPi for (a) O 1s, (b) Ni 2p, and (c) Fe 2p spectrum. 38
Figure 4-9. XPS spectra of NCF-LDH, NCF-S, and NCF-S@CoPi for (a) Co 2p, (b) S 2p, and (c) P 2p spectrum. 39
Figure 4-10. (a) CV curves and (b) GCD curves of NCF-LDH, NCF-S, and NCF- S@CoPi at 5 mV s⁻¹ and 4 mA cm⁻², (c) CV curves and (d) GCD curves of NCF-... 42
Figure 4-11. Equivalent circuit of supercapacitor electrode. 43
Figure 4-12. Comparison specific capacitance with different deposition time. 46
Figure 4-13. The long-term stability of NCF-S@CoPi at 100 mA cm⁻² 48
Figure 4-14. (a) FE-SEM and (b) XRD pattern comparison with before and after long- term cyclic test (long term stability). 49
Figure 4-15. (a) The relationship between logarithmic diagrams of current and scan rates 1~8 mV s⁻¹, and (b) capacitance-diffusion distribution of NCF-S@CoPi in... 51
Figure 4-16. CV curves and calculated diffusion-controlled region of supercapacitor with different scan rate (a)~(f) 8 mV s-1 to 0.8 mV s⁻¹. 52
Figure 4-17. Schematic image of asymmetric hybrid supercapacitor cell NCF- S@CoPi//AC with PVA/KOH electrolyte. 54
Figure 4-18. (a) CV curve, (b) GCD curve of AC/NF negative electrode, CV curves of AC and NCF-S@CoPi, and (b) CV curves of AHSC with different potential windows. 55
Figure 4-19. (a) CV and (c) GCD curve of AC//NCF-S@CoPi HSC cell, (d) Capcitance Retention of different current density, and (e) Nyquist plot of NCF-S@CoPi. 57
Figure 4-20. (a)Long term stability of PVA-KOH hybrid supercapacitor and columbic efficiency at 100 mA cm⁻², (b) Ragone plot with various supercapacitor and (c)... 60