Showing papers by "Christian M. Julien published in 2013"

Advanced Electrodes for High Power Li-ion Batteries.

Abstract: While little success has been obtained over the past few years in attempts to increase the capacity of Li-ion batteries, significant improvement in the power density has been achieved, opening the route to new applications, from hybrid electric vehicles to high-power electronics and regulation of the intermittency problem of electric energy supply on smart grids. This success has been achieved not only by decreasing the size of the active particles of the electrodes to few tens of nanometers, but also by surface modification and the synthesis of new multi-composite particles. It is the aim of this work to review the different approaches that have been successful to obtain Li-ion batteries with improved high-rate performance and to discuss how these results prefigure further improvement in the near future.

MnO2 Nano-Rods Prepared by Redox Reaction as Cathodes in Lithium Batteries

Abstract: α- and β-MnO2 phases have been synthesized by redox reaction of ammonium persulphate with manganese sulphate and manganese nitrate. A single phase of α-MnO2 was observed for the sample prepared from manganese sulphate, while β-MnO2 phase was obtained from manganese nitrate. Characteristic bands of hollandite and rutile phase were observed by FTIR. Nanorods structures were observed by images of transmission electron microscopy for both samples. Good electrochemical performance was observed for β-MnO2, which yields a specific discharge capacity of 180 and 130 mAh g−1 in the first and 45th cycle respectively. The specific discharge capacity of α-MnO2 is ca. 210 mAh g−1 at first cycle that decreases to 115 mAh g−1 in the 45th cycle.

Dynamics of polaron formation in Li 2 O 2 from density functional perturbation theory

Abstract: Additional electrons injected into lithium peroxide become self-trapped to form polarons. While the final stage of this self-trapping phenomenon has been examined extensively, the electron-phonon interactions that drive this process remain largely unaddressed in the first-principles literature. In order to understand the dynamical process of polaron formation in lithium peroxide, we examine the initial embryonic stage of this process through first-principles calculations of the electron-phonon interaction between the lithium peroxide lattice and an extra electron injected into the crystal. It is shown that the electron-phonon interaction is perceivably strong with such phonons whose vibration patterns map directly onto the lattice distortions that occur when a polaron is actually formed. These patterns indicate the elongation of the bond length of the O${}_{2}^{2\ensuremath{-}}$ ions and contraction of the surrounding Li${}^{+}$ ions.

Dynamics of polaron formation in Li2O2 from density functional perturbation theory

Abstract: Additional electrons injected into lithium peroxide become self-trapped to form polarons. While the nal stage of this self-trapping phenomenon has been examined extensively, the electron-phonon interactions that drive this process remain largely unaddressed in the rst principles literature. In order to understand the dynamical process of polaron formation in lithium peroxide, we examine the initial embryonic stage of this process through rst principles calculations of the electron-phonon interaction between the lithium peroxide lattice and an extra electron injected into the crystal. It is shown that the electron-phonon interaction is perceivably strong with such phonons whose vibration patterns map directly onto the lattice distortions that occur when a polaron is actually formed. These patterns indicate the elongation of the bond length of the O2 2 ions and contraction of the surrounding Li+ ions.

Surface and Bulk Properties of LiFePO4: The Magnetic Analysis

Abstract: The magnetic properties of LiFePO4 particles are reviewed. Their analysis is a very efficient tool of characterization of the intrinsic properties of the bulk material. They are also used to identify and determine the concentration of the impurities and of the defects, separately. They are also used to characterize the surface layer, study its crystallinity, and its delithiation upon exposure to moisture.

LiMnyFe1-yPO4 (0.5≤y≤0.8) Cathode Materials Grown by Hydrothermal Route: Electrochemical Performance

Abstract: We report the electrochemical properties of LiMnyFe1-yPO4 (0.5≤y≤0.8) cathode materials synthesized by hydrothermal route. Special attention was taken to optimize the carbon deposit on the surface of particles in order to make easy comparison of the electrochemical performance as a function composition with the same particle size. The substitution led to the modification of the electrochemical performance, such as initial capacity, capacity fading and polarization. We present the modified Peukert diagrams for C-rate in the range from C/12 to 40C.

Orthorhombic MoO3 Nanofibers as Cathode Materials for Lithium Batteries

Abstract: We report the structural and electrochemical properties of MoO3 nanofibers synthesized by hydrothermal reaction from acidified ammonium heptamolybdate tetrahydrate precursor. Structural analysis shows that MoO3 nanofibers 50-80 nm in diameter and a several micrometers in length are grown in the orthorhombic system (Pbnm S.G.). The composition MoO2.9975 was determined by Rietveld refinement and magnetic susceptibility measurements. The electrochemical performance of Li//MoO3 cells with nanofibers deliver a better discharge capacity after 40 cycles than MoO3 bulk.

Carbon-Coated Nano-Structured MoO3 as Cathode Materials for Lithium Batteries, Synthesis, Structure and Electrochemical Performance

Abstract: We report the synthesis of carbon-coated α-MoO3 nano-materials and their structural and electrochemical properties. The carbon deposit performed by the lactose method allows enhancement of the electronic conductivity of the composite. The structure of the carbon film is investigated by Raman spectroscopy. The electrochemical tests were carried out in Li/LiPF6-EC- DEC/MoO3 cells. The charge-discharge reaction is investigated as a function of C-rate and the influence of electrode preparation on the electrochemical performance was examined.