J.P. Pereira-Ramos

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.

Synthesis by a soft chemistry route and characterization of LiNixCo1−xO2 (0 ≤ x ≤ 1) cathode materials

LiNixCo1−xO2 cathode materials have been prepared using a soft chemistry route for 0 ≤ x ≤ 1. Co-precipitation of hydroxides is followed by drying and heating at temperatures between 700 and 800 °C for a short time (2 to 5 h) under oxygen flow. Due to the high reactivity of the co-precipitates, preparation time is shorter than with powders mixing methods generally used. A DTA-TGA study has been performed for each co-precipitate. LiNixCo1−xO2 compounds show good crystallinity, but lithium deficiency appears for nickel-rich samples. LiNi0.8Co0.2O2 shows the best electrochemical charge-discharge behavior among all the nickel-cobalt compounds studied. This has been attributed to a low lithium deficiency and to a high nickel content.

High-Rate Capability Silicon Decorated Vertically Aligned Carbon Nanotubes for Li-Ion Batteries

The concept of a hybrid nanostructured collector made of thin vertically aligned carbon nanotubes (CNTs) decorated with Si nanoparticles provides high power density anodes in lithium-ion batteries. An impressive rate capability is achieved due to the efficient electronic conduction of CNTs combined with well defined electroactive Si nanoparticles: capacities of 3000 mAh g−1 at 1.3C and 800 mAh g−1 at 15C are achieved.

Birnessite manganese dioxide synthesized via a sol—gel process: a new rechargeable cathodic material for lithium batteries

In comparison with the classical birnessite compound synthesized by a conventional reaction, sol—gel lamellar birnessite having the formula MnO1.84,0.6H2O exhibits an important preferred orientation. Electrochemical Li insertion in this compound occurs in two reduction processes in both galvanostatic and voltammetric curves: the first (0 < x < 0.4) occurs between 4.25 and 2.85 V with a high kinetic transport and a strong decrease of the interlayer spacing, the second (0.4 < x < 0.9) occurs at 2.8 V with slower kinetics and no variation of the c parameter. Cycling capacity studies show that the sol—gel birnessite is the most promising rechargeable manganese dioxide with a high d.o.d. of 75% of the initial capacity (200 A h kg−1) reached after the fiftieth cycle.

Electrochemical properties of sol–gel Li4/3Ti5/3O4

Abstract The synthesis of a mixed lithium titanium spinel Li 4/3 Ti 5/3 O 4 obtained via a sol–gel process in non aqueous media is reported. The electrochemical behaviour of the sol–gel Li 4/3 Ti 5/3 O 4 spinel oxide is examined. A voltage plateau located at 1.55 V corresponds to the reversible insertion of 0.95 lithium ions in this compound while the structure is shown to be unchanged. The chemical diffusion coefficient of lithium has been evaluated by a.c. impedance: D Li is found equal to 3×10 −12 cm 2 s −1 for x =0.2 in Li (4/3+0.2) Ti 5/3 O 4 .

Electrochemical Properties of Low Temperature Crystallized LiCoO2

Electrochemical properties of low temperature (LT) crystallized LiCoO 2 are investigated. LT LiCoO 2 was obtained by a precipitation process in aqueous solution and a final heat-treatment at 400°C in air. Potentiometric, voltammetric, and ac impedance experiments are performed as well as x-ray diffraction measurements on electrochemically delithiated compounds. LT LiCoO 2 shows electrochemical and structural properties quite different from that exhibited by the high temperature (HT) LiCoO 2 . The main differences appear in terms of practical voltage, reversibility, Li transport in oxide, and structural changes as Li is deintercalated. This work clearly proves the 3D character of LT LiCoO 2 (spinel-like structure). In spite of a lower working potential and a satisfactory capacity (Δx = 0.5), the LT LiCoO 2 is highly reactive toward the electrolyte and is characterized by a slower Li transport than in layered HT LiCoO 2 .

Synthesis, ion exchange and electrochemical properties of lamellar phyllomanganates of the birnessite group

Synthesis of various X-birnessites was performed using the ion exchange properties of the sodium birnessite Na0.32MnO2,yH2O. Their structural and electro-chemical characteristics are investigated and discussed in comparison with previous data obtained for some compounds and in relation with mechanism invoked for Li electrochemical insertion into sol-gel and chemical birnessites. Two main groups of materials are obtained with a monoclinic or hexagonal structure depending on the kind of inserted cation.

Structural and Electrochemical Properties of ω ­ Li x V 2 O 5 ( 0.4 ⩽ x ⩽ 3 ) as Rechargeable Cathodic Material for Lithium Batteries

The ω-Li x V 2 O 5 phase (0.4 ≤ x ≤ 3) has been investigated as rechargeable cathodic material for lithium batteries. The interest in using the w phase as rechargeable electrode consists in the stability of its tetragonal structure (ΔV/V < 1%) as the Li insertion-extraction proceeds. Lithium ions are found to be responsible for the ordering of the structure. AC impedance measurements have shown important kinetic limitations appear in the Li composition range 2.2 ≤ x ≤ 3, hindering the use of high current densities. However, at C/20 rate a remarkable and stable specific capacity of 310 mAh g - 1 is obtained over 30 cycles. Its cycling behavior in the 3.8/1.5 V voltage window has been shown to strongly depend on the C rate and temperature. At a higher rate (C/5), the capacity decline observed as galvanostatic cycling proceeds has been found to originate from a significant dissolution process of the vanadium oxide, leading to the presence of V I V and Vm species in electrolyte.

Electrochemical properties of cathodic materials synthesized by low-temperature techniques

Abstract After having introduced the definition of ‘low temperature techniques’, the electrochemical properties of various cathodic materials (oxides) for secondary lithium batteries are reported. The influence of the way of synthesis upon their electrochemical behaviour is examined and illustrated through several examples. A presentation of electrochemical results discussed in relation with the specific chemical, physical and structural properties emphasizes the significant advances afforded by these techniques (sol-gel processes, precipitation, ion-exchange redox reactions, etc.) in obtaining new high-performance cathodic materials for secondary lithium batteries. The most interesting results are obtained for the vanadium and manganese systems.