Recovery of metals and regeneration of cathode and anode from spent lithium-ion batteries using a deep eutectic solvent based on choline chloride and levulinic acid

다국어 초록 (Multilingual Abstract)

The rapid increase in electric vehicle adoption has led to a surge in end-of-life lithium-ion batteries, further highlighting the need for recycling pathways that reduce reliance on high- temperature processing and strong acid leaching. Here, we used a choline chloride-levulinic acid (ChCl-LA) deep-eutectic solvent (DES) system to leach metals from NCM black mass, followed by impurity removal, preparation of precursors for cathode regeneration, and coin cell testing. Under optimized ChCl–LA conditions (1:5 of molar ratio, 15 g/L of solid-to- liquid ratio, 180 °C of leaching temperature, and 1 h of leaching time), leaching efficiencies reached 95.7% for Co, 80.4% for Li, 99.6% for Mn, and 94.7% for Ni. After Cu was selectively removed using Acorga M5640, the leachate composition of Ni:Co:Mn was adjusted to 8:1:1. Then, via ammonia-assisted hydroxide co-precipitation (pH ≈ 11), lithiation and calcination, regenerated NCM811 was synthesized. The regenerated cathode in a coin cell exhibited an initial discharge capacity of 137.11 mAh/g and an initial coulombic efficiency of 75.2% at 0.5 C. It demonstrated stable cycling performance with a capacity retention of 90.6% after 30 cycles at 0.5 C. After rate testing up to 5 C, it recovered 95.2% of its capacity when returned to 0.2C. The regenerated graphite (RG) was manufactured by washing and heat treatment of spent graphite from anode, with additional activated graphite (AG) produced via steam activation. Both were compared and evaluated against natural graphite (NG). After 30 cycles at 2 C, the initial discharge capacities were 360.13 mAh/g (NG), 295.25 mAh/g (RG), and 304.64 mAh/g (AG). The discharge capacities of NG, RG, and AG after 30 cycles were 48.26, 124.61, and 124.24 mAh/g, respectively. The capacity retention rates from the 2nd to the 30th cycle were 14.7% (NG), 44.7% (RG), and 44.6% (AG), respectively. These results demonstrate an integrated approach including ChCl-LA DES leaching of black mass and regeneration of NCM cathodes and graphite anodes.

목차 (Table of Contents)

• TABLE OF CONTENTS i
• LIST OF FIGURES iv
• LIST OF TABLES vi
• Abstract vii
• 1. Introduction 1
• 1.1. Background of the research 1
• 2. Theoretical background 2
• 2.1. Components and operating principles of lithium-ion batteries 2
• 2.2. Types and characteristics of cathode materials 4
• 2.3. Recycling technologies for spent lithium-ion batteries 6
• 2.3.1. Pyrometallurgy 6
• 2.3.2. Hydrometallurgy 7
• 2.3.3. Direct recycling 8
• 2.4. Deep eutectic solvents (DES) and ChCl/LA system 10
• 2.4.1. Composition and characteristics of DES 10
• 2.4.2. DES-based lithium-ion battery recycling 11
• 2.5. Leaching and solvent extraction 14
• 2.5.1. Leaching 14
• 2.5.2. Solvent extraction 16
• 2.6. Regeneration of NCM cathode materials 19
• 2.6.1. Co-precipitation 21
• 2.6.2. Calcination 22
• 2.6.3. Pre-treatment and ball-milling 23
• 2.7. Regeneration of anode materials 23
• 2.8. Objectives and scope of this study 24
• 3. Materials and methods 28
• 3.1. Materials 28
• 3.2. Methods 28
• 3.2.1. Preparation of ChCl/LA-based DES 28
• 3.2.2. Leaching of black mass 29
• 3.2.3. Solvent extraction for Cu removal 30
• 3.2.4. Manufacturing of regenerated cathode material 30
• 3.2.4.1. Co-precipitation of the precursor 31
• 3.2.4.2. Milling and calcination of the precursor 32
• 3.2.5. Manufacturing of regenerated anode materials 33
• 3.2.5.1. Regeneration of spent graphite (RG) 33
• 3.2.5.2. Steam activation of regenerated graphite (AG) 33
• 3.3. Regenerated cathode material characterization 34
• 3.4. Regenerated anode material characterization 34
• 3.5. Electrode fabrication, coin-cell assembly, and electrochemical performance analysis 34
• 4. Results and discussion 36
• 4.1. Composition of black mass 36
• 4.2. Preparation of ChCl/LA solvent 37
• 4.2.1. pH, viscosity measurements 37
• 4.2.2. FT-IR analysis 37
• 4.3. Leaching experiments 39
• 4.3.1. Effect of molar ratio on metal leaching efficiency 39
• 4.3.2. Effect of solid-liquid ratio on metal leaching efficiency 42
• 4.3.3. Effect of leaching temperature on metal leaching efficiency 43
• 4.3.4. Effect of leaching time on metal leaching efficiency 44
• 4.4. Copper removal using Acorga M5640 45
• 4.5. Regeneration of cathode materials 46
• 4.6. Regeneration of anode materials 51
• 4.7. Electrochemical performance 56
• 4.7.1. Regenerated cathode materials 56
• 4.7.2. Regenerated anode materials 60
• 5. Conclusions 66
• 6. References 68
• Abstract in Korean 73