SnO is an attractive negative electrode for Li-ion battery owing to its high specific charge compared to commercial graphite. However, the various intermediate conversion and alloy reactions taking place during lithiation/delithiation, as well as the electrolyte stability, have not been fully elucidated, and many ambiguities remain. An amorphous SnO thin film was investigated for use as a model electrode by a combination of postmortem X-ray photoelectron spectroscopy supported by density functional theory calculations and scanning electron microscopy to shed light on these different processes. The early stages of lithiation reveal the presence of multiple overlapping reactions leading to the formation of LiSnO and Sn phases between 2 and 0.8 V vs Li/Li. Between 0.45 V and 5 mV vs Li/Li LiSnO, LiO and Li Sn phases are formed. Electrolyte reduction occurs simultaneously in two steps, at 1.4 and 1 V vs Li/Li, corresponding to the decomposition of the LiPF salt and ethylene carbonate/dimethyl carbonate solvents, respectively. Most of the reactions during delithiation are reversible up to 1.5 V vs Li/Li, with the reappearance of Sn accompanied by the decomposition of LiO. Above 1.5 V vs Li/Li, Sn is partially reoxidized to SnO . This process tends to limit the conversion reactions in favor of the alloy reaction, as also confirmed by the long-term cycling samples.
The coupling mechanism of magnetic molecules to ferromagnetic surfaces is of scientific interest to design and tune molecular spintronic interfaces utilizing their molecular and surface architecture. Indirect magnetic coupling has been proposed earlier on the basis of density functional theory +U (DFT+U) calculations, for the magnetic coupling of manganese(II) porphyrin (MnP) molecules to thin Co films. Here we provide an experimental X-ray magnetic circular dichroism (XMCD) spectroscopy and scanning tunneling microscopy (STM) study of manganese(III) tetraphenylporphyrin chloride (MnTPPCl) on rough (exhibiting a high density of monatomic steps) and smooth (exhibiting a low density of monatomic steps) thin Co films grown on a Cu(001) single crystal toward the assessment of the magnetic coupling mechanism. After deposition onto the surface, MnTPPCl molecules were found to couple ferromagnetically to both rough and smooth Co substrates. For high molecular coverage, we observed higher XMCD signals at the Mn L-edges on the smooth Co substrate than on the rough Co substrate, as expected for the proposed indirect magnetic coupling mechanism on the basis of its predominance on the flat surface areas. In particular, DFT+U calculations predict a weak ferromagnetic molecule-substrate coupling only if the chloride ion of the MnTPPCl molecule orients away (Co-Mn-Cl) from the Co surface.
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