Electrospun Carbon/Cu x O Nanocomposite material as Sustainable and High Performance Anode for Lithium-Ion Batteries.

The increase in energy density of the next generation of battery materials to meet the new challenges of the electrical vehicles era calls for innovative and easily scalable materials with sustainable processes. An innovative Cu x O/C nanocomposite material, characterized by a highly conductive 3D-framework, with Cu x O/Cu-metal contiguous nanodomains is prepared by electrospinning. The electrode processing is made using a polyacrylic acid binder. The nanocomposite has been fully characterized and the electrochemical performance shows high specific capacity values over 450 galvanostatic cycles at 500 mAg-1 specific current with capacity retention values over 80 %. In addition, the composite shows remarkable high rate performance and highly stable interface, which has been studied by impedance spectroscopy.

Rational Design of Low Cost and High Energy Lithium Batteries through Tailored Fluorine-free Electrolyte and Nanostructured S/C Composite.

We report a new Li-S cell concept based on an optimized F-free catholyte solution and a high loading nanostructured C/S composite cathode. The Li2 S8 present in the electrolyte ensures both buffering against active material dissolution and Li+ conduction. The high S loading is obtained by confining elemental S (≈80 %) in the pores of a highly ordered mesopores carbon (CMK3). With this concept we demonstrate stabilization of a high energy density and excellent cycling performance over 500 cycles. This Li-S cell has a specific capacity that reaches over 1000 mA h g-1 , with an overall S loading of 3.6 mg cm-2 and low electrolyte volume (i.e., 10 µL cm-2 ), resulting in a practical energy density of 365 Wh kg-1 . The Li-S system proposed thus meets the requirements for large scale energy storage systems and is expected to be environmentally friendly and have lower cost compared with the commercial Li-ion battery thanks to the removal of both Co and F from the overall formulation.

A high-power and fast charging Li-ion battery with outstanding cycle-life.

Electrochemical energy storage devices based on Li-ion cells currently power almost all electronic devices and power tools. The development of new Li-ion cell configurations by incorporating innovative functional components (electrode materials and electrolyte formulations) will allow to bring this technology beyond mobile electronics and to boost performance largely beyond the state-of-the-art. Here we demonstrate a new full Li-ion cell constituted by a high-potential cathode material, i.e. LiNi0.5Mn1.5O4, a safe nanostructured anode material, i.e. TiO2, and a composite electrolyte made by a mixture of an ionic liquid suitable for high potential applications, i.e. Pyr1,4PF6, a lithium salt, i.e. LiPF6, and standard organic carbonates. The final cell configuration is able to reversibly cycle lithium for thousands of cycles at 1000 mAg-1 and a capacity retention of 65% at cycle 2000.

Order-Disorder Transition and Phase Separation in the MgB2 Metallic Sublattice Induced by Al Doping.

MgB2 is a superconductor constituted by alternating Mg and B planar layers: doping of both the sublattices has been observed experimentally to destroy the outstanding superconductive properties of this simple material. In this study we present the investigation by first principles methods at atomistic scale of the phase separation induced by aluminum doping in the MgB2 lattice. The calculations were performed by Density Functional Theory in generalized gradient approximation and pseudopotentials. Orthorhombic oP36 supercells derived by the primitive hR3 MgB2 cell were built in order to simulate the aluminum-magnesium substitution in the 0-50% composition range. The computational results explained the occurrence of a phase separation in the Mg1-xAlxB2 system. The miscibility gap is predicted to be induced by an order-disorder transition in the metallic sublattice at high Al concentration. Indeed at 1000 K aluminum substitution takes place on random Mg sites for concentration up to 17% of the total metallic sites, whereas at Al content larger than 31% the substitution is energetically more favorable on alternated metallic layers (Mg undoped planes alternate with Mg-Al layers). The formation of this Al-rich phase lead at 50% doping to the formation of the double omega Mg1/2Al1/2B2 ordered lattice. From 17 to 31% the two phases, the disordered Mg1-xAlxB2 (x < 0.17) and the ordered Mg1/2+yAl1/2-yB2 (y < 0.19) lattices, coexist. This phase separation is driven by the balance of the enthalpy and entropy contributions to the Gibbs energy. Present DFT-GGA calculations indicate that this thermodynamically predicted suppression of the Al doping disorder in the metallic sublattice of MgB2 occurs in parallel with the collapse of the superconductive properties of the material.

Energetics and thermodynamic stability of the mixed valence ytterbium germanides.

The results of an experimental study concerning the thermodynamic stability of the Yb germanides, described as intermediate valence compounds, complemented by a computational investigation for the Yb3Ge5 compound are reported. These compounds belong to the rare earth (RE) tetrelides (tetrel = Si, Ge, i.e., group 14 elements), a class of intermetallic materials showing unusual and promising physical properties (giant magnetocaloric effect, magnetostriction, and magnetoresistence). The high-temperature decomposition reactions of the Yb-Ge intermediate phases were studied experimentally by means of the KEMS (Knudsen effusion mass spectrometry) and KEWL (Knudsen effusion weight loss) techniques. From the reaction enthalpies derived by measuring the Yb(g) decomposition pressures as a function of temperature, the heats of formation of five out of six of the intermediate phases in the Yb-Ge system were calculated. From the computational side, the stability of the Yb3Ge5(s) compound has been investigated by DFT-LCAO-B3LYP (density functional theory-linear combination of atomic orbitals-hybrid b3lyp exchange-correlation functional) first principles calculations deriving its equilibrium geometry and the enthalpy of formation at 0 K in relation to the intermediate valence state of Yb in the lattice.

Mass spectrometric investigation of gaseous YbH, YbO and YbOH molecules.

The high-temperature gaseous molecules YbH, YbO and YbOH have been identified and their thermochemistry investigated by the Knudsen effusion mass spectrometry technique coupled with a controlled pressure gas inlet system. Solid ytterbium monosilicide and disilicide samples were made to react in the Knudsen cell with H2(g) and H2(g)/O2(g); in these conditions, several gaseous species (Yb, YbO, YbH, YbOH, SiO, SiO2, H2O) were formed under equilibrium conditions. The temperature dependences of the partial pressures of the observed gaseous molecules were analyzed to derive the Yb--X bond energies (X = H, O, OH). Selected values are D0o(Yb--H) = 179.4 +/- 2.0 kJ mol(-1), D0o(Yb--O) = 384 +/- 10 mol(-1) and D0o(Yb--OH) = 322 +/- 12 kJ mol(-1), and Delta(at)H0o(YbOH) = 746 +/- 12 kJ mol(-1). Density functional theory (DFT) calculations were also performed. Experimental and computational results are discussed and compared to previous data when available. The SiO/SiO2 high-temperature gaseous equilibrium was also observed.