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Abstract: Raman scattering spectra have been investigated to evaluate the local structure of lithiated oxides used as electrode materials for lithium-ion batteries. We report the analysis of the vibrational spectra of ordered spinel phases including the partially delithiated λ-Li0.5Mn2O4 ( SG), the partial charge-ordered LiMn2O4 orthorhombic form (Fddd SG) and the LiNi0.5Mn1.5O4 substituted oxide (P4132 SG). Analysis of spectroscopic data is performed using the classical factor group theory and the vibration features are compared with those of the ordered lithium ferrite α-LiFe5O8 and the normal spinels LiMn2O4 and LiNi0.5Mn1.5O4 (Fd3m SG), and the inverse spinel LiNiVO4. [Copyright &y& Elsevier]

Abstract: We present the synthesis, characterization and electrode behaviour of LiMn2−y Co y O4 (0≤ y ≤1) spinel oxides prepared by the wet-chemical route assisted by carboxylic acid. The phase evolution was studied as a function of the cobalt substitution and the modification on the intercalation and deintercalation of Li ions. Characterization methods include TG-DTA, XRD, SEM, Raman, FTIR, and SQUID. LiMn2−y Co y O4 samples crystallize with the cubic spinel-like structure (Fd3m S.G.). Raman scattering and FT-infrared spectroscopy indicate that the vibrational mode frequencies and relative intensities of the bands are sensitive to the covalency of the (Co, Mn)–O bonds. MEB micrographs show that the particle dimension of the LiMn2−y Co y O4 powders ranges in the sub-micron-sized domain with a narrow grain-size distribution. The overall electrochemical capacity of LiMn2−y Co y O4 oxides have been reduced due to the 3d6 metal substitution. However, a more stable charge–discharge cycling performances has been observed when the electrodes are charged up to 4.3V as compared to the performance of the native oxide. For such a cut-off voltage, the charge capacity of the Li//LiMn1.8Co0.2O4 cell is ca. 101mAh/g. Differences and similarities between LiMn2O4 and Co-substituted oxides are discussed there from. [Copyright &y& Elsevier]

Abstract: We present the magnetic properties of LiNi0.5Mn1.5O4 spinels prepared by the sol–gel and pyrolysis techniques. Structural properties show that the material synthesized by pyrolysis method exhibit an ordered spinel structure. Characterization methods include SQUID magnetometry and ESR spectroscopy. Magnetic measurements have evidenced the ferromagnetic ordering below in LiNi0.5Mn1.5O4. Results show that actually no impurity phase is detected in LiNi0.5Mn1.5O4, thus the ferrimagnetic behavior is attributed to an intrinsic property of this material. The magnetic order in this case is trivially a collinear ferrimagnetic ordering in which both the Ni sublattice and the Mn sublattice are ferromagnetic. ESR measurements show a two-component signal with a complex shape. The dominant band is assigned to Mn4+ ions that are the only paramagnetic entities in this compound. [Copyright &y& Elsevier]

Abstract: A novel lithium iron phosphate has been synthesized by a solution route at moderate temperature. The structure was determined from powder by XRD, HRTEM and SAED experiments. LiFe2P3O10 tripolyphosphate crystallizes in the monoclinic system, space group P21 /m, with lattice constants a =4.597(7)Å, b =8.566(4)Å, c =9.051(4)Å, β =97.47° and Z =2. Internal and external vibrational modes (Raman and FTIR) show that the dominant spectral features come from the (P3O10)5− oxo-anions displaying internal and external modes along with the P–O–P bridging modes. Magnetic measurements are consistent with the high-spin configuration of Fe2+ cation with an effective magnetic moment 5.51μB. A weak antiferromagnetic ordering is observed below the Néel temperature at T N =19K. Electron paramagnetic resonance spectroscopy confirms this electronic configuration and provides evidence of the presence of a carbonaceous layer onto the particle surface. Electrochemical measurements were carried out in lithium cells with LiPF6–EC–DEC electrolyte at 25°C. The material delivered a capacity 70mAh/g in the voltage range 2.7–3.9V, close to the theoretical value (72mAh/g). The resulting cyclic voltammogram indicates a stable structure with a good reversibility with the redox peaks at 3.26 and 3.13V vs. Li0/Li+. [Copyright &y& Elsevier]

Abstract: The essential structural features of lithium-metal phosphates (LMP) have been studied using FTIR spectroscopy which is a sensitive tool to probe the local environment in the solid materials. Various LMP materials where M is iron have been investigated including phospho-olivine LiFePO4, diphosphate LiFeP2O7, Nasicon-type phosphate Li3Fe2(PO4)3 and dihydrate FePO4·2H2O. Vitreous and amorphous materials are also considered. Analysis of internal and external modes of vibration allows to distinguish between the different phases and the type of cationic environment in the framework. Results corroborate the contribution of the main factors which are responsible for the complexity of the spectra, i.e. departure from ideal symmetry, interactions between polyhedra, bridging atoms and lattice distortion. [Copyright &y& Elsevier]

Abstract: We report the structural and electronic characterization of Li2FeSiO4 synthesized by solid-state reaction. X-ray diffraction, Raman scattering, Fourier transform infrared (FTIR) spectroscopy, electron paramagnetic resonance (EPR) spectroscopy and magnetization measurements are analyzed. Magnetic susceptibility experiments give evidence that Li2FeSiO4 powders possess an antiferromagnetic ordering below T N =25K due to long range Fe–O–Li–O–Fe interactions. Analysis of the paramagnetic region giving the Curie–Weiss parameters θ p =−93.5K and C p =4.13emuKmol−1 shows the divalent state of Fe cations. Electron paramagnetic resonance experiments confirm this electronic configuration. Electrochemical measurements were carried out in lithium cells with LiTFSI in a poly(ethylene oxide) (PEO) polymer electrolyte at 80°C. The resulting cyclic voltammogram indicates a stable structure for the first cycle with redox peaks at 2.80 and 2.74V versus Li0/Li+. [Copyright &y& Elsevier]