Surface Reactivity of Li₂MnO₃: First-Principles and Experimental Study

Abstract

This article deals with the surface reactivity of (001)-oriented LiMnO crystals investigated from a multitechnique approach combining material synthesis, X-ray photoemission spectroscopy (XPS), scanning electron microscopy, Auger electron spectroscopy, and first-principles calculations. LiMnO is considered as a model compound suitable to go further in the understanding of the role of tetravalent manganese atoms in the surface reactivity of layered lithium oxides. The knowledge of the surface properties of such materials is essential to understand the mechanisms involved in parasitic phenomena responsible for early aging or poor storage performances of lithium-ion batteries. The surface reactivity was probed through the adsorption of SO gas molecules on large LiMnO crystals to be able to focus the XPS beam on the top of the (001) surface. A chemical mapping and XPS characterization of the material before and after SO adsorption show in particular that the adsorption is homogeneous at the micro- and nanoscale and involves Mn reduction, whereas first-principles calculations on a slab model of the surface allow us to conclude that the most energetically favorable species formed is a sulfate with charge transfer implying reduction of Mn.

Understanding the Role of Alumina (Al2O3), Pentalithium Aluminate (Li5AlO4), and Pentasodium Aluminate (Na5AlO4) Coatings on the Li and Mn‐Rich NCM Cathode Material 0.33Li2MnO3·0.67Li(Ni0.4Co0.2Mn0.4)O2 for Enhanced Electrochemical Performance

“…We suggest that the feature at ≈529.9 eV in the O‐spectra of the Li‐aluminate and Na‐aluminate coated HE‐NCM materials (Figure 3a) may relate to a contribution from some spinel‐like structure. [ 51,52 ] Figure 3b shows the Mn 3s spectra of uncoated and Li‐aluminate and Na‐aluminate coated HE‐NCM materials. The splitting of Mn 3s peak is likely due to the coupling with the 3d valence band.…”

Surface reactivity of Li2MnO3: Structural and morphological impact

“…The acidbase adsorption mode is favored for large SF ratio and small particles as the accessible oxide anion, needed to form sulfate species, at the extreme surface is decreasing due to the overstoichiometry in Lithium ions. According with the particles shape evolution with the stacking fault contents, we must also consider the role of the manganese environment and the surface index on the adsorption mode 11 .…”

“…The binding energy values of the Mn 2p 1/2 (654.3 eV) and Mn 2p 3/2 (642.3 eV) main components as well as the splitting B.E. value of the Mn 3s core peak (4.5 eV-4.2 eV) are characteristic of tetravalent manganese atoms in an oxygenated environment 11,12 . As no shoulder has been observed at 641.4 eV 11 , the presence of Mn 3+ cations could be excluded.…”

“…The coating was shown first to form an interphase 9 , a substituted Al-layered oxide, at the interface between the coating Al 2 O 3 and the active material LiMO 2 , and then to decrease the surface reactivity toward the gaseous probes and changes the nature of the adsorbed species 9 . Following the same strategy, we recently focused on the role of manganese oxidation states on the surface reactivity through the investigation of Li 2 Mn 4+ O 3 and LiMn 3+,4+ 2 O 4 materials 11,12 . Depending on the nature of the manganese species present at the extreme surface of the material, Mn 3+ and/or Mn 4+ , acid-base and/or redox type reactivity is involved at the surface.…”

“…In a previous study, we studied the characteristic of the (001) surface of a Li 2 MnO 3 crystal containing 50% of stacking fault 11 . Thus, in this paper, we choose to get even deeper understanding of the surface reactivity of Li 2 MnO 3 by investigating the role of the morphology moving from crystals to powders showing a wide range of specific surface areas and stacking faults by controlling the annealing temperature.…”