| Title |
Crystallographic Insights into Differences in Lithium Leaching Behavior between Reagent-grade and Recycled NCM Powder in Oxalic Acid Leaching |
| Authors |
김대원(Dae-Weon Kim) ; 김희선(Hee-Seon Kim) ; 김성원(Seong-Won Kim) ; 김재찬(Jae-Chan Kim) |
| DOI |
https://doi.org/10.3365/KJMM.2026.64.7.655 |
| ISSN |
1738-8228(ISSN), 2288-8241(eISSN) |
| Keywords |
NCM; Oxalic acid; Lithium leaching; Recycling; Crystallographic structure |
| Abstract |
This study comparatively investigated the differences in lithium leaching behavior between reagent-grade NCM and recycled NCM(R-NCM) powders using eco-friendly oxalic acid from crystallographic and kinetic perspectives. Both powders were characterized by ICP-OES, PSA, SEM, XRD, and GSAS-II Rietveld refinement, and leaching experiments were conducted in 0.5 M oxalic acid at 40, 60, and 80°C. Recycled R-NCM showed very high initial Li leaching efficiencies of 86-89% within 10 min at all temperatures, followed by a gradual decrease or stagnation with time. In contrast, reagent-grade NCM exhibited a clear time and temperature dependent leaching behavior, reaching nearly complete Li extraction of approximately 99.9% at 80°C after 80 min. XRD and Rietveld analysis revealed that reagent-grade NCM retained a highly ordered layered structure with a high I003/I104 ratio and a smaller cation mixing, whereas recycled R-NCM showed a reduced I003/I104 ratio, c-axis contraction, and changed Li slab height, indicating increased cation disorder and structural degradation. Kinetic analysis showed that Li leaching from reagent-grade NCM was most consistently described by the product-layer diffusion equation of the shrinking-core model, indicating product-layer-diffusion-dominant mixed control behavior. Based on origin-fixed uncentered R2, the fitting values were 0.9809, 0.9142, and 0.8627 at 40, 60, and 80°C, respectively, and the apparent activation energy derived from the Arrhenius plot was 39.6 kJ/mol. These results indicate that the lower final lithium recovery of recycled powder is closely related to layered-structure degradation, Li slab change, increased cation mixing, and hindered Li diffusion pathways. |