Influence of process conditions on direct and aqueous recycling of high nickel rich cathodes

With the increasing popularity of lithium ion batteries comes a corresponding increase in the number of aging batteries that will require recycling in the future. Direct recycling has the advantage of remaining the cathode material structure over other recycling methods (e.g. pyrometallurgy and hydrometallurgy) [1]. However, the technology readiness level (TRL) of direct recycling is still relatively low. One step in the direct recycling is the detachment of the electrode coating from the current collector, which often takes place in a water-based medium [2]. However, some cathode materials are highly sensitive to water, and the aluminum current collector may undergo side reactions at unsuitable pH values [3, 4]. Therefore, it is important to understand the potential side reactions that may occur during direct recycling in a water-based medium. In this study three different systems are analyzed: NMC811 + H₂O (only Li leaching), NMC811 + H₂O + Alu (Li leaching and Al corrosion), and NMC811 + H₂O + Alu + H₃PO₄
(increased Li leaching and no Al corrosion). The NMC811 of all three systems was further characterized by scanning electron microscopy (SEM), thermogravimetry (TG) and electrochemical cycling. Overall, the study demonstrated the importance and influence of process conditions during direct, aqueous recycling of NMC811 cathodes. The recycling of pure NMC811 in water resulted in poor electrochemical performance. The addition of aluminum foil in a corrosive environment improved capacity retention but resulted in lower discharge capacities due to higher amount of aluminum surface species on the NMC811. The process, which uses H₃PO₄ to prevent the corrosion of the aluminum current collector, a compromise between high discharge capacities and moderate capacity retention is achieved.

References:

[1] Boukhalfa S. et al., Market Report 2022, PRESCOUTER

[2] Horn D. et al, Conference on Future Automotive Technology, 2018.

[3] Kuenzel M. et al., ChemSusChem, 2018, 11, 562 –573

[4] Ahmad Z., IntechOpen, 2013, 978-953-51-0861-0