Removal of residual contaminants by minute-level washing facilitates the direct regeneration of spent cathodes from retired EV Li-ion batteries

Abstract

The direct regeneration of spent cathodes stands out as an environmentally and economically benign strategy within the battery ecosystem, eclipsing the cumbersome metallurgical approaches. Before addressing the lithium loss and structural degradation, it is crucial to focus on the residual contaminants within the spent cathode collected from retired Li-ion batteries after industrial exfoliation processes. Here, comprehensive characterizations and calculations show that in contrast to metal scraps, the electrolyte decomposition after battery operation and heating exfoliation uniformly coat the particle surfaces of cathodes, severely impeding the reuse and rejuvenation of LiNi_xCo_yMn_zO₂ (NCM) cathodes with limited degradation by obstructing lithium diffusion. Considering the high costs and environmental risks of organic systems, we further propose a minute-level water-based pretreatment to purify the spent cathode and selectively eliminate these stubborn impurities that can deteriorate the interfacial chemical state, even after prolonged high-temperature heat treatment. Combined with a solid-state regeneration process, a purified 250k-miles-serviced (8 year) cathode could be rejuvenated to match the pristine one's capacity and cycling retention, displaying a 1.9-fold increase in average lithium diffusivity for charging and 43% enhanced capacity retention after 200 cycles compared with the unpurified one. Our study underscores the critical role of previously overlooked chemical residuals in facilitating the practical direct regeneration of retired lithium-ion batteries.