Regeneration of Spent Graphite from Lithium-Ion Batteries by Malic-Acid Leaching and Alkaline EDTA Chelation

The electrochemical reuse of spent graphite from the negative electrodes of lithium-ion batteries is influenced by regeneration-induced changes in near-surface chemical and defect states. These states govern solid electrolyte interphase (SEI) re-formation, particularly when bulk contaminants are suppressed. Acidic malic-acid leaching and ethylenediaminetetraacetic acid chelation under alkaline conditions (pH 8.7) were compared under similar operating parameters to isolate the role of the leaching environment. This was followed by heat treatment at 1200 °C to decouple chemical cleaning from structural restoration. Both methods reduced the total impurities from 217.85 ppm to ~1.8 ppm, approaching that of commercial graphite. Despite the comparable bulk purity, depth-resolved X-ray photoelectron spectroscopy after formation cycling revealed distinct outermost surface states relevant to SEI re-formation: acidic processing yielded a more oxygenated carbon signature and higher LiOH fraction at the outermost surface (~16%), whereas alkaline chelation produced a more graphitic, carbonate-dominated surface with lower LiOH (~7%). Electrochemical and impedance measurements were consistent with these differences, suggesting that after the bulk impurities were minimized, resistance development was largely governed by the leaching-conditioned near-surface state, which biased the SEI composition. The comparison under matched conditions linked the regeneration environment to SEI-relevant surface speciation and provided a mechanistic basis for selecting regeneration routes to reuse spent graphite as a negative-electrode active material.