Morphology and Surface Reactivity Relationship in the Li_1+xMn_2-xO₄ Spinel with x = 0.05 and 0.10: A Combined...

This article focuses on the surface reactivity of two spinel samples with different stoichiometries and crystal morphologies, namely Li_1+xMn_2-xO₄ with x = 0.05 and 0.10. LiMn₂O₄ compounds are good candidates as positive electrode of high-power lithium-ion batteries for portable devices. The samples were investigated using both experimental and theoretical approaches. On the experimental point of view, they were characterized in depth from X-ray diffraction, scanning electron microscopy, and X-ray photoelectron spectroscopy (XPS) analyses. Then, the reactivity was investigated through the adsorption of (SO₂) gaseous probes, in controlled conditions, followed by XPS characterization. First-principle calculations were conducted simultaneously to investigate the electronic properties and the reactivity of relevant surfaces of an ideal LiMn₂O₄ material. The results allow us to conclude that the reactivity of the samples is dominated by an acido-basic reactivity and the formation of sulfite species. Nonetheless, on the x = 0.05 sample, both sulfite and sulfate species are obtained, the later, in lesser extent, corresponding to a redox reactivity. Combining experimental and theoretical results, this redox reactivity could be associated with the presence of a larger quantity of Mn⁴⁺ cations on the last surface layers of the material linked to a specific surface orientation.