M. Massot

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.

Lattice vibrations of materials for lithium rechargeable batteries I. Lithium manganese oxide spinel

Abstract Raman scattering (RS) and Fourier transform infrared (FTIR) spectroscopy have been applied to the study of local structure of lithium manganese oxides. We report the analysis of the vibrational spectra of spinel LiMn 2 O 4 structure using both the classical group factor analysis ( O h 7 ) and a local environment model. The RS and FTIR spectra are analysed on the basis of LiO 4 tetrahedra and MnO 6 octahedra building the lattice. RS and FTIR line intensities and positions remained in good agreement with the Fd 3 m space group. Isotopic substitution of 6 Li for 7 Li leads the conclusion that the spectral features of the LiO 4 remains in the 350–400 cm −l and the vibrational modes of the MnO 6 expand over 450–650 cm −l . Vibrational spectra of the lithium-rich manganese oxide spinels are also presented for comparison with the λ-LiMn 2 O 4 phase.

Raman and infrared spectroscopic studies of GeGaAg sulphide glasses

Gallium sulphide forms stable glasses with GeS2 over a wide range of composition, and in the same system complex materials are obtained by dissolving silver sulphide. In such glasses Ga2S3 acts as a co-former with GeS2 whereas Ag2S plays the role of modifier. Raman scattering and infrared absorption measurements have been carried out on the Ge2S4Ga2S3Ag2S glass system. The structural arrangement of these glasses is studied as a function of the composition in the ternary glass-forming region. The vibrational assignment is made mainly in terms of bridging and non-bridging sulphur in the vitreous network. The tendency of gallium atoms to form GaS4 tetrahedra forces germanium atoms to induce the formation of S3GeGeS3 structural groups due to the shortage of sulphur atoms. When Ag2S is associated with Ge2S4Ga2S3 glasses, its defavors the edge-shared GeS4 tetrahedra and contributes to the cohesion of corner-shared tetrahedra. When Ag2S content increases, we observe a band located at low frequency that we have attributed to charge-coupled silver cation motion. A slight distortion of the tetrahedral groups is also seen from the vibrational features.

Structural and vibrational studies of LiNi1−yCoyVO4 (0≤y≤1) cathodes materials for Li-ion batteries

Abstract The structure and vibrational properties of high voltage cathode materials, namely LiNi 1−y CO y VO 4 solid solution with (0≤y≤1), have been studied using X-ray diffraction, Raman scattering and FTIR measurements. Rietveld refinements show that LiNi 1− y Co y VO 4 vanadates belong to the inverse spinel structure with Fd 3 m(O 7 h ) space group. Analysis of Raman spectra has been carried out in the molecular approximation using a local environment model including VO 4 tetrahedra, (Ni, Co)O 6 and LiO 6 octahedra as vibrational local units.

Infrared studies of the structure of borate glasses

Abstract Infrared spectroscopy investigations of binary glasses B 2 O 3  xLi 2 O with 0 x 1 have been performed in order to understand the glass-modifying properties of Li 2 O. The mid-reflectivity spectra show clearly the disappearance of boroxol rings and the formation, in a first step, of tetraborate groups and later of diborate groups as the oxide content increases. For high values of ξ, borate groups with non-bridging oxygen atoms are formed. One band at about 390 cm −1 is attributed to vabration of the lithium ions. Modifications of the boron-oxygen network with the addition of lithium sulphate as a doping salt have also been investigated in the ternary system B 2 O 3  xLi 2 OyLi 2 Si 4 . At the same time, by far-infrared absorption on the binary glass, the vibrational motion of the lithium cations has been confirmed.

Density and ultrasonic velocities in fast ionic conducting borate glasses

The density and the sound velocities have been measured at room temperature in the ternary borate glasses, B2O3−xLi2O−yLinX (n=1 for X=F, Cl, Br and I; and n=2 for X=SO4), as a function of the concentration for the different ‘doping’ salts (LinX). Two series of ternary glasses with different O/B ratios, x=0.2 and 0.6, have been studied. In both series, a structural model where the anion of the ‘doping’ salts are located in interstitial positions inside the boron–oxygen network is used to explain the experimental results in borate glasses ‘doped’ with LiCl, LiBr and LiI. In the case of glasses ‘doped’ by LiF or Li2SO4, there is evidence of a direct participation of the salt anions to the boron–oxygen network. A structural modification is proposed for the LiF-‘doped’ borate glasses with x=0.2 and 0.6. Changes in the medium-range order induced by the addition of ‘doping’ salts are also discussed in these ternary glasses.

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.

Soft-chemistry synthesis of electrochemically-active spinel LiMn2O4 for Li-ion batteries

Abstract Battery grade spinel-LiMn 2 O 4 cathode-active material has been synthesized through a soft-chemistry aided low temperature precursor process. It has been found that the bulk quantities of submicron-sized spinel-LiMn 2 O 4 powders can be obtained at a modest temperature as low as 300°C, with the highest level of phase purity without any residual impurities. This technique describes a simple solution mixing procedure in the presence of a complexing agent, preferably a carboxylic acid, namely succinic acid. The details of the synthesis procedure are presented and the physical properties of the synthesized spinel are discussed in the light of structural (XRD), spectroscopic (IR and Raman), and thermal (DTA/TG) techniques. The electrochemical test cells (coin-type) containing the synthesized spinel oxide as positive electrode in conjunction with either lithium metal or carbonaceous (graphite) anode employing a nonaqueous organic electrolyte mixture of 1 M LiPF 6 in EC+DMC+MF show an improved performance in terms of its capacity and cyclability over extended cycles.

Lattice vibrations of materials for lithium rechargeable batteries V. Local structure of Li0.3MnO2

Abstract We report the structural properties of Li 0.3 MnO 2 positive electrode materials for secondary lithium batteries. The crystal structure examined by X-ray diffraction corresponds to a new MnO 2 with an ordered alternation of (1×2) and (1×1) channels of the γ-MnO 2 phase. The vibrational properties studied by Raman scattering (RS) and Fourier transform infrared (FTIR) spectroscopy as local probes show that lithium ions are located in octahedral sites in the (1×2) channels. Significant changes are seen in the MnO 6 octahedral arrangement from sample to sample by examining the spectra in high-frequency region compared with their parents that are pyrolusite and ramsdellite manganese dioxides. The cycling behavior of the Li 0.3 MnO 2 electrode exhibits a practical material utilization capacity of 155 mA h g −1 over 60 cycles.

Structure of borovandate glasses studied by Raman spectroscopy

Borovanadate glasses (1−x)[B2O3–yLi2O]–xV2O5 with 0≤x≤1 and 0≤y≤1 have been prepared and systematically studied by Raman spectroscopy. The results have been compared with glass transition temperature measurements. The Raman spectra exhibit a characteristic band at about 900 cm−1 whose shape and frequency are dependent on both V2O5 and Li2O concentration. The study of the line shape has shown that vanadium–oxygen structural units formed in the glasses are VO4 tetrahedra and VO5 pyramids according to the Li2O content. It is also observed that V2O5 behaves as modifier or as glass former in regard to the boron–oxygen network.