Title Page
Abstract
Contents
1. Introduction 15
1.1. Transition to the electric vehicle era 15
1.2. Battery diagnostics based on chemical understanding 16
1.3. The chemical indicators identifying heterogeneity inside a cell 18
1.4. References 19
2. Lifetime prediction of lithium ion batteries by using the heterogeneity of graphite anodes 23
2.1. Introduction 23
2.2. Result and discussion 26
2.2.1. Heterogeneity of Gr anodes 26
2.2.2. △PeakS₂ as a key descriptor for electrode heterogeneity[이미지참조] 37
2.2.3. Lifetime prediction of LFP/Gr cells by correlating with △PeakS₂[이미지참조] 41
2.2.4. PeakS₂ as a tool of cell inspection[이미지참조] 46
2.3. Conclusion 52
2.4. Experimental procedures 52
2.5. References 57
3. Entropymetry for detecting micro-cracks in high-nickel layered oxide cathodes 62
3.1. Introduction 62
3.2. Result and discussion 66
3.2.1. Interpretation of △S profiles 66
3.2.2. Structural changes of NCM811 along with the SOC 70
3.2.3. Structural heterogeneity by micro-crack formation 72
3.2.4. Detection of micro-cracks from △S profiles 78
3.2.5. Generalization across the family of high-Ni layered oxides 83
3.3. Conclusion 85
3.4. Experimental procedures 85
3.5. References 89
4. Conclusion 94
초록 96
Table 2.1. Prediction errors of the lifetime prediction models. Training and testing errors of the lifetime prediction models using... 44
Table 2.2. Average and standard deviation of capacity and IR for the cells selected for the middle PeakS₂, similar 1st IR, and similar 1st Q modules.[이미지참조] 51
Table 2.3. Mean and standard deviations of each variable for the dataset of 77 LFP/Gr cells. 55
Figure 1.1. Cumulative EV sales and EV market share. Battery, plug-in hybrid and hydrogen fuel-cell EVs are all included. Adapted from... 15
Figure 1.2. Cell diagnosis and management of LIBs at each step in the life cycle of LIBs. 17
Figure 1.3. Heterogeneity from particle, electrode to cell level in aLIB. (A) Adapted from Tian et al. (B) Ho et al. (C) Senyshyn et al. 19
Figure 2.1. Heterogeneity of Gr anodes and relation to voltage profiles. Scheme showing the relation between spatial homogeneity... 27
Figure 2.2. Voltage (top) and corresponding DV (bottom) profiles of an LFP/Gr cylindrical cell as a function of the capacity during charge... 28
Figure 2.3. DV profiles against the capacity under different cycling conditions: (A) 1C@25 ℃, (B) 2C@25 ℃, (C) 1C@45 ℃, and (D)... 29
Figure 2.4. (A) △PeakS₂ and (B) △PeakS₄ vs. SOH for four different cycling conditions: 1C@25 ℃, 2C@25 ℃, 1C@45 ℃, and 1C@10 ℃.[이미지참조] 30
Figure 2.5. △PeakS₄ is defined. Same voltage (top) and DV (bottom) profiles of the LFP/Gr cylindrical cell shown in Figure 2. 2.[이미지참조] 31
Figure 2.6. DV vs. capacity profiles during discharge under different cycling conditions: (A) 1C@25 ℃ and (B) 2C@25 ℃. 31
Figure 2.7. SEM and optical (center) images of the Gr anodes of a fresh unrolled LFP/Gr cell. "Inside" and "outside" refer to the side... 32
Figure 2.8. SEM and optical (center) images of the Gr anodes of an LFP/Gr cell cycled at 1C@ 25 ℃ until SOH80 was reached. "Inside"... 33
Figure 2.9. SEM and optical (center) images of the Gr anodes of LFP/Gr cell cycled at 2C@ 25 ℃ until SOH80 was reached. "Inside"... 34
Figure 2.10. TOF-SIMS results of the Gr anodes in the LFP/Gr cells (A) before cycling (SOH100), and after cycling at (B) 1C@25 ℃ and... 35
Figure 2.11. DMC solvent used for washing the jellyrolls of LFP/Gr cells: (A) before cycling and after cycling (SOH80) at (B) 1C@25 ℃... 36
Figure 2.12. Correlation between electrode heterogeneity and cycle life. (A) DV profiles of homogeneous and heterogeneous cells, and... 37
Figure 2.13. Correlation between electrode heterogeneity and electrode arrangement of LFP/Gr cylindrical cells. (A) Side cross-... 38
Figure 2.14. Vertical cross-sectional XRM images of the (A) homogeneous and (B) heterogeneous LFP/Gr cylindrical cells. 39
Figure 2.15. MCC method for calculation of the roundness about the enlarged void at the core of the jellyrolls in the (A) homogeneous... 41
Figure 2.16. Correlation between the life cycle and PeakS₂ intensity. (A) Cycling retention profiles and (B) differential voltage profiles of...[이미지참조] 42
Figure 2.17. Cycle life vs. △PeakS₂ intensity plot with correlation coefficient of 0.75.[이미지참조] 43
Figure 2.18. Comparison of RMSE values during 1000 iterations between the dummy regressor and (A) PeakS₂ intensity, (B) PeakS₄...[이미지참조] 45
Figure 2.19. Correlation of cycle life with (A) PeakS₄ intensity, (B) 1st IR, (C) 1st Q, and (D) Var (△Q₁₀₀-₁₀(V)).[이미지참조] 46
Figure 2.20. PeakS₂-based diagnosis for module assembly. Using PeakS₂ for the high-quality inspection of as-manufactured cells for...[이미지참조] 47
Figure 2.21. Module construction according to cell classification based on the PeakS₂ intensity. (A) Box plots of cycle life vs. PeakS₂...[이미지참조] 49
Figure 2.22. (A) Capacity distributions of six cells in each module group classified based on similar capacity (orange) and middle PeakS₂...[이미지참조] 50
Figure 2.23. (A) Deviation of PeakS₂ intensity vs. deviation of capacity decay of individual cells in different modules. (B) Box plots...[이미지참조] 51
Figure 3.1. (A) △S (black) and dQ dV¯¹ (blue) profiles of NCM811 along the open circuit voltage (OCV) landscape. (B) Schematic... 67
Figure 3.2. (A) Comparison of calculated and measured △S of NCM811 as a function of the voltage. (B) Peak deconvolution of the... 69
Figure 3.3. (A) Evolution of the in-situ XRD profiles around the (003) and (110) peaks during the first charging of NCM811 after... 71
Figure 3.4. Cross-sectional SEM images of NCM811 particles (A) after precycle and at 101th cycle at 60 ℃ with upper cut-off of (B)...[이미지참조] 73
Figure 3.5. Voltage profiles at the 2nd and 100th cycles for NCM811 half-cells with cut-off voltages of (A) 4.1 V and (B) 4.3 V with...[이미지참조] 74
Figure 3.6. (A) STEM image and (B) EELS analysis of NCM811 particles after 100 cycles at 60 ℃ with upper cut-off of 4.3 V. EELS... 75
Figure 3.7. Cycling performance of four NCM811 cells for 50 or 100 cycles at 60 ℃ with cut-off potentials of 4.1 or 4.3 V, respectively. 78
Figure 3.8. (A) Changes in the integral breadth (integrated intensity/maximum intensity of the highest peak) based on analyses... 79
Figure 3.9. Multiple measurements of △S for the half-cells of NCM811 after (A) 50 cycles with cut-off of 4.1 V, (B) 50 cycles... 80
Figure 3.10. Relative diffusivity vs. SOC for NCM811 cathode as measured via GITT analysis after 100 cycles at 60 ℃ with different... 81
Figure 3.11. Schematic comparison between homogeneous and heterogeneous lithiation of an NCM811 particle before and after... 82
Figure 3.12. Cross-sectional SEM images of (A) NCM622 and (B) LiNiO₂ particles after 100 cycles at 60 ℃ with upper cut-off of 4.3... 83
Figure 3.13. Measurement of the entropy changes of batteries by monitoring variations in the OCV upon temperature variations.... 88
Figure 3.14. Verification of the reproducibility of △S measurements for different cells containing precycled NCM811 cathodes. 88