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Study on Chemical Charge Transfer to Facilitate Highly Reversible Rechargeable Batteries

  • Jinkwan Choi (최진관, 대학원 신소재공학과 신소재공학전공)

초록/요약

Lithium-ion batteries are often called “rocking chair batteries”, originating from their high reversibility of the Li+ transfer between the cathode and the anode. However, some inherent irreversibility exists in LIBs. At the initial charging of the battery, irreversible lithium loss occurs due to the formation of SEI. For the compensation, several prelithiation strategies have been investigated so far, especially for the Si-based anode, which consumes more lithium than conventional graphite anode. The irreversible Li loss increases with the prolonged cycles by the evolving of SEI, and the capacity of the cell severely fades. Finally, the battery cannot conduct its original purpose due to its faded performance, but it can be revitalized by the recycling process. Chapter 1 presents an innovative strategy to chemically prelithiate the graphite-SiOx blended anode for high-energy lithium-ion batteries without structural destruction of graphite by controlling the solvation power of prelithiation solution. A reductive prelithiation solution composed of Li-arene and the solvent was designed by precise screening based on the solvation power of the solvent to protect the graphite from the irreversible co-intercalation of lithium and the solvent. Combined spectroscopy and density functional theory calculations reveal that in weakly solvating solutions, where the Li+-anion interaction is enhanced, free solvated-ion formation is inhibited during Li+ desolvation, thereby mitigating solvated-ion intercalation into graphite and allowing stable prelithiation of the blend. Given the ideal ICE of the prelithiated blend anode, a full cell exhibits an energy density of 506 Wh kg-1 (98.6% of the ideal value), with a capacity retention after 250 cycles of 87.3%. Chapter 2 introduces an advanced regeneration method for the cathode of lithium-ion batteries, in which coupling between lithium and recyclable electron donors (REDs). The redox potentials of REDs, strategically positioned between cathode operation and over-lithiation potentials, facilitate topotactic lithiation of spent cathodes without inducing detrimental side reactions under ambient conditions. The high chemical stability of REDs enables a closed-loop cathode recycling procedure, minimizing chemical waste. This work introduces an unprecedented chemical regeneration mechanism for spent cathodes, paving the way for the development of scalable and environmentally sustainable LIB recycling technologies. In conclusion, this thesis proposes how to relieve the irreversibility that occurs inside the LIBs from the beginning to the end of their life cycle so that we can utilize the batteries with their maximum energy density and revitalize them in a facile method. Assisted by thermodynamically driven spontaneous redox active behavior of organic redox molecules, Li+ was successfully transferred into the active material so that the reversible characteristics of the battery can be fully utilized.

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목차

ABSTRACT i
국문 초록 iii
PREFACE vi
TABLE OF CONTENTS viii
LIST OF TABLES x
LIST OF FIGURES xiii
CHAPTER 1. Weakly solvating solution Enables Chemical Prelithiation of Graphite−SiOx Anodes for High-Energy Li-Ion Batteries 1
1.1 Introduction 1
1.2 Experimental 4
1.3. Results and Discussion 8
1.3.1 Electrochemical Performances of Graphite, Si, SiOx, and Their Blends 8
1.3.2 Stable chemical prelithiation of graphite by mitigating solvated Li+ intercalation 16
1.3.3 Effect of solvation structure on Li+ ion intercalation into graphite 26
1.3.4 Prelithiation of Gr/Si Blend Systems 33
1.4. Conclusion 47
CHAPTER 2. Thermodynamically controlled chemical regeneration of spent battery cathodes using recyclable electron donors under ambient conditions 48
2.1. Introduction 48
2.2. Experimental 51
2.3. Results and Discussion 59
2.3.1. Thermodynamics of spontaneous charge transfer from DMPZ to Li-deficient NMC cathode 59
3.3.2. Electrochemical performance of NMC622 cathodes regenerated under practical conditions 73
2.3.3. Universality of our regeneration strategy 88
2.3.4. Circularity in RED-based regeneration process with minimal waste production 96
2.3.5. Regenerating NMC811 from a commercial pouch cell after extended cycling 108
2.4. Conclusion 141
CHAPTER 3. CONCLUDING REMARK 142
BIBLIOGRAPHY 144
CURRICULUM VITAE 153
ACKNOWLEDGEMENTS 154

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