Michel Rosso

The realization of metal‐organic framework (MOF) layers onto solid surfaces is a prerequisite for their integration into devices. This work reports the direct growth of Fe³⁺/benzene di‐carboxylate MOFs onto functionalized silicon surfaces, compatible with a wide range of MOF synthesis conditions. The co‐nucleation and growth of different crystalline phases are evidenced, whose coverage depends on the surface chemistry and/or the solution composition. Three structural phases – the cubic MIL‐101(Fe), a hexagonal phase with a structure close to MOF‐235 and a MIL‐53(Fe) with a monoclinic symmetry ‐ are identified through characteristic crystal shapes and their structural parameters inferred from X‐Ray Diffraction. In addition to the oriented growth of 3D crystallites, the formation of two‐dimensional MIL‐101 nano‐crystallites or thin layers/islands exhibiting extended monocrystalline domains with (111) texture is also demonstrated through high‐resolution atomic force microscopy. Post‐synthesis treatments reveal a weak adhesion of the hexagonal phase, indicating a different surface anchoring.

Correction for ‘In situ interferometry study of ionic mass transfer phenomenon during the electrodeposition and dissolution of Li metal in solvate ionic liquids’ by Akinori Miki et al., J. Mater. Chem. A, 2021, DOI: 10.1039/d1ta02666f.

The lithiation mechanism of methylated amorphous silicon, a‐Si_1−x(CH₃)_x:H, with various methyl contents (x = 0 ‐ 0.12) is investigated using operando attenuated total reflection Fourier transform infrared spectroscopy. As in hydrogenated amorphous silicon, a‐Si:H, the first lithiation proceeds via a two‐phase mechanism. The concentration of the invading Li‐rich phase nonmonotonously depends on the methyl content of the active material. This behavior is tentatively explained by two distinct effects: a softening of the material due to a methyl‐induced lowering of its reticulation degree and its cohesion, and the presence of nanovoids at high enough methyl content.

Multiple‐internal‐reflection infrared spectroscopy allows for the study of thin‐film amorphous silicon electrodes in situ and in operando, in conditions typical of those used in Li‐ion batteries. It brings an enhanced sensitivity, and the attenuated‐total‐reflection geometry allows for the extraction of quantitative information. When electrodes are cycled in representative electrolytes, the simultaneously recorded infrared spectra give an insight into the solid/electrolyte interphase (SEI) composition. They also unravel the dynamic behavior of this SEI layer by quantitatively assessing its thickness, which increases during silicon lithiation and partially decreases during delithiation. Li‐ion solvation effects in the vicinity of the electrode indicate that lithium incorporation in the solid phase is the rate‐determining step of the electrochemical processes during lithiation. The lithiation of the active material also results in the irreversible consumption of a large quantity of hydrogen in the pristine material. Finally, the evolution of the electronic absorption of the electrode material suggests that lithium diffusion is much easier after the first lithiation than in the pristine material. Therefore, in situ Fourier‐transform infrared spectroscopy performed in a well‐suited configuration efficiently extracts original and quantitative pieces of information on the surface and bulk phenomena affecting Li‐ion electrodes during their operation in realistic conditions.

Si thin films obtained by plasma enhanced chemical vapor deposition (PECVD) were used to investigate chemical and morphological modifications induced by lithiation potential and cycling. These modifications were thoughtfully analyzed by time-of-flight secondary ion mass spectrometry (ToF-SIMS) depth profiling, which allows to distinguish the surface and bulk processes related to the formation of the solid electrolyte interphase (SEI) layer, and Li-Si alloying, respectively. The main results are a volume expansion/shrinkage and a dynamic behavior of the SEI layer during the single lithiation/delithiation process and multicycling. Trapping of lithium and other ions corresponding to products of electrolyte decomposition are the major reasons of electrode modifications. It is shown that the SEI layer contributes to 60% of the total volume variation of Si electrodes (100 nm). The apparent diffusion coefficient of lithium (DLi) calculated from the Fick's second law directly from Li-ion ToF-SIMS profiles is of the order of ∼5.9 × 10(-15) cm(2).s(-1). This quite low value can be explained by Li trapping in the bulk of electrode material, at the interfaces, continuous growth of the SEI layer and increase of SiO2 quantity. These modifications can result in limitation the ionic transport of Li.