15 research outputs found
Highly Efficient and Tunable Filtering of Electrons' Spin by Supramolecular Chirality of Nanofiber-Based Materials
Organic semiconductors and organicâinorganic hybrids are promising materials for spintronic-based memory devices. Recently, an alternative route to organic spintronic based on chiral-induced spin selectivity (CISS) is suggested. In the CISS effect, the chirality of the molecular system itself acts as a spin filter, thus avoiding the use of magnets for spin injection. Here, spin filtering in excess of 85% in helical Ï-conjugated materials based on supramolecular nanofibers at room temperature is reported. The high spin-filtering efficiency can even be observed in nanofibers assembled from mixtures of chiral and achiral molecules through chiral amplification effect. Furthermore and most excitingly, it is shown that both âupâ and âdownâ orientations of filtered spins can be obtained in a single enantiopure system via the temperature-dependent helicity (P and M) inversion of supramolecular nanofibers. The findings showcase that materials based on helical noncovalently assembled systems are modular platforms with an emerging structureâproperty relationship for spintronic applications
One-step synthesis of a silicon/hematite@carbon hybrid nanosheet/silicon sandwich-like composite as an anode material for Li-ion batteries
Silicon/hollow Îł-Fe2O3 Nanoberries as Efficient Anodes for Li-ion Batteries
International audienc
FeSi4P4 : A novel negative electrode with atypical electrochemical mechanism for Li and Na-ion batteries
International audienceThe electrochemical mechanism and performance of FeSi4P4, vs. Na and Li were studied using a combination of operando X-ray diffraction, 57Fe Mössbauer spectroscopy, and SQUID magnetometry. This silicon- and phosphorous-rich material exhibits a high capacity of 1750 mAh/g, retaining 1120 mAh/g after 40 cycles, and reacts through an original reversible mechanism surprisingly involving only slight changes in the chemical environment of the iron. Magnetic measurements and 57Fe Mössbauer spectroscopy at low temperature reveal the reversible but incomplete change of the magnetic moment upon charge and discharge. Such a mild reversible process without drastic phase transition (with the exception of the crystalline to amorphous transition during the first lithiation) can explain the satisfying capacity retention. The electrochemical mechanism appears thus to be significantly different from the classical conversion or alloying/dealloying mechanisms usually observed in Lithium ion batteries for p-group element based materials. The same iron silicon phosphide electrode shows also interesting but significantly lower performance vs. Na, with a limited capacity retention 350 mAh/g
Silicon/Hollow ÎłâFe<sub>2</sub>O<sub>3</sub> Nanoparticles as Efficient Anodes for Li-Ion Batteries
Nanomaterials
have triggered a lot of attention as potential triggers
for a technological breakthrough in Energy Storage Devices and specifically
Li-ion batteries. Herein, we report the original synthesis of well-defined
silicon/iron oxide nanoparticles and its application as anode materials
for Li-ion batteries. This model compound is based on earth abundant
elements and allows for a full investigation of the electrochemical
reactions through its iron oxide magnetic phase. The elaboration of
silicon with iron oxide grown on its surface has been achieved by
reacting an organometallic precursor FeÂ(CO)<sub>5</sub> with Si nanopowder
and subsequent slow oxidation step in air yields hollow Îł-Fe<sub>2</sub>O<sub>3</sub> on the Si surface. This specific morphology
results in an enhancement of the specific capacity from 2000 mAh/g<sub>Si</sub> up to 2600 mAh/g<sub>Si</sub>. Such a high specific capacity
is achieved only for hollow Îł-Fe<sub>2</sub>O<sub>3</sub> and
demonstrates a novel approach toward the modification of electrode
materials with an earth abundant transition metal like iron. This
result further emphasizes the need for precisely designed nanoparticles
in achieving significant progress in energy storage
Synthesis of Carbon Nanotubes Networks Grown on Silicon Nanoparticles as Li-Ion Anodes
Using
chemical vapor deposition, we grew carbon nanotubes (CNTs)
on the surface of Si nanoparticles (NPs) that were coated with a thin
iron shell. We studied the CNT growth mechanisms and analyzed the
influence of (1) varying annealing times and (2) varying growth times.
We show that an initial annealing is necessary to reduce the iron
oxide shell and to start the formation of Fe NPs and their consequent
coarsening. We characterize the evolution of the catalyst morphology
and its influence of the morphology and structure of the CNTs grown.
We studied this nanocomposite of Si NPs interconnected by CNTs grown
on them as anode material for Li-ion batteries. Compared to the pristine
Si NPs, the Si-CNT nanocomposite brings an increase of 40% in specific
capacity after 100 cycles at 1800 mA/g<sub>Si</sub> with a high stability
and a very low capacity loss per cycle of 0.06%. The electrochemical
performance demonstrates how efficient the CNT shell on the Si NP
is to mitigate the usual failure mechanism of Si NPs. Thus, the in
situ growth of CNTs on Si anode materials can be an efficient route
toward the synthesis of more stable Si anode composites for a Li-ion
battery
Highly efficient and tunable filtering of electrons' spin by supramolecular chirality of nanofiber-based materials
\u3cp\u3eOrganic semiconductors and organicâinorganic hybrids are promising materials for spintronic-based memory devices. Recently, an alternative route to organic spintronic based on chiral-induced spin selectivity (CISS) is suggested. In the CISS effect, the chirality of the molecular system itself acts as a spin filter, thus avoiding the use of magnets for spin injection. Here, spin filtering in excess of 85% in helical Ï-conjugated materials based on supramolecular nanofibers at room temperature is reported. The high spin-filtering efficiency can even be observed in nanofibers assembled from mixtures of chiral and achiral molecules through chiral amplification effect. Furthermore and most excitingly, it is shown that both âupâ and âdownâ orientations of filtered spins can be obtained in a single enantiopure system via the temperature-dependent helicity (P and M) inversion of supramolecular nanofibers. The findings showcase that materials based on helical noncovalently assembled systems are modular platforms with an emerging structureâproperty relationship for spintronic applications.\u3c/p\u3