표제지

국문초록

목차

제1장 서론 (Introduction) 13

1.1. Introduction of LIB 13

1.1.1. Needs for LIB development 13

1.1.2. LIB component 14

1.2. Development of high energy density cathode material 15

1.2.1. Conventional cathode material (LiCoO₂) 15

1.2.2. Ni-rich NCM cathode material (LiNixCoyMnzO2, x+y+z＝1)[이미지참조] 17

1.3. Problems of Ni-rich NCM cathode material 18

1.3.1. Thermal instability during calcination process 18

1.3.2. Degradation of Ni-rich NCM cathode material due to Ni4+ instability[이미지참조] 20

1.3.3. Transition metal dissolution due to HF 24

1.3.4. Reasons of the Ni-rich NCM cathode material degradation 24

1.4. Technology to improvement Ni-rich NCM cathode material 25

1.4.1. Enhance internal stability of Ni-rich NCM cathode material (Doping tech.) 26

1.4.2. Enhance surface stability of Ni-rich NCM cathode material 27

1.4.3. Additive technology enhancing surface stability 28

1.4.4. Coating technology enhancing surface stability 31

제2장 Ni-rich NCM surface modification with allyl phenyl sulfone additive 37

2.1. Introduction 37

2.2. Result and discussion 39

2.2.1. Chemical property analysis of APS additive 39

2.2.2. Electrochemical property of APS additive 40

2.2.3. Electrolyte decompositions analysis of APS additive 43

2.2.4. Chemical reactivity of APS additive 47

2.2.5. Applicability evaluation of APS additive 49

2.3. Conclusion 50

제3장 Enhanced Ni-rich NCM surface stability by 1H,1H,2H,2H-perfluorooctyltriethoxysilane-formed multifunctional CEI 53

3.1. Introduction 53

3.2. Result and discussion 55

3.2.1. Surface analyses of POS coating 55

3.2.2. Electrochemical analyses of POS coating 57

3.2.3. Electrolyte decomposition analyses of POS coating 64

3.3. Conclusion 68

제4장 Reference 70

제5장 Experimental 83

5. General experimental process 83

5.1.1. Manufacturing process of electrolyte and cathode using APS 83

5.1.2. Assembling and manufacturing cell condition using APS 83

5.1.3. Analysis process using APS 84

5.2.1. Manufacturing process of cathode using POS 84

5.2.2. Assembling and manufacturing cell condition using POS 85

5.2.3. Analysis process using POS 86

ABSTRACT 87

Table 1.1. Residual lithium amount according to Ni content of NCM. 19

Table 1.2. Summary of Ni-rich NCM cathode material degradation reasons. 25

Table 3.1. Rietveld refinement value of LN83 58

Figure 1.1. Charge/discharge process of LIB. 14

Figure 1.2. Structure of LCO. 15

Figure 1.3. Phase transition of LCO. 16

Figure 1.4. Characteristic change of Ni, Co, Mn ratio. 17

Figure 1.5. Schematic illustrations of the (a) ordered and (b) disordered phase in NCM. 18

Figure 1.6. Parasitic reaction of residual lithium. 20

Figure 1.7. Formation of electrolyte decomposition product on the surface of NCM. 21

Figure 1.8. Irreversible phase transition from the surface of NCM. 22

Figure 1.9. Analysis of irreversible phase transition by dq dv-1.[이미지참조] 23

Figure 1.10. Degradation of NCM cathode material by microcrack. 23

Figure 1.11. Transition metal dissolution by HF. 24

Figure 1.12. Doping techniques for improvement of NCM thermal stability. 26

Figure 1.13. Schematic illustration of additive techniques and coating techniques. 27

Figure 1.14. Additive techniques for improvement of NCM surface stability. 28

Figure 1.15. Surface analysis (left) and flame retardant effect (right) of diphenyloctyl phosphate. 29

Figure 1.16. Electrochemical performance (top) and surface analysis (down) of fluorophenyl methyl sulfone. 30

Figure 1.17. Coating techniques for improvement of NCM surface stability. 31

Figure 1.18. SEM images of (a) NCM811 and (b) NCM811@LAPO, (c) thermal stability test through DSC curve, (d) electrochemical performance of AlPO₄. 32

Figure 1.19. (a) Chemical equation about residual lithium and precursor, (b) electrochemical performance of lithium complex. 32

Figure 1.20. (a) Surface morphology, (b) electrochemical performance of lithium fluoride, (c), (d) surface resistance analysis through EIS. 33

Figure 1.21. (a) Amount of dissolved transition metal, (b) electrochemical performance of silicon oxide. 34

Figure 2.1. Schematic illustration of APS additive techniques. 37

Figure 2.2. (a) Ionic conductivity of electrolyte and (b) analysis of oxidation potential using LSV. 39

Figure 2.3. (a) Potential profile of the cells at the 2nd cycle at 25 ℃, (b) electrochemical performance of the cells, (c) rate capability of the cells. 40

Figure 2.4. (a) Potential profile of the cell at the 2nd cycle at 45 ℃, (b) electrochemical performance of the cells, (c) average coulombic efficiency, (d) rate capability of the cells. 41

Figure 2.5. Surface analysis of (a), (c) cycled NCM811 and (b), (d) cycled 0.25 APS using SEM and TEM. 44

Figure 2.6. Surface resistance analysis of (a) initial state of NCM811 and (b) cycled state of NCM811. (c) Analysis of chemical component on the cycled NCM811 and 0.25 APS. 45

Figure 2.7. (a) Reaction with APS and TBAF, 1H NMR spectrum of (b) APS, (c) TBAF and (d) APS TBAF solution. 47

Figure 2.8. Mechanism of HF scavenging reaction. 48

Figure 2.9. Amount of dissolved transition metal cycled NCM811 and 0.25 APS. 49

Figure 2.10. (a) Voltage profile of the full cells, (b) electrochemical performance of the full cells. 50

Figure 2.11. Summary of APS additive techniques. 51

Figure 3.1. Schematic illustration of POS coating techniques. 53

Figure 3.2. Schematic illustration of POS diffusion. 54

Figure 3.3. Surface analysis of P-LN83 and POS modified-LN83 by (a) SEM and (b) TEM. (c) analysis of chemical component on the P-LN83 and 1.0 POS-LN83. 56

Figure 3.4. (a) FFT and (b) XRD spectra of P-LN83 and 1.0 POS-LN83. 57

Figure 3.5. Rietveld refinement of (a) P-LN83, (b) 1.0 POS-LN83, (c) 2.0 POS-LN83, (d) 3.0 POS-LN83. 58

Figure 3.6. CV analysis of (a) P-LN83, (b) 1.0 POS-LN83, (c) 2.0 POS-LN83, (d) 3.0 POS-LN83. (e) Linear slope of the maximum current as a function of the square root of scan rate. (f)... 59

Figure 3.7. CV analysis of (a) P-LN83 and (b) 1.0 POS-LN83, (c) Potential profile of LN83 cells, (d) electrochemical performance and initial coulombic efficiency of LN83 cells. 60

Figure 3.8. (a) Potential profile of LN83 cells. (b) electrochemical performance LN83 cells. Lithium diffusion coefficient analized by GITT (c) before cycling and (d) after cycling. 61

Figure 3.9. (a) CA curves P-LN83 and 1.0 POS-LN83. (b) magnified CA curves P-LN83 and 1.0 POS-LN83. 62

Figure 3.10. Internal cell pressure measured by charging process. 63

Figure 3.11. Analysis of (a) P-LN83 and (b) 1.0 POS-LN83 electrochemical reversible by dQ dV-1.[이미지참조] 64

Figure 3.12. Surface analysis of (a), (b) cycled P-LN83 and (c), (d) cycled 1.0 POS-LN83 using SEM and TEM. Surface resistance analysis of (e) initial state of LN83 and (f) cycled state of LN83. 65

Figure 3.13. XPS spectra (a) after formation surface of P-LN83 and 1.0 POS-LN83 and (b) cycled surface of P-LN83 and 1.0 POS-LN83. 67

Figure 3.14. Amount of dissolved transition metal cycled P-LN83 and 1.0 POS-LN83. 68

Figure 3.15. Summary of POS coating techniques. 69