Materials Recovery and Upgrade from Spent Lithium-ion Batteries

Ma, Xiaotu

Etd

Materials Recovery and Upgrade from Spent Lithium-ion Batteries

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Due to the rapid development of Lithium-ion batteries (LIBs), recycling spent LIBs plays a significant role in alleviating the shortage of raw materials, human health, and environmental problems. Although academic innovations and industrial demonstrations of pyrometallurgy, hydrometallurgy, and direct recycling processes are constantly emerging and attempting to make an impact, none of the current recycling technologies is perfect, and challenges do exist. Especially with the rapidly increasing market demand and subsequent retirement of cobalt-lean cathodes, traditional recycling processes may lose their advantages and profits. To overcome these barriers, the recycling process needs to enrich its profit structure and develop new sustainable technology. In the past several years, our team at WPI has developed a closed-loop recycling process, and the recovered LiNi1/3Mn1/3Co1/3O2 (NMC 111) has similar or better electrochemical performance than the commercial control NMC 111 powder. To further realize the profitability and sustainable development of recycling, this dissertation optimized the traditional recycling process and designed a direct upcycling process to make recycling spent LIBs more economical and sustainable. First, due to the rapid development of Lithium-ion batteries, recycling spent Lithium-ion batteries plays a significant role in alleviating the shortage of raw materials and environmental problems. However, recycled materials are deemed inferior to commercial materials, preventing the industry from adopting recycled materials in new batteries. Here, we demonstrate that the recycled LiNi1/3Mn1/3Co1/3O2 has a superior rate and cycle performance, verified by various industry-level tests. Specifically, 1 Ah cells with the recycled LiNi1/3Mn1/3Co1/3O2 have the best cycle life result reported for recycled materials and enable 4,200 cycles and 11,600 cycles at 80% and 70% capacity retention, which is 33% and 53% better than the state-of-the-art, commercial LiNi1/3Mn1/3Co1/3O2. Meanwhile, its rate performance is 88.6% better than commercial powders at 5C. From experimental and modeling results, the unique microstructure of recycled materials enables superior electrochemical performance. The recycled material outperforms commercially available equivalent, providing a green and sustainable solution for spent lithium-ion batteries. Second, due to the low added value, graphite anode materials in spent LIBs are discarded. Currently, the market price of the graphite anode is around $8−13/kg, which could account for 10−15% of the material cost in typical LIBs. Meanwhile, the graphite content of spent LIBs ranges from 12 to 21 wt. %. As the number of spent LIBs increases, the amount of waste graphite becomes quite large. Therefore, we optimized our closed-loop recycling process with a scalable, high-quality graphite anode recycling process. After the leaching process, graphite was separated by filtration as a residue with impurities. Then, residual cathode materials, metal impurities, binder materials, and aluminum oxide were removed after re-leaching and fusion steps. Finally, high-quality graphite powder was obtained, and the recycled graphite exhibits a comparable discharge capacity of 377.3 mAh/g at 0.1 C. Then, LiNixMnyCo1-x-yO2 (NMC) is considered the most appealing cathode material due to its high energy density and low cost. However, the stability and safety concerns caused by the degradation of polycrystalline cathode materials during cycling have restricted their practical applications. To overcome this shortcoming, converting polycrystalline cathode to high-performance single-crystal cathode materials becomes an appealing solution. Here, a universal etching approach is firstly developed to synthesize single-crystal cathode materials. As a result, the rate performance of obtained single-crystal NMC111 is 10–15% more than that of polycrystalline NMC111, whereas the capacity retention of single-crystal NMC111 is enhanced by ~12% after 300 cycles at 0.5C. Furthermore, the obtained single-crystal NMC622 exhibits a pronounced improvement in rate performance, especially at high rates (~28.6% better at 5C and ~129% better at 10C) and has a comparable cycle performance compared to polycrystalline NMC622. Altogether, the findings propose an alternative approach to generate single-crystal particles with high energy density and cycle stability for the next-generation lithium-ion batteries. And since this method is a simplified leaching process, it is possible to be utilized in the recycling process to convert polycrystalline to high-performance single-crystal materials. Finally, most recycling processes focus on recovering cathode materials with the same composition, structure, and electrochemical properties as the original cathode materials in spent LIBs. However, throughout the rapid evolution of cathode materials, the demand for cathode materials will trend towards high energy density and long cycle life cathode materials. To increase competitiveness, make recycling profitable and realize the real sustainable process recovered cathode materials must keep abreast of the market demand. Although the hydrometallurgical process is the only process that can change the composition of recovered cathode materials among the three traditional recycling processes, the hydrometallurgical process always involves toxic solvents and concentrated acids for recovery, which possibly lead to health problems and safety hazards associated with the dangerous materials handled during the manufacturing process. Thus, we designed a direct upcycling process to covert spent cathode materials to more current cathode formulations relevant to the marketplace. We obtained single-crystal NMC622 cathode powder from commercial NMC111 cathode powder via a simple molten salt method. The obtained single-crystal NMC622 shows similar performance at a low rate and over 10% better performance at 2C, 5C, and 10C. We are working on verification whether this process can apply to upcycle the spent NMC111.

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