Florent Robert

The good reactivity of lithium with nanostructured copper phosphide

In Li-ion battery technology, Li diffusion in the electrode is mainly limited by the quality of the interfaces. To take advantage of the large capacity gain offered by the transition metal phosphides (TMP) as negative electrode, a new self-supported TMP/Cu nanoarchitectured electrode concept is proposed. This specific design allows one to fine-tune control of both (TMP)/current collector and (TMP)/electrolyte interfaces of the electrode. This new electrode preparation process is based on an electrochemical templated synthesis of copper nanorods followed by a phosphorus vaporization. The P vapour reacts with the Cu nanorods leading to Cu3P nanorods. Preliminary electrochemical tests of the as-obtained Cu3P nanorods/Li half cell show the great interest of using such a nanostructured TMP electrode in a Li battery. These nanoarchitectured phosphide electrodes can sustain a C-rate (a full discharge in 1h) cycling without exhibiting any important reversible capacity loss for 20 cycles.

Structural and electronic modifications induced by lithium insertion in Sn-based oxide glasses

Abstract The irreversible mechanisms of lithium insertion in amorphous tin composite oxides SnB 0.6 P 0.4 O 2.9 have been studied by X-ray diffraction (XRD) and 119 Sn Mossbauer spectroscopy. The determination of the Lamb–Mossbauer factor has allowed us to evaluate the relative numbers of different tin atoms (Sn II , Sn 0 ). We show that insertion of lithium reduces the Sn II into Sn 0 atoms, which form nanoparticles of active species. The lithium ions act as glass modifiers, breaking the bonds within MOM′ (M, M′=B, P, Sn) bridges and forming non-bridging MO δ − bonds.

In situ 119Sn Mössbauer spectroscopy study of Sn-based electrode materials

Sn-based composite materials were synthetized by a conventional melt-quenching method, and studied by X-ray diffraction, electrochemistry and in situ119Sn Mösssbauer spectroscopy. Tin was dispersed ex situ into a matrix formed from B2O3:P2O5. XRD and 119Sn Mössbauer spectroscopy show the formation of an interface between the active species (Sn0) and the matrix. This amorphous interface acts as a “buffer-zone” which compensates volume changes during the tin–lithium alloy formation and avoids aggregation of tin particles.

Nanocavity Buffer Induced by Gas Ion Implantation in Silicon Substrate for Strain Relaxation of Heteroepitaxial Si1-xGex/Si Thin Layers

To weight the importance of a nanocavity buffer in a SiGe deposition substrate, some P type (001) FZ Si wafers are implanted (A samples) or not (B samples) at room temperature with 5×10 16 He + cm –2 at 10keV. They are annealed at 700°C for one hour to form a nanocavity layer close to the Si surface. Then, the wafers are carefully chemically cleaned in a clean room to remove both organic and metallic impurities from the surface. They are coated either by 210 nm (A) or 430 nm (B) Si 1−x Ge x (x=0.20±0.02) alloy grown at 575°C for 0.42 hour by low pressure chemical vapor deposition (LP-CVD) with a growth rate of 8 to 17 nm.mn −1 . Both kinds of samples are studied by cross section transmission electron microscopy, X-rays diffraction, Rutherford backscattering, atomic force microscopy and etch pit counts. The association of these techniques demonstrates that the thin SiGe layer which is deposited on sample A is fully relaxed and that the threading dislocation density (estimated to hardly reach 4×10 3 cm −2 ) is at least one order of magnitude lower than what is obtained so far using ion implantation assistance in SiGe layer growth on Silicon. The roughness of the SiGe surface is low enough to stand a further Si epitaxy. Nevertheless, the mechanism involved responsible for the threading dislocation annihilation and/or confinement is still unclear.

Characterization of Li insertion mechanisms in negative electrode materials for Li-ion batteries by Mössbauer spectroscopy and first-principles calculations

The Mossbauer spectroscopy is an efficient experimental tool to study lithium insertion mechanisms in negative electrodes of Li-ion batteries at the atomic scale. However, a quantitative interpretation of the experimental data is often difficult due to the complexity of the spectra and we propose to use first-principle calculations of the hyperfine parameters. Three different types of negative electrode materials are considered. First, the experimental 119 Sn Mossbauer spectrum obtained for the insertion of 3.5 Li into SnO is compared to the theoretical spectrum, which clearly establishes the existence of Li-Sn stable phases. Then, the analysis of the 121 Sb Mossbauer spectra for metal antimonides at the end of the first discharge shows different behaviours depending on the lithium rate. Finally, tin and iron doped titanates are considered to study changes in Ti local environments during lithium insertion.