Crystallographic re-equilibration and chemical state evolution in spinel LiMn 2 O 4 modified by post-calcination Li–Fe incorporation

The crystallographic and chemical-state evolution of spinel LiMn2O4 after post-calcination Li–Fe modification was investigated by XRD/Rietveld refinement, XPS, SEM/EDS, and TEM. All modified samples retained the cubic Fd-3m spinel framework without detectable crystalline secondary phases. The nearly unchanged I (311)/I (400) ratio suggests that Fe is incorporated predominantly at 16d octahedral sites, with no clear evidence of substantial occupation of 8a lithium diffusion pathways. Rietveld refinement revealed a non-monotonic lattice response, showing slight expansion at low Li–Fe contents and contraction at the highest modification level. Surface-sensitive XPS analysis indicates that lattice contraction correlates with a higher surface Mn4+/Mn3+ ratio and more abundant defect-related oxygen-containing species, pointing to local charge-compensation effects and alteredmetal–oxygen bonding. SEM/EDS and TEM confirmed preserved morphology and relatively uniform elemental distribution. These results demonstrate coupled structural and electronic re-equilibration in Li–Fe-modified LiMn₂O₄.