Title Page
Contents
ABSTRACT 16
Chapter 1. Introduction 19
1.1. Background 19
1.2. High-performance lithium-ion battery separator 22
1.2.1. High tensile strength separator for lithium-ion battery 25
1.2.2. High porosity separator for lithium-ion battery 27
1.3. Battery internal temperature prediction 33
1.3.1. Conventional methods predict internal battery temperature 34
1.3.2. Advanced sensing technology predicts internal battery temperature 37
1.4. Research content 40
1.5. Thesis outline 42
Chapter 2. Electrospinning and electrochemical impedance spectroscopy theory 44
2.1. Electrospinning theory 44
2.1.1. Basic principle of electrospinning 44
2.1.2. Electrospinning device and spinning process 45
2.2. Electrochemical impedance spectroscopy theory 45
Chapter 3. Experimental setup and characterization methods 50
3.1. Experimental materials 50
3.2. Sample preparation 50
3.2.1. Preparation of separator PAN/PVP/PVDF(HFP) 50
3.2.2. Preparation of high porosity separator PAN/PVP/PVDF(HFP) 51
3.2.3. Preparation of high tensile strength separator PAN/PVP/PVDF(HFP) 52
3.2.4. Preparation of high-performance separator PAN/PVP/PVDF(HFP) 52
3.2.5. Assemble lithium-ion batteries 53
3.3. Material testing and characterization 54
3.3.1. Scanning Electron Microscope (SEM) 54
3.3.2. Transmission Electron Microscope (TEM) 54
3.3.3. Fourier transform infrared spectroscopy (FTIR) 55
3.3.4. Thermogravimetric analysis (TGA) 55
3.3.5. Porosity 56
3.3.6. Electrolyte uptake 57
3.3.7. Mechanical properties 58
3.3.8. Thermal shrinkage test 59
3.3.9. Ionic conductivity 59
3.3.10. Li⁺ transference number 60
3.3.11. Battery charging and discharging performance 61
Chapter 4. High porosity and high tensile strength separator by post-treatment 62
4.1. High porosity separator after hydrolysis 62
4.1.1. Characterization 62
4.2. High tensile strength separator after heat treatment 65
4.2.1. Characterization 66
4.3. Concluding remarks 70
Chapter 5. High-performance electrospun separator for lithium-ion battery based on dual-hybridizing of materials and processes 72
5.1. Synthesis of high-performance separator 72
5.2. Characterization 72
5.2.1. Morphological and structural characterization. 72
5.2.2. Pore size and pore distribution 75
5.2.3. Mechanical properties 77
5.2.4. Electrolyte uptake, porosity, and wettability 79
5.2.5. Thermal stability 82
5.2.6. Electrochemical performance 84
5.2.7. Battery performance 86
5.2.8. Inhibition of lithium dendrite formation and growth 92
5.3. Concluding remarks 95
Chapter 6. Advanced sensing technology accurately predicting lithium-ion battery internal temperature 98
6.1. Experimental objects and devices 98
6.2. Experimental setup 99
6.3. SOC and SOH influence test on EIS 101
6.3.1. Influence of SOC on EIS 101
6.3.2. Influence of SOH on EIS 108
6.4. Influence of temperature on EIS 116
6.4.1. Model establishment 118
6.4.2. Validation of the model 119
6.5. Lithium-ion battery internal temperature online estimation strategy 121
6.6. Concluding remarks 123
Chapter 7. Summary and future work 125
7.1. Summary 125
7.2. Future work 127
References 129
Publications 155
요약 157
Table 1.1. Different principles of self-forming pores with different porous structures 30
Table 1.2. Main post-treatment methods for preparing porous materials 32
Table 3.1. Experimental parameters of electrospinning 53
Table 5.1. Ionic conductivities of the separators 86
Table 5.2. Schematic diagram of the relationship between the structure and performance of different separators 90
Table 6.1. Comparison of the temperature prediction results of model (a) 120
Table 6.2. Comparison of the temperature prediction results of model (b) 121
Figure 1.1. Schematic diagram of the lithium-ion battery structure 19
Figure 1.2. Diagram of the main properties required for the separators and the applications for LIBs 21
Figure 1.3. Battery sensing technology 22
Figure 1.4. Electrospinning device diagram 25
Figure 1.5. SEM image: (a) unbonded nanofibers; (b) bonded nanofibers; (c) Glue the intersections of two intersecting fibers 27
Figure 1.6. (a) SEM image of porous PLLA fibers. (b-d) SEM images of porous nanofibers composed of PCL, PAN, and PVDF, respectively 29
Figure 1.7. Experimental settings: (a) battery drilling program, (b) insulated batteries in the hot room, (c) uninsulated batteries with heat... 37
Figure 2.1. The device diagram of the electrostatic spinning process 45
Figure 2.2. Electrochemical impedance spectrum of lithium-ion battery 49
Figure 3.1. Separator fabrication and post-treatment process 53
Figure 4.1. SEM image of nanofibers: (a. b) NPT separator, (c. d) HD separator 63
Figure 4.2. Tensile strength of NPT and HD separator 64
Figure 4.3. Porosity and electrolyte uptake of the separators 65
Figure 4.4. SEM image of nanofibers: (a. b) NPT separator, (c. d) HT separator 67
Figure 4.5. (a) Microstructure of the NPT separator fracture site, (b) Microstructure of HT separator fracture site, (c) Test device, (d) Tensile... 69
Figure 4.6. Porosity and electrolyte uptake of the separators 70
Figure 5.1. SEM image of nanofibers: (a. b) NPT separator, (c. d) HT-HD separator 74
Figure 5.2. TEM image of nanofibers: (a) NPT separator; (b) HT separator; (c) HD separator; (d) HT-HD separator 75
Figure 5.3. (a) Average pore size, (b) Bet surface area, (c) Pore distribution, (d) Adsorption and desorption curves of HT-HD separator 77
Figure 5.4. Tensile strength of separators 79
Figure 5.5. (a) Porosity and electrolyte uptake of the separators; (b) FTIR spectra of HT-HD separator; (c) Electrolyte wettability behavior 82
Figure 5.6. (a) Percentage of weight/mass loss; (b) Exothermic behavior during the heat flow; (c) Thermal shrinkage of the separators before and... 84
Figure 5.7. (a) LSV of the separators; (b) Nyquist plot of the separators 86
Figure 5.8. Discharge capacity and voltage profiles of the separators at a current rate of (a) 0.2C; (b) 1C; (c) 5C; (d) Comparison of the discharge... 91
Figure 5.9. Different separator EDS corresponding to (a, d) Celgard; (b, e) No post-treatment; (c, f) Heat treatment combined hydrolysis; Anode... 95
Figure 6.1. Battery temperature test system 98
Figure 6.2. EIS test procedures at different SoC and temperatures 100
Figure 6.3. EIS test procedures at different SOH and temperatures 101
Figure 6.4. EIS of different SOC batteries at temperatures: a. 0 °C, b. 20 °C, c. 40 °C, d. 60 °C 103
Figure 6.5. Real part of different battery SOCs at temperatures: a. 0 °C, b. 20 °C, c. 40 °C, d. 60 °C 104
Figure 6.6. Imaginary part of different batteries SOC at temperatures: a. 0 °C, b. 20 °C, c. 40 °C, d. 60 °C 106
Figure 6.7. A amplitude of different batteries SOC at temperatures: a. 0°C, b. 20°C, c. 40°C, d. 60°C 107
Figure 6.8. Phase shift of different batteries SOC at temperatures: a. 0°C, b. 20°C, c. 40°C, d. 60° 108
Figure 6.9. EIS of different batteries (100%SOC) SOH at temperatures: a. 0 °C, b. 20 °C, c. 40 °C, d. 60 °C 110
Figure 6.10. The real part of different batteries SOH at temperatures: a. 0 °C, b. 20 °C, c. 40 °C, d. 60 °C 112
Figure 6.11. Imaginary part of different batteries SOH at temperatures: a. 0°C, b. 20°C, c. 40°C, d. 60°C 113
Figure 6.12. Amplitude of different batteries SOH at temperatures: a. 0°C, b. 20°C, c. 40°C, d. 60°C 114
Figure 6.13. The phase shift of different batteries SOH at a. 0°C, b. 20°C, c. 40°C, d. 60°C 115
Figure 6.14. 60% SOC battery at different temperatures: a. Nyquist plot, b. Rb, c. Relationship between imaginary part and frequency, d Fitting curves...[이미지참조] 118
Figure 6.15. Implementation strategy of battery internal temperature real-time estimation system schematic diagram 123