Influence of Process Conditions During Aqueous and Direct Recycling of NMC811 Cathodes.

Abstract

This study investigated the impact of various process conditions on the aqueous, direct recycling of LiNi_0.8Mn_0.1Co_0.1O₂ (NMC811) cathodes. Three model systems were used. The first system assumes that the current collector delamination is performed in a dry environment without the use of water as a process medium. Consequently, the NMC811 is only exposed to water during classification, where no aluminum foil is present. The second model system assumes that the current collector delamination occurs in water. Therefore, the NMC811 is exposed to water in the presence of aluminum foil. Due to the pH increase caused by the Li⁺/H⁺ exchange reaction, the pH value surpasses the stability window of the aluminum-oxide passivation layer (pH 4.5-8.5), resulting in the deposition of aluminum-containing species on the NMC811 surface. The third model system is identical to the second, with the exception that H₃PO₄ is added. This causes the pH to decrease and prevents corrosion of the aluminum foil. The findings reveal that process conditions significantly affect the surface chemistry on NMC811, influencing electrochemical performance. Notably, aluminum-containing species increase polarization. Heat treatment simulating regeneration led to cation mixing as surface species diffused into the NMC811 bulk structure, highlighting the need to control recycling process conditions.