Highly Efficient and Tunable Filtering of Electrons' Spin by Supramolecular Chirality of Nanofiber-Based Materials

Organic semiconductors and organic–inorganic 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 π-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 “up” and “down” 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 structure–property relationship for spintronic applications

Silicon/hollow γ-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 γ‑Fe₂O₃ 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 Fe­(CO)₅ with Si nanopowder and subsequent slow oxidation step in air yields hollow γ-Fe₂O₃ on the Si surface. This specific morphology results in an enhancement of the specific capacity from 2000 mAh/g_Si up to 2600 mAh/g_Si. Such a high specific capacity is achieved only for hollow γ-Fe₂O₃ 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_Si 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 organic–inorganic 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 π-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 “up” and “down” 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 structure–property relationship for spintronic applications.\u3c/p\u3