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Title Page

Contents

Abstract 15

Chapter 1. Introduction 17

1. Lithium batteries 17

1.1. Overview of lithium batteries 17

1.2. Operation of lithium batteries 19

2. Materials for lithium batteries 21

3. Solid-state electrolyte membrane 25

3.1. Poly (vinyl alcohol) - based electrolyte membrane 26

3.2. Ionic liquid 28

4. Motivation and outline of this research 30

Chapter 2. Application of nano-conductor imbedded flexible poly(vinyl alcohol)-based hybrid solid electrolyte for high voltage stable solid-state lithium batteries 32

1. Introduction 32

2. Experimental section 37

2.1. Materials 37

2.2. Synthesized process and preparation of HSEs and cathode materials 37

2.3. Materials characterization 38

2.4. Electrochemical property measurements 41

3. Results and Discussion 42

3.1. Morphology of HSE and Li-ion transporting evaluation 42

3.2. Mechanical, adhesive, and thermal properties of HSE 50

3.3. Interfacial resistances and electrochemical window of HSE 55

3.4. Electrochemical investigation of LCO(ALCO)/HSE | HSE | Li cells 59

Chapter 3. Application of multi-functional cathode and flexible poly(vinyl alcohol)-based hybrid solid electrolyte for high performance solid-state lithium-sulfur batteries 62

1. Introduction 62

2. Experimental section 66

2.1. Materials 66

2.2. Synthesis of S@ACNT active material and PDATFSI conductive binder 66

2.3. Synthesis of PVA-g-PCA-80IL-5HTpca HSE 67

2.4. Materials Characterization 67

2.5. Electrochemical measurements 68

3. Results and Discussion 69

3.1. Morphologies and characterizations of S@ACNTs active material and PDATFSI conductive binder 69

3.2. Electrochemical performance of the solid-state lithium-sulfur battery 79

Chapter 4. Application of the force-bearing cathode and multifunctional double-layer hybrid solid electrolyte for high energy and sustainable solid-state lithium-sulfur battery 83

1. Introduction 83

2. Experimental section 86

2.1. Materials 86

2.2. Fabrication of DLHSE 86

2.3. Fabrication of sulfur cathode 87

2.4. Materials Characterization 88

2.5. Electrochemical measurements 89

3. Results and Discussion 90

3.1. Characterization of S@CNT-COOH and PVA-SPALi 90

3.2. Structural characterizations and multifunctional properties of DLHSE 96

3.3. Compatibility of DLHSE with electrode 111

3.4. Electrochemical performance of solid-state LiSB 115

Chapter 5. Future work - applied potential of multifunctional hybrid solid electrolyte in various solid-state metal-sulfur systems 119

1. Introduction 119

2. Experimental section 120

2.1. Materials 120

2.2. Fabrication of DLHSE and sulfur cathode 121

2.3. Electrochemical measurements 121

3. Results and Discussion 122

Chapter 6. Conclusions 127

References 130

논문요약 151

List of Figures

Figure 1-1. (A) Energy density of various secondary batteries[4], (B) applications of LiBs. 18

Figure 1-2. Illustration of (A) configuration[10] and (B) operation of LiBs. 20

Figure 1-3. Representative structures of (A) cathode materials[13, 14] and (B) anode materials. 22

Figure 1-4. Thermal runaway mechanism of liquid electrolyte-based LiBs. 24

Figure 1-5. Hydrogen bonding in PVA and coordination bonding between OH groups and lithium ions. 27

Figure 1-6. Hydrogen bonding in PVA and coordination bonding between OH groups and lithium ions. 29

Figure 2-1. Comparison of (A) cathode | ICE | Li cell, (B) cathode | SPE | Li cell, and (C) cathode/HSE |HSE | Li cell (this work), (D) Li+ conducting mechanism of HTpca-imbedded PVA-g-PCA/IL electrolyte. 36

Figure 2-2. Sample preparation process for adhesion test. 40

Figure 2-3. (A) 1H NMR spectra of PVA-g-PCA, (B) XRD pattern and (C) FT-IR spectra of HTpca nano-conductors, (D) HR-TEM images of HTpca nano-conductors in various magnifications, and (E) surface and... 45

Figure 2-4. (A) The Li+ conductivity of PVA-g-PCA with different feeding ratios of PCA component, Nyquist plots of (B) PVA-g-PCA(10%), (C) PVA-g-PCA(20%), (D) PVA-g-PCA(30 %) with various... 46

Figure 2-5. IL concentration effect of PVA-g-PCA/IL and 5 wt% HTpca-imbedded PVA-g-PCA/IL systems on (a) Li+ conductivity and (b) Li+ transference number at 25 oC, and (c) Li+ conducting mechanisms of... 47

Figure 2-6. (A) DSC curves of PVA, PVA-g-PCA-60IL and PVA-g-PCA-80IL, (B) XRD patterns of PVA-g-PCA with various concentrations of IL. 48

Figure 2-7. Arrhenius plots of temperature dependence of ionic conductivity for PVA-g-PCA-80IL SPE and PVA-g-PCA-80IL-5HTpca HSE. 49

Figure 2-8. (A) The stress-strain curves of PVA-g-PCA/IL SPEs and HTpca-imbedded PVA-g-PCA/IL HSEs, (B) the adhesive strength of cathode systems prepared using PVA-g-PCA/IL and HTpca-imbedded... 53

Figure 2-9. (A) TGA curves of pure PVA, PYR14-TFSI 0.5M LiTFSI IL, PVA-g-PCA-80IL-5HTpca HSE, and PVA-g-PCA-60IL-5HTpca binder, (B) thermal shrinkage of HTpca-doping PVA-g-PCA/IL electrolytes,... 54

Figure 2-10. Interfacial resistance of ALCO | HSE | Li cells prepared using PVDF and PVA-g-PCA-60IL-5HTpca binder (A-1) before activation, (A-2) after 30 days of aging process, voltage profiles of PVA-g-... 58

Figure 2-11. (A) Charge/discharge curves and (B) cycling performance and (C) impedance spectra of LCO| HSE | Li cells at 25 ℃ (0.2 C) and different voltage ranges, (D) charge/discharge profiles of ALCO | HSE... 61

Figure 3-1. Schematic illustration of the designed LiSB combined by multi-functional cathode and flexible HSE. 65

Figure 3-2. (A) SEM images of CNTs, ACNTs, and S@ACNTs, (B) EDS mapping images of ACNTs, (C) TGA curve and EDS mapping images of S@ACNTs. 74

Figure 3-3. (A) ¹H NMR spectra of PDATFSI polymer, (B) FT-IR spectra of PDATFSI material and PDACl precursor. 75

Figure 3-4. (A) Effect of IL concentration on Li+ conductivity of PDATFSI,(B) adhesive strength of cathode material using S@ACNTs and PDATSI binder for aluminum current collector, (C) SEM images, EDS... 76

Figure 3-5. Photos of Li₂S₆ solution (A) before and (B) after 10 min of adsorption test, (C) UV-vis spectrum of (1) 0.05M Li₂S₆ solution, (2) 0.05M Li₂S₆ solution with S@ACNTs/PDATFSI adsorbent, (3) 0.05M Li₂S₆... 77

Figure 3-6. S 2p XPS spectra of S@ANCTs/PVDF cathode material (A) before and (B) after adsorption test. 78

Figure 3-7. (A) Charge/discharge curves, (B) rate capacity, (C) cycling performance of S@CNTs/PVDF | HSE | Li cell and S@ACNTs/PDATFSI-60IL | HSE | Li cell, and (D) impedance spectra of S@CNTs/PVDF... 81

Figure 3-8. 3D laser confocal investigation and elemental analysis of cathode surface (A) before activation and (B) after 200 cycles, SEM images of the surface of (C) HSE membrane and (D) Li anode at initial state... 82

Figure 4-1. (A) PXRD patterns and (B) FT-IR spectra of CNT and CNT-COOH, (C) SEM images of CNT, (D) EDS mapping images and (E) TGA curve of S@CNT-COOH active material. 94

Figure 4-2. (A) FT-IR spectra of PVA and cross-linking 70IL@PVA-SPALi, (B) XPS spectrum at Li 1s, S2p, and C 1s of 70IL@PVA-SPALi conductive binder, (C) effect of IL concentration on Li⁺ conductivity of... 95

Figure 4-3. (A) Crystal structure of MOF, (B) N₂ sorption isothermal of MOF at 77 K, (C) XRD profiles of MOF, (D) FT-IR spectra of H₂TCCP and MOF nanosheets, (E) TEM images, (F) AFM... 102

Figure 4-4. TGA curve of MOFIL. 103

Figure 4-5. N₂ adsorption/desorption isothermal at 77K of (A) pristine MOF and (B) MOFIL, pore size distribution of (C) pristine MOF and (B) MOFIL. 104

Figure 4-6. (A) synthesis procedure of DLHSE membrane, (B) SEM image of cross-section and EDS mapping images of DLHSE. 105

Figure 4-7. (A) The stress-strain curve of DLHSE membrane, (B) bending images of DLHSE and 70IL@PVA-SPALi membrane, (C) TGA curves of MOFIL, 70IL@PVA-SPALi, and DLHSE membrane,... 106

Figure 4-8. (A) H-type permeation device with DLHSE membrane and PE separator, (B) UV-vis spectrum of solution after permeation test using DLHSE membrane and PE separator, (C) FT-IR spectra of MOFIL... 107

Figure 4-9. (A) Arrhenius plot of the ionic conductivity of DLHSE, (B) Li+ transference number of DLHSE, (C) the mechanism of fast Li+ transport and uniform Li+ flux achieved in DLHSE. 108

Figure 4-10. (A) Li⁺ conductivity of MOFIL with different loading amounts of IL, (B) S 2s spectra, (C) Zn 2p spectra, (D) F 1s spectra and (E) S 2p spectra of MOFIL. 109

Figure 4-11. Current-time plots and impedance spectra before and after polarization of (A) MOFIL, (B) 70IL@PVA-SPALi. 110

Figure 4-12. Interfacial resistance of cathode | DLHSE cells using PVDF and 70IL@PVA-SPALi binder (A-1) before activation and (A-2) after 30 days of the aging process, voltage profile of DLHSE with Li⁺... 113

Figure 4-13. LSV profile of DLHSE membrane. 114

Figure 4-14. (A) Charged/discharged curves, (B) rate capacity, (C) cycling performance of S@CNT-COOH/70IL@PVA-SPALi | DLHSE | Li cell and S@CNT/PVDF | PE(LE) | Li cell, (D) impedance spectra... 117

Figure 4-15. (A) Cycling performance of S@CNT-COOH/70IL@PVA-SPALi | DLHSE | Li cell, S@CNT-COOH/70IL@PVA-SPALi | PE(LE) | Li cell, S@CNT-COOH/PVDF | PE(LE) | Li and S@CNT/PVDF |... 118

Figure 5-1. (A) Zn²⁺ ion conductivity, (B) Zn²⁺ transference number, (C) LSV profile of DLHSE, (D) voltage profile of DLHSE with Zn²⁺ symmetric cells during Zn plating/stripping process at current densities... 125

Figure 5-2. (A) CV profiles, (B) Charged/discharged curves, (C) rate capacity, (D) cycling performance of S@CNT-COOH/70IL@PVA-SPALi | DLHSE | Zn cell and S@CNT/PVDF | PE(1M Zn(TFSI)₂ aq) | Zn cell. 126

초록보기

 하이브리드 고체 전해질(HSE)은 고체 상태의 우수성과 함께 기존의 리튬 이차 전지의 액체 전해질을 대체할 수 있는 잠재력을 가집니다. 폴리 비닐알코올(PVA)은 높은 유전 상수, 좋은 기계적 물성 및 원가경쟁력을 포함하는 탁월한 특성으로 인해 고체 전해질막에 적합한 호스트 고분자 소재로 여겨집니다. 본 연구에선, PVA 를 리튬 금속 전지의 고체전해질로 적용하고자 이온성 액체(IL) 및 무기 필러를 사용하여 이온 전도 소재로 활용하였습니다.

본 연구는 고성능 전고체 리튬 이차전지의 혁신적인 설계를 제안하며, 특히 리튬이온 및 리튬 황 배터리 시스템에 집중하였습니다. 첫 번째로, 폴리(비닐알코올)-g-피롤-2-카복실산(PVA-g-PCA)과 피롤-2-카복실산 기반의 변형된 하이드로탈사이트 (HTpca) 나노 전도체로 구성된 HSE 와 Al₂O₃ 코팅된 LiCoO₂ 활물질을 포함하는 고전압 리튬 이온 배터리 시스템을 제시하였습니다. 해당 HSE 는 뛰어난 Li+ 전도성, Li+ 전달율 및 안정성을 나타냄으로써 높은 비 용량과 장수명 안정성을 가지는 전고체 리튬 금속 배터리를 확보합니다.

두 번째로, 다기능성 양극과 황을 함유한 Al₂O₃ 변형 탄소 나노튜브(S@ACNTs), 그리고 유연한 HSE 를 복합 적용한 고체 리튬-황 배터리 시스템을 제안하였습니다. 우수한 Li+ 전도성, 열안정성, 접착 강도, 불연성 및 유연성을 보유한 폴리 양이온 바인더로서 폴리(다이알릴 디메틸암모늄 비스(트리플루오로 메틸설포닐) 이미드)(PDATFSI)를 적용한 배터리 시스템은 효과적인 다황화물 포집 거동으로 높은 방전 용량과 수명 안정성을 가집니다.

세 번째로, 황이 탑재된 카르복실화 탄소 나노튜브(S@CNT-COOH)와 전도성 바인더로서 이온성 액체를 담은 5-설포 이소프탈산 모노 리튬 고정 폴리 비닐알코올(IL@PVA-SPALi), 그리고 힘 베어링 음극을 복합 적용하여 고성능 고체 리튬-황 배터리의 차세대 모델을 제안하였습니다. 이 시스템은 효과적인 다황화물 차단 및 리튬 수지상 결정 억제를 위해 다기능 이중 층 하이브리드 고체 전해질(DLHSE)을 포함하고 있습니다. 해당 설계를 통해 조립된 LiSB 는 높은 방전 비 용량과 장기적인 주기 안정성을 확보하였습니다.

해당 연구는 제안한 모델을 고체 Zn-S 배터리에 적용함으로써 수계 전해질을 적용한 시스템 대비 우수한 전기화학적 특성을 반영한다고 결론 내렸습니다. 이러한 긍정적인 결과는 개발한 모델이 향후 다른 금속-황 배터리 시스템에 적용될 가능성이 있음을 시사합니다.

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