G.A. Nazri

Metal hydrides for lithium-ion batteries

Classical electrodes for Li-ion technology operate via an insertion/de-insertion process. Recently, conversion electrodes have shown the capability of greater capacity, but have so far suffered from a marked hysteresis in voltage between charge and discharge, leading to poor energy efficiency and voltages. Here, we present the electrochemical reactivity of MgH(2) with Li that constitutes the first use of a metal-hydride electrode for Li-ion batteries. The MgH(2) electrode shows a large, reversible capacity of 1,480 mAh g(-1) at an average voltage of 0.5 V versus Li(+)/Li(o) which is suitable for the negative electrode. In addition, it shows the lowest polarization for conversion electrodes. The electrochemical reaction results in formation of a composite containing Mg embedded in a LiH matrix, which on charging converts back to MgH(2). Furthermore, the reaction is not specific to MgH(2), as other metal or intermetallic hydrides show similar reactivity towards Li. Equally promising, the reaction produces nanosized Mg and MgH(2), which show enhanced hydrogen sorption/desorption kinetics. We hope that such findings can pave the way for designing nanoscale active metal elements with applications in hydrogen storage and lithium-ion batteries.

Electrochemical performances of layered LiM1-yMy'O2 (M = Ni, Co; M' = Mg, Al, B) oxides in lithium batteries

Abstract Electrochemical performances of substituted layered oxides LiM 1− y M y ′O 2 (M=Ni, Co and M′=Mg, Al, B) as cathode materials in lithium batteries have been investigated. These materials have been made through a solid state reaction of precursors in an oxygen rich atmosphere. X-ray diffraction and infrared measurements have been carried out. Structural data have shown that a single phase, impurity free, can be made through careful selection of precursors, except for the B substituted compounds, for which residual impurity phases were observed due to a more glassy nature of the products. The voltage profiles of the layered oxides and substituted oxides were monitored against a lithium electrode. The overall capacity of the oxides have been reduced due to the sp metal substitution, however, a more stable charge–discharge cycling performance has been observed when electrodes are charged to 4.3 V as compared to the performances of the native oxides. At the cut-off voltage of 4.4 V, the charge capacity of the Li//LiNi 0.95 Al 0.05 O 2 cell is ca. 165 mAh/g. Boron doped LiCoO 2 also provides very low polarization during charge–discharge cycling, with a capacity over 130 mAh/g when charged up to 4.3 V versus a lithium anode. A sample of LiNiO 2 with 5% Mg substitution delivers a capacity of 168 mAh/g.

Vibrational spectroscopy and electrochemical properties of LiNi0.7Co0.3O2 cathode material for rechargeable lithium batteries

We are reporting the synthesis and characterization of solid solutions of the LiNiO2 and LiCoO2 system. Substitution of cobalt for nickel in the LiNi1−yCoyO2 phases provides significant improvements in the two-dimensionality of the crystal lattice and ease the large scale synthesis. This structural effect improves the reversibility of the lithium intercalation-deintercalation process. We have evaluated the vibrational spectra and electrochemical properties of LiNi0.7Co0.3O2 (charge-discharge profiles and cyclic voltammetry) and compared the results with those of the end members, i.e., LiNiO2 and LiCoO2. The local environment of cations against oxygen neighboring atoms has been determined.

Vibrational Spectroscopic Studies of the Local Environment in 4-Volt Cathode Materials

The authors report the vibrational spectra of numerous 4-volt cathode materials, the transition metal oxides which are potential materials for advanced Li-ion batteries. They provide high specific energy density, high voltage, and remarkable reversibility for lithium intercalation-deintercalation process. Studies were carried out by Raman and FTIR spectroscopies. Oxides such as LiMn{sub 2}O{sub 4}, LiNiVO{sub 4}, LiCoVO{sub 4} spinels, LiMeO{sub 2} (Me=Co, Ni, Cr) layered compounds and their mixed compounds have been investigated. The local environment of cations against oxygen neighboring atoms has been determined by considering tetrahedral and octahedral units building the lattice. Structural modifications induced by the intercalation-deintercalation process, by the cation substitution, or by the low-temperature preparation route are also examined. The results are compared with those of end members.

Synthesis, Structure, Lattice Dynamics and Electrochemistry of Lithiated Manganese Spinel, LiMn2O4

We report synthesis, crystal structure, lattice dynamics, and electrochemical features of the lithiated manganese oxide spinel prepared through solid state reaction by careful selection of precursors and synthesis conditions. Elemental analysis shows that the material is a lithium-rich spinel phase. X-ray diffraction data and Rietveld refinement indicate formation of a single phase, impurity free, normal spinel of LiMn 2 O 4 . Lattice dynamics have been investigated by vibrational spectroscopy and group theoretical analysis has been carried out. Electrochemical performances of the lithiated spinel manganese oxide have been investigated, and the voltage profile of the cathode during lithium intercalation-deintercalation processes, close to equilibrium, has been obtained. The upper 4-volt plateau provides over 130 mA h/g with an excellent cyclability.

Vibrational Spectroscopy of Lithium Manganese Spinel Oxides

Abstract Lithiated spinel manganese oxides with various amounts of lithium have been prepared through solid-state reaction and electrochemical intercalation and deintercalation. Structures of the LixMn2O4 samples with 0.3≤x≤1.2 are studied using X-ray diffraction and Rietveld refinement techniques. We report vibrational spectra of lithiated manganese oxides as a function of lithium concentration. The spectra of lithiated spinel manganese oxides have been analyzed on the basis of LiO4 tetrahedra and MnO6 octahedra when Li/Mn≤0.5, and LiO4, LiO6, and MnO6 structural units when Li/Mn>0.5. Electrochemical performances of lithium manganese oxide are also studied.

Enhanced hydrogen sorption capacities and kinetics of Mg2Ni alloys by ball-milling with carbon and Pd coating

Solid-state hydrogen storage alloys are becoming a practical method to transport and utilize hydrogen as fuel for various technologies. In this paper, the kinetics and capacity of hydrogen desorption from Mg-based alloys have markedly been enhanced by tuning the surface composition of alloy particles. Mg 2 Ni-C 1 . x composites (where t refers to the pregrinding time and x to the Brunauer-Emmet-Teller specific surface area) were prepared by ball-milling the alloy in the presence of preground graphite, and Pd-coated Mg 2 Ni alloy powders were obtained by controlled chemical deposition of Pd on the alloy surface. We have found that the optimization of the pregrinding step of carbon is a determinant factor in enhancing the hydrogen desorption capacity of the Mg 2 Ni-10 wt.% C 1 0 . 3 2 0 composites to 2.6 wt.% at 150 °C, the maximum performance so far reported on desorption for Mg-based alloys. Such value can even be raised to 2.8 wt.% by applying Pd deposition on the composite.

Enhancement of hydrogen storage in MgNi by Pd-coating

Abstract MgNi alloys prepared by mechanical alloying were coated with Pd nanoparticles via a polyol process. Such a process allows the deposition of fine particles of metal catalysts on the MgNi alloy surface. This surface modification leads to a strong improvement of the H storage performances of the alloy. The hydrogen release at 150xa0°C increases from 0.6 wt.% for uncoated MgNi alloy to 1.5 wt.% for a 5 wt.% Pd-coated MgNi alloy. The strong enhancement of the desorption capacity probably results from the catalytic effect of Pd, which may act as a hydrogen pump, thus favoring hydrogen migration from the bulk to the surface of the alloy.

General Overview of Vibrational Spectroscopy of Layered Transition-Metal Oxides

We report the vibrational spectra of various layered transition-metal oxides, which are potential cathode materials for advanced Li-ion batteries. They provide high specific energy density, high voltage, and remarkable reversibility for lithium intercalation-deintercalation process. Studies were carried out by Raman and FTIR spectroscopies. Oxides such as LiMO 2 (M=Co, Ni, Cr) layered compounds and their mixed compounds have been investigated. The local environment of cations against oxygen neighboring atoms has been determined by considering polyhedral units building the lattice. Structural modifications induced by intercalation-deintercalation process, by cation substitution, or by low-temperature preparation route are examined.

Electrochemical behavior of hydrated molybdenum oxides in rechargeable lithium batteries

Oxide-hydrates of molybdenum (OHM) are investigated as 3-volt cathode materials for rechargeable lithium batteries. These materials with different water content showed a much better performance than that of MoO3 as cathode of the rechargeable lithium battery. We report the electrochemical characteristics of Li//OHM batteries using the oxides and oxide-hydrates of molybdenum which were synthesized from molybdic acid. The oxide has a corrugated layered structure consisting of corner-shared MoO6 octahedra. This structure provides electronic conductivity within basal layer and high lithium ion mobility between layers. The mechanism of dehydration and structural rearrangement of molybdic acid during heat treatment were studied by thermal analysis, x-ray diffraction, and Raman spectroscopy. Thermal analysis indicates a two-step dehydration and formation of orthorhombic α-MoO3 and monoclinic ß-MoO3. Discharge profiles and kinetics are dependent on the amount of “structural water” into the host lattice. The electroinsertion of Li ions occurs mainly in two steps in the potential range between 3.0 and 1.5 V (compositional range 0.0≤x(Li)≤1.5).