Date

2022-12-28

Author

Tekmanlı, Fırat

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Since lithium-ion batteries are standard in electric vehicles and electrical devices and have the potential to be used widely in the future, it is essential to recycle end-of-life batteries. Waste lithium-ion batteries are harmful to the environment and human health and should be recycled also due to their critical metals. Lithium-ion batteries can be classified according to their cathode chemistry. In this thesis, the recycling of lithium-ion batteries with NMC-type (Nickel- Manganese-Cobalt) cathode chemistry was discussed. Two different approaches have been studied for the recycling of waste batteries. The first approach concerns the use of cathode active materials to make new electrodes by stripping them from the current collector foil and directly turning them into sludge. Three different methods have been studied for this approach. These are pyrolysis method, dissolution of PVDF method and dissolving of aluminum foil method. The pyrolysis method shows negative contribution on the performance of cathode active materials in terms of both capacity and cycle life. The dissolution of PVDF method shows promising electrochemical results but the residual PVDF leads to particle agglomeration which is not desired. In the dissolution of aluminum method, residual aluminum leads poor capacity retention. The other approach is to leach waste lithium ion cathodes with acid and then synthesize new cathode active material by direct co-precipitation method with the obtained leaching solution. In this approach, up to 99% Li, 97% Ni, 96% Co and 98% Mn by weight are recovered from the cathode mass and new cathode active materials were synthesized via co-precipitation method. The electrode prepared with this material shows 94.2% capacity retention after 50 cycle and discharge capacities at first and final were 151.58 mAh/g and 142.83 mAh/g,respectively, at 0.5C rate with the reference capacity of NMC-111 is 155 mAh/g. In both approaches, the aim is to create a closed-loop recycling process and to eliminate the extra steps as in conventional methods. Many pyrometallurgical and hydrometallurgical studies have been carried out worldwide for recycling processes. Still, it is not a closed-loop process yet, and hydrometallurgical studies with various acids and reducing agents need optimization. Lithium-ion batteries, intended to be recycled by hydrometallurgical methods, not by pyrometallurgical modes in terms of environmental pollution, are disassembled in this thesis. The emission of HF gas during the processes was investigated and its effect on the cathode properties was investigated. Acid leaching was carried out with various acids and reducing agents. Eventually, the closed-loop recycling and resynthesis processes successfully demonstrated the targeted performance.

Subject Keywords

Recycling, Li-ion battery, Leaching, Closed-loop recycling, Co-precipitation

URI

https://hdl.handle.net/11511/101866

Collections

Graduate School of Natural and Applied Sciences, Thesis