New Ni0.5Ti2 (PO4)3@C NASICON-type electrode material with high rate capability performance for lithium-ion batteries: Synthesis and electrochemical properties

Ni0.5Ti2(PO4)3/C NASICON‐type phosphate is introduced as a new anode material for lithium‐ion batteries (LIBs). Ni0.5Ti2(PO4)3/C was synthesized through the sol–gel route and delivered some remarkable electrochemical performances. Specifically, the Ni0.5Ti2(PO4)3/C electrode demonstrates a high rate capability performance and delivers high reversible capacities ranging from 130 mAh g−1 to about 111 mAh g−1 at current rates ranging from 0.1 C to 5 C in the voltage window of 1.85–3 V (vs. Li+/Li). In the same voltage range, the material reaches an initial capacity of 105 mAh g−1 with a capacity retention of about 82 % after 1000 cycles at the high current rate of 10  C. The electrodes are also tested in the wider voltage range of 0.5–3 V (vs. Li+/Li) and show good reversibility and rate capability performance. Moreover, the Ni0.5Ti2(PO4)3/C electrodes enable fast Li+ diffusion (in the order of 10−13 cm2 s−1) compared with other NASICON‐type materials. As a result, a first discharge capacity of 480 mAh g−1 is reached

Vacancy ordering and electronic structure of gamma-Fe2O3 (maghemite): a theoretical investigation

The crystal structure of the iron oxide gamma-Fe2O3 is usually reported in either the cubic system (space group P4332) with partial Fe vacancy disorder or in the tetragonal system (space group P41212) with full site ordering and c/a\approx 3. Using a supercell of the cubic structure, we obtain the spectrum of energies of all the ordered configurations which contribute to the partially disordered P4332 cubic structure. Our results show that the configuration with space group P41212 is indeed much more stable than the others, and that this stability arises from a favourable electrostatic contribution, as this configuration exhibits the maximum possible homogeneity in the distribution of iron cations and vacancies. Maghemite is therefore expected to be fully ordered in equilibrium, and deviations from this behaviour should be associated with metastable growth, extended anti-site defects and surface effects in the case of small nanoparticles. The confirmation of the ordered tetragonal structure allows us to investigate the electronic structure of the material using density functional theory (DFT) calculations. The inclusion of a Hubbard (DFT+U) correction allows the calculation of a band gap in good agreement with experiment. The value of the gap is dependent on the electron spin, which is the basis for the spin-filtering properties of maghemite.Comment: 19 pages, 2 tables, 5 figures. To appear in the Journal of Physics - Condensed Matter (2010)

Schéma de valorisation des grignons d'olives produits par les maâsras marocaines

In Morroco little olive mills called “maâra” release a great quantity of olive cake in environment after extracting olive oil because there is no regulation. The chemical composition of olive cake and the important quantity released lead to environmental pollution, not acceptable with respect to the principle of sustainable development. To remedy the problem we propose a valorisation flowsheet including production of glycerin as made in other countries, and production of furfural which Morocco imports to produce lubrication oil.Au Maroc, les petites huileries artisanales appelées maâsras, après avoir extrait l'huile des olives, rejettent de grande quantité de déchets solides ou grignons dans le milieu environnemental parce qu'il n'y a pas de réglementation. La composition chimique des grignons et le fort tonnage rejeté constituent une pollution pour des régions fragiles, incompatible avec le principe du développement durable. Pour y remédier nous proposons un schéma de valorisation des grignons avec la production de glycérine qui est déjà appliquée dans d'autres pays et la production de furfural qui sert à la fabrication des huiles lubrifiantes que le Maroc importe

The T#2-Li2/3co2/3Mn1/3O2 system. 2 : Its electrochemical behavior

Electrochemical lithium deintercalation from the metastable T#2-Li2/3Co2/3Mn1/3O2 system has been investigated..

Improvement of the electrochemical performance by partial chemical substitution into the lithium site of titanium phosphate-based electrode materials for lithium-ion batteries: LiNi0.25Ti1.5 Fe0.5(PO4)3

Partial lithium substitution with nickel (0.25 of Ni2+ ion) in the previously reported Li1.5Fe0.5Ti1.5(PO4)3/C (LFTP@C) was performed to improve its structural and electrochemical properties. The new LiNi0.25Fe0.5Ti1.5(PO4)3/C (LNFTP@C) material was then tested as electrode for lithium ion batteries. In the voltage window 1.85V–3.0 V vs. Li+/Li, attractive electrochemical performances were obtained, mostly in terms of rate capability performance. At a current rate of 0.1C (6.6 mAg−1), the material delivered a capacity of around 120 mAhg−1, while at 5C, we observed a slight drop of the specific capacity reaching a value of 108 mAhg−1. Long-term cycling performance stability was also tested demonstrating a remarkable capacity decrease during the last 500 cycles. The capacity retention decreased from 94% to 91% after 500 cycles to about 77% and 74% after 1000 cycles at fast current rates of 5C (329.8 mAg−1) and 10C (659.6 mAg−1), respectively. In the wider voltage window, an average specific capacity of around 380 mAhg−1 was attained at a slow current rate of 0.1C

Analysis of trapping effects on the forward current-voltage characteristics of al-implanted 4H-SiC p-i-n Diodes

The forward current-voltage characteristics (IF-VF) of aluminum (Al)-implanted 4H-SiC p-i-n diodes are investigated by means of a numerical simulation study that takes into account both intrinsic and doping-induced deep defects, namely, the Z1/2 and EH6/7 centers inside the drift region and an electrically active trap concentration inside the anode region due to the Al+ ion implantation process. From the experimental results, the fundamental electric parameters of several samples were extracted at different regions of diode operation and used for comparison. The modeling analysis reveals that Z1/2 and EH6/7 centers reduce the effective carrier lifetimes and increase the recombination rate in the drift region determining the slope of the IF curve in the recombination and diffusion regimes. In addition, a defect density that becomes comparable to the epilayer doping concentration introduces an apparent shunt resistance effect at low-medium biases and at the same time has a noticeable impact on the diode series resistance at voltages higher than 2.7 V. A detrimental effect on the series resistance is also observed in dependence of the trap concentration in the anode region that increases the diode's internal resistance as a consequence of the carrier mobility decrease. Above the IF curve knee, the diode current is largely dominated by the electron injection into the anode since the concentration of free holes for conduction is strongly limited in turn by the incomplete activation of the ion-implanted impurities and the trap activity