R. Baddour-Hadjean

Raman Microspectrometry Applied to the Study of Electrode Materials for Lithium Batteries

4.3. Manganese Oxide-Based Compounds 1291 4.3.1. MnO2-Type Compounds 1291 4.3.2. Ternary Lithiated LixMnOy Compounds 1293 4.4. Vanadium Pentoxide V2O5 1298 4.4.1. V2O5 Structure 1298 4.4.2. LixV2O5 Bulk Phases 1300 4.4.3. LixV2O5 Crystallized Thin Films 1303 4.5. Titanium Oxide-Based Compounds 1305 4.5.1. Lithium Titanate Li4Ti5O12 1306 4.5.2. TiO2 Anatase 1308 5. Phospho-olivine LiFePO4 Compound 1312 6. General Conclusion 1314 7. Acknowledgments 1315 8. References 1315

Raman spectra of birnessite manganese dioxides

Structural features of layered manganese dioxides of the birnessite family are studied using Raman scattering spectroscopy. This local probe is capable of analysing directly the near-neighbour environment of oxygen coordination around manganese and lithium cations. Four types of sol–gel birnessite (SGB) are considered: lithium birnessite (Li-Bir), sodium birnessite (Na-Bir), sol–gel birnessite (SG-Bir), and sol–gel Co-doped birnessite (SGCo-Bir). Thus, in a first approach, we consider the overall spectral features of birnessites such as the superposition of the spectra of local structures, while the lattice modes are discussed in the spectroscopic symmetry. Results show the specific spectroscopic fingerprints of SG-Bir single phases, the site occupancy of Co ions in the substituted SGCo-Bir compound, and vibrations due to lithium ions with their oxygen neighbours in Li-Bir, Li0.32MnO2·0.6H2O. A correlation between the interlayer d-spacing and the stretching mode frequencies of birnessite oxides has been established.

Vibrational modes in layered double hydroxides and their calcined derivatives

Abstract Vibrational modes of layered double hydroxides and their calcined derivatives in the region of 60–4000 cm −1 have been studied using a combination of inelastic neutron scattering (INS), Fourier transform infrared (FTIR) and Raman spectroscopies. The INS spectra recorded at 30 K are dominated by the vibrational contribution of the water contained in the negatively charged layers. Using FTIR and Raman assignments of LDHs and magnesium hydroxide, the lattice modes of the moieties present in the positively charged layers have been identified and assigned. We infer from the results that the vibrational modes of the cationic layer are unaffected by change in the identity of the interlayer anions and that the hydroxyl bonds are strengthened by thermal activation.

Lattice Dynamics of β-V2O5: Raman Spectroscopic Insight into the Atomistic Structure of a High-Pressure Vanadium Pentoxide Polymorph

We report here the Raman spectrum and lattice dynamics study of a well-crystallized β-V(2)O(5) material prepared via a high-temperature/high-pressure (HT/HP) route, using α-V(2)O(5) as the precursor. Periodic quantum-chemical density functional theory calculations show good agreement with the experimental results and allow one to assign the observed spectral features to specific vibrational modes in the β-V(2)O(5) polymorph. Key structure-spectrum relationships are extracted from comparative analysis of the vibrational states of the β-V(2)O(5) and α-V(2)O(5) structures, and spectral patterns specific to the basic units of the two V(2)O(5) phases are proposed for the first time. Such results open the way for the use of Raman spectroscopy for the structural characterization of vanadium oxide-based host lattices of interest in the field of lithium batteries and help us to greatly understand the atomistic mechanism involved in the α-to-β phase transition of vanadium pentoxide.

The peculiar structural behaviour of β-Na0.33V2O5 upon electrochemical lithium insertion

The structural behaviour of the β-Na0.33V2O5 active material in a composite electrode is determined during discharge in the 3.8/2.2 V potential range (0 ≤ x < 1.66 in LixNa0.33V2O5) using X-ray diffraction combined with Raman microspectrometry. In spite of the existence of three well defined voltage plateaus, we provide evidence here for very weak structural changes throughout the lithium intercalation process, both at the long range order and local scale, involving mainly minor unit cell parameter variations. This result contrasts with the sharp phase transitions with one-phase and large two-phase regions usually observed for Li intercalation compounds exhibiting successive voltage plateaux separated by potential drops. The present findings demonstrate the reliability of a lithium filling scheme in the β-Na0.33V2O5 3D host lattice involving no phase transition in a remarkably wide Li composition range. Furthermore, new kinetic data for the electrochemical Li insertion reaction into β-Na0.33V2O5 are reported using AC impedance spectroscopy, which are discussed in relation with the specific structural response. This peculiar behaviour highlights the interest of such rigid tunnel framework to minimize the structural stress induced by lithium insertion.

High-Performance Oriented V2O5 Thin Films Prepared by DC Sputtering for Rechargeable Lithium Microbatteries

Crystalline thin films of vanadium pentoxide have been deposited by dc sputtering using a vanadium target. Depending on the power applied, two set of samples 800 nm thick characterized by a 001 or an h00 preferred orientation have been synthesized. Investigation of their respective electrochemical properties as positive electrode for rechargeable lithium microbatteries has been performed in liquid electrolyte. The h00 oriented deposits exhibit a better electrochemical behavior in terms of rate capability, polarization, and cycling properties in the voltage range 3.8/2.8 V. Specific capacities of 25 and 40 μAh/cm 2 are recovered after 50 cycles at 10 μA/cm 2 in the potential windows 3.8/2.8 and 3.8/2.15 V, respectively. A better electronic conductivity combined with a high porosity induced by a specific morphology are thought to be responsible for this attractive behavior. X-ray diffraction experiments clearly indicate Li insertion results in a continuous increase of the interlayer distance c and a contraction of the a parameter with x in Li x V 2 O 5 (0 < x < 1) without the emergence of the 8 phase as expected in the bulk material. Using the same procedure, a 2.4 μm thick V 2 O 5 film has been prepared with the h00 preferred orientation to optimize the cycling performance. An excellent rechargeability has been proved in the voltage range 3.8/2.8 V because a specific capacity of 70 μAh/cm 2 is still available at a high current density of 100 μA/cm 2 , showing a good kinetic behavior and a good adherence to the substrate. The present study suggests very thick h00-oriented V 2 O 5 deposits can be prepared with high specific capacities and long cycle life.

High-Capacity Crystalline V2O5 Thick Films Prepared by RF Sputtering as Positive Electrodes for Rechargeable Lithium Microbatteries

We demonstrate that crystalline V 2 O 5 thick films up to 3.6 μm thick can be synthesized by radio frequency (rf) sputtering using a vanadium target and without any postannealing treatment. Crystalline deposits in the range 0.6-3.6 μm thick exhibit a rough surface morphology and a high porosity, allowing the electrolyte to penetrate the active material. The discharge-charge properties of the films are investigated in the two voltage windows 3.8/2.8 V and 3.8/2.15 V as a function of the thickness. We clearly show that such films allow one to get high specific capacities between 20 and 120 μAh/cm 2 in the 3.8/2.8 V range, depending on the thickness, even at a high rate of 8 C and between 40 and 250 μAh/cm 2 in the 3.8/2.15 V range. The influence of the current density indicates a little change in the capacity and the polarization, showing the homogeneous and efficient behavior of these sputtered films, in spite of their thickness, which can reach 3.6 μm. The capacity is found to be a linear function of the thickness with a similar slope from the C/15 rate to the 8 C rate. The cycling behavior of these cathode film materials is attractive with, for instance, a high and stable capacity of 100 μAh/cm 2 after 90 cycles at 0.1 mA/cm 2 at high voltage for the 3.6 μm thick film and a capacity of 150 μAh/cm 2 found to be stable from the 50th cycle in the 3.8/2.15 V range at 1 mA/cm 2 (8 C). The capacity fading observed after all of the first cycles in the potential limits 3.8/2.8 V and that found when the three insertion steps are involved is discussed in terms of structural data and impedance behavior.

A kinetic study of lithium transport in a new Li intercalation material Al{sub 0.11}V{sub 2}O{sub 5.15} synthesized via a sol-gel process

The main electrochemical characteristics of a new aluminum vanadium oxide synthesized via a sol-gel process are reported. The kinetics of the electrochemical insertion of lithium into Al{sub 0.11}V{sub 2}O{sub 5.15} has been investigated using ac impedance spectroscopy and the pulse relaxation technique. These two methods, which involve basically different kinds of perturbation and measurement, provide similar data. The variation of the chemical diffusion coefficient {tilde D}{sub Li}, in the range 10{sup {minus}10} to 10{sup {minus}11} cm{sup 2}/s{sup {minus}1}, as a function of the Li content, is compared to that previously obtained for the V{sub 2}O{sub 5} parent oxide and tentatively correlated with previous structural data reported on V{sub 2}O{sub 5} and orthorhombic mixed oxides M{sub y}V{sub 2}O{sub 5} (M = Fe{sup 3+}, Al{sup 3+}).

A comparative insight of potassium vanadates as positive electrode materials for Li batteries: influence of the long-range and local structure.

Potassium vanadates with ratio K/V = 1:3, 1:4, and 1:8, prepared by a fast and facile synthesis route, were investigated as positive electrode materials in lithium batteries. KV3O8 and K0.5V2O5 have layered structures, while K0.25V2O5 exhibits a tunnel framework isomorphic to that of β-Na0.33V2O5. The Raman spectra of KV3O8, K0.5V2O5, and K0.25V2O5 compounds are reported here for the first time, and a detailed comparative analysis distinguishes spectral patterns specific to each structural arrangement. The electrochemical performances of these potassium vanadates toward lithium insertion were investigated. The potassium-richer compound KV3O8 shows a good rechargeability in spite of a low discharge capacity of 70 mAh g(-1), while the potassium-poorer bronze K0.25V2O5 exhibits the highest specific capacity of 230 mAh g(-1) but a slow and continuous capacity fade with cycling. We demonstrate that the K0.5V2O5 compound, with its double-sheet V2O5 layered framework characterized by a large interlayer spacing of 7.7 Å, is the best candidate as positive electrode for lithium battery among the potassium-vanadium bronzes and oxides. A remarkable specific capacity of 210 mAh g(-1), combined with excellent capacity retention, is achieved.

New ternary intermetallic compounds belonging to the R–Y–Ni (R=La, Ce) system as negative electrodes for Ni–MH batteries

Abstract New ternary yttrium-based alloys with general formula La 1− x Ce x Y 2 Ni 9 (0≤ x ≤1) have been synthesized and the influence of cerium substitution on the structural, thermodynamic and electrochemical properties is discussed. The hydrogen absorption–desorption properties are consistent with the application as negative electrode materials in alkaline medium. The electrochemical study shows promising results for 0≤ x ≤0.5 compositions in terms of hydrogen storage applications.