Efficient Separation of the Active Material Layer from Aluminum Foil of Spent Lithium Iron Phosphate Cathodes via Water Immersion

Establishing a low-cost, low-environmental-impact, and highly efficient method to separate lithium iron phosphate (LiFePO4, LFP) cathode active materials from the aluminum (Al) foil of spent LFP cathodes while preserving the crystal structure remains a challenge for direct regeneration of spent LFP cathodes. In this study, we proposed a separation method for the active material layer from Al foil by inducing interfacial hydrogen (H2) gas evolution during immersing spent LFP cathodes in ultrapure water. Regardless of the number of charge-discharge cycles or the solid-to-liquid ratio, complete separation was achieved within approximately 3 minutes even under mild stirring conditions, while the separation efficiency evaluated after 10 minutes exceeded 97%. Under optimized conditions, separation occurred within several tens of seconds. Analysis of the immersion solution suggested that lithium hexafluorophosphate (LiPF6), the electrolyte remaining in the spent cathode, partially hydrolyzed, generating acidic and fluorine-containing species. X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) indicated that the double-layer passivation film formed on the Al foil of the spent cathode, consisting of Al2O3 and AlF3, was locally thinned and removed by the fluorine species, exposing metallic Al. Micro-galvanic couples between the exposed metallic Al and carbon black (CB) in the active material layer are considered to trigger interfacial H2 gas evolution, thereby inducing separation at the interface. The recovered active material layer was characterized by inductively coupled plasma optical emission spectroscopy (ICP-OES) and X-ray diffraction (XRD), which confirmed that the lithium content and crystal structure were largely retained. This method shows promise as a rapid, highly efficient separation approach for the direct regeneration of spent LFP cathodes.