Recycling of Spent Cathode Materials from Lithium-Ion Batteries Using Various Solvents under Supercritical Conditions
- 발행기관 서강대학교 일반대학원
- 지도교수 임종성
- 발행년도 2025
- 학위수여년월 2025. 8
- 학위명 박사
- 학과 및 전공 일반대학원 화공생명공학과
- 실제 URI http://www.dcollection.net/handler/sogang/000000081778
- UCI I804:11029-000000081778
- 본문언어 영어
- 저작권 서강대학교 논문은 저작권 보호를 받습니다.
초록 (요약문)
The unprecedented expansion of lithium-ion batteries (LIBs) for electric vehicles, consumer electronics, and grid-scale energy-storage systems has triggered an equally rapid accumulation of end-of-life cells. Spent LIBs are enriched with critical metals—lithium (Li), nickel (Ni), cobalt (Co), and manganese (Mn)—as well as polymeric binders such as poly (vinylidene fluoride) (PVDF). Conventional recycling—dominated by high-temperature pyrometallurgy or strong-acid hydrometallurgy—suffers from excessive energy demand, toxic off-gas evolution (e.g., HF from PVDF pyrolysis), large wastewater volumes, and complex downstream neutralization. Hence, environmentally benign and cost-effective alternatives are urgently required. This dissertation develops a supercritical CO₂ (scCO₂)–based, three-stage flowsheet that simultaneously upgrades the pre-treatment (binder extraction and electrode delamination) and post-treatment (metal recovery) steps of LIB recycling. In Stage 1, PVDF and water-based binders—carboxymethyl cellulose (CMC), poly(acrylic acid) (PAA), and poly(vinyl alcohol) (PVA)—are selectively dissolved in scCO₂ containing trace cosolvents (dimethyl sulfoxide (DMSO), dimethylformamide (DMF), N-methyl-2-pyrrolidinone(NMP), dimethylacetamide (DMAc) or H₂O). Under optimized conditions (353.15 K, 8– 10 MPa, 15–30 min), removal efficiencies reach 95–99 % for PVDF and 85–95 % for aqueous binders, enabling quantitative delamination of cathode coatings from aluminum current collectors. Fourier-transform infrared spectroscopy (FT-IR), Differential scanning calorimetry (DSC), Scanning electron microscopy (SEM), and X-ray diffraction (XRD) confirm that the recovered binders retain their chemical signatures. To assess their functional integrity, the extracted binders were reused to fabricate coin-type half-cells, and electrochemical performance tests showed negligible differences in initial discharge capacity and cycling stability compared to cells using pristine binders, demonstrating that the recovery process does not compromise binder quality. Stage 2 applies the delaminated NCM622 and NCA powders to an scCO₂ leaching protocol that introduces acetylacetone (AcAc) and a minor dose of H₂O₂. Operated at 313.15–333.15 K and 20–30 MPa, the process achieves 80–90 % dissolution of Ni, Co, and Mn and ~60 % recovery of Li, without recourse to high-temperature calcination or concentrated mineral acids. Kinetic analysis follows a diffusion-controlled shrinking-core model, while microscopy indicates outward-in metal removal with negligible secondary effluent. Overall, this study establishes a closed-loop scCO₂ platform that unifies high- efficiency binder extraction and valuable-metal recovery in a single, low- temperature, low-emission framework. By displacing energy-intensive pyro- or acid-based practices, the proposed strategy offers marked advantages in operational safety, waste minimization, and economic viability, providing a pathway toward sustainable LIB recycling.
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Contents ⅰ
List of Figure ⅵ
List of Table ⅹⅴ
Abstract (in Korean) ⅹⅴⅰ
Abstract ⅹⅰⅹ
Chapter 1 Introduction 1
1. 1. Background and significance 1
1. 2. Supercritical fluids 5
1. 3. PVDF and water-based binders 8
1. 4. Metals (Ni, Co, Mn, Li) in Lithium-Ion Batteries 14
1. 5. Conventional approaches and limitations 18
1. 6. Proposed scCO₂-based strategy and research objectives 21
1. 7. References 23
Chapter 2 Extraction of polyvinylidene fluoride binder materials 27
2. 1. Introduction 27
2. 2. Materials and methods 31
2. 2. 1. Materials 31
2. 2. 2. Solubility experiment 33
2. 2. 3. Binder extraction experiment 38
2. 2. 4. Evaluation of the cell performance 42
2. 3. Result and discussion 43
2. 3. 1. Solubility measurement 43
2. 3. 2. Binder extraction using SC-CO2 59
2. 3. 3. Evaluation of cell performance 73
2. 4. Conclusion 76
2. 5. References 78
Chapter 3 Extraction of water-based binder materials 82
3. 1. Introduction 82
3. 2. Materials and methods 86
3. 2. 1. Materials 86
3. 2. 2. Solubility experiment 88
3. 2. 3. Binder extraction experiment 90
3. 2. 4. Investigation of cell performance characteristics 92
3. 3. Result and discussion 93
3. 3. 1. Solubility analysis 93
3. 3. 2. Separation of Binders Using Supercritical CO2 105
3. 3. 3. Evaluation of cell performance 118
3. 4. Conclusion 123
3. 5. References 125
Chapter 4 Active‑Material Delamination from LIB Cathodes 130
4. 1. Introduction 130
4. 2. Materials and methods 133
4. 2. 1. Materials 133
4. 2. 2. Delamination of cathode active material 134
4. 3. Result and discussion 138
4. 3. 1. Effect of Pressure and Temperature on Delamination Efficiency 138
4. 3. 2. Batch vs. Continuous Extraction Performance 139
4. 3. 3. Influence of Co-Solvent Type (DMSO vs. DMF) 143
4. 3. 4. Delamination Kinetics at Optimal Conditions 145
4. 4. Conclusion 149
4. 5. References 150
Chapter 5 Extraction of Li, Ni, Co, and Mn from Active‑Material 153
5. 1. Introduction 153
5. 2. Materials and methods 155
5. 2. 1. Materials 155
5. 2. 2. Extraction of Metals from Cathode Active Materials 155
5. 3. Result and discussion 158
5. 3.1. Composition of Pristine NCM622 Cathode Material 158
5. 3.2. Effect of Process Parameters and Empirical Modeling 160
5. 3.3. Extraction Efficiency under Optimized Solvent Conditions 167
5. 3.4. kinetic analysis 171
5. 3.5. Morphological and Compositional Changes (SEM–EDS) 184
5. 3.6. Structural Transformations (XRD Analysis), Thermal Stability
Changes (DSC Analysis) 189
5. 3.7. Extension of the scCO₂ Process to an Al-Doped Cathode (NCA) 194
5. 4. Conclusion 196
5. 5. References 198
Chapter 6 Conclusion 201
List of Figure
Fig. 1. 1. A phase diagram of supercritical fluid 7
Fig. 1. 2. Structure of polyvinylidene fluoride 9
Fig. 1. 3. Structure of water based binder: (a)CMC; (b) PAA; (c)PVA
13
Fig. 1. 4. Schematic illustration of the working principle of a lithium-
ion battery (LIB) 17
Fig. 1. 5. Process flow diagram of lithium-ion battery (LIB)
recycling via hydrometallurgical treatment 20
Fig. 2. 1. A schematic diagram of the experimental apparatus for
solubility measurement 37
Fig. 2. 2. A schematic diagram of the experimental apparatus for
scCO2 extraction experiment: 41
Fig. 2. 3. P-T diagram of CO2 solubilities of the PVDF + CO2 system:
DMSO 48
Fig. 2. 4. P-T diagram of CO2 solubilities of the PVDF + CO2 system:
NMP 49
Fig. 2. 5. P-T diagram of CO2 solubilities of the PVDF + CO2 system:
DMAc 50
Fig. 2. 6. P-T diagram of CO2 solubilities of the PVDF + CO2 system:
DMF 51
Fig. 2. 7. Solubility of the PVDF + CO2 system (3D plot) by a two-
dimensional (2D) polynomial: DMSO 55
Fig. 2. 8. Solubility of the PVDF + CO2 system (3D plot) by a two-
dimensional (2D) polynomial: NMP 56
Fig. 2. 9. Solubility of the PVDF + CO2 system (3D plot) by a two-
dimensional (2D) polynomial: DMAc 57
Fig. 2. 10.Solubility of the PVDF + CO2 system (3D plot) by a two-
dimensional (2D) polynomial: DMF 58
Fig. 2. 11. Diagram of PVDF extraction yield of the cosolvent + SC-
CO2 system: temperature 61
Fig. 2. 12. Diagram of PVDF extraction yield of the cosolvent + SC-
CO2 system: pressure 63
Fig. 2. 12. Diagram of PVDF extraction yield of the cosolvent + SC-
CO2 system: pressure 65
viii
Fig. 2. 14. DSC curve of raw and recovered PVDF: (a) raw; (b)
DMSO; (c) NMP; (d) DMAc; (e) DMF 69
Fig. 2. 15. FT-IR spectra of raw and recovered PVDF: (a) raw; (b)
DMSO; (c) NMP; (d) DMAc; (e) DMF 71
Fig. 2. 16. SEM images of raw and recovered PVDF: (a) raw; (b)
DMSO; (c) NMP; (d) DMAc; (e) DMF 72
Fig. 2. 16. Capacity-voltage profiles of the initial charge-discharge
process 74
Fig. 2. 17. Cycling stabilities of the cells obtained using raw and
recovered PVDF binder 75
Fig. 3. 1. A schematic diagram of the experimental apparatus for
solubility measurement 89
Fig. 3. 2. A schematic diagram of the experimental apparatus for
scCO2 extraction experiment (batch) 91
Fig. 3. 3. P-T diagram of CO2 solubilities of the water-based binder
+ H2O + CO2 system: CMC 97
Fig. 3. 4. P-T diagram of CO2 solubilities of the water-based binder
+ H2O + CO2 system: PAA 98
