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Transition metal-based lithium orthosilicates (Li2MSiO4,M=Fe, Ni, Co, Mn) are gaining a wide interest as cathode materials for lithium-ion batteries. These materials present a very complex polymorphism that could affect their physical properties. In this work, we synthesized the Li2FeSiO4 and Li2MnSiO4 compounds by a sol-gel method at different temperatures. The samples were investigated by XRPD, TEM, 7Li MAS NMR, and magnetization measurements, in order to characterize the relationships between crystal structure and magnetic properties. High-quality 7Li MAS NMR spectra were used to determine the silicate structure, which can otherwise be hard to study due to possible mixtures of different polymorphs. The magnetization study revealed that the Neel temperature does not depend on the polymorph structure for both iron and manganese lithium orthosilicates

Li2MSiO4 (M = Fe, Mn, etc.) are promising cathode materials for Li-ion batteries. One appealing strategy for improving their cathode properties is to develop mixed transition metal compounds. Density Functional Theory calculations were performed to evaluate the structural, magnetic and electrochemical properties of Li2M0.5N0.5SiO4 compounds. Our theoretical study allows us to individuate the most promising candidates for practical applications in lithium batteries

Transition metal lithium orthosilicates are promising cathode materials for lithium-ion batteries. Here we report a combined experimental (in situ X-ray diffraction) and computational (static lattice and molecular dynamics) study of the thermal behavior of the Li2Fe0.5Mn0.5SiO4 orthosilicate from room temperature to 950°C. Our X-ray results showed that Pmnb polymorph is the most stable all over the explored temperature range. A significant cation disorder up to 80%, based on the anti-site defect, was found. The defect concentration depends on the synthesis route and temperature, and is completely reversible after the thermal treatments. Moreover, a careful analysis of the impurity phases allowed us to identify Li2SiO3, Fe3O4 and Li3Fe5O8, the last one never reported before.The minimization of defects by opportunely tuning the synthetic parameters would be of great importance in view of potential applications of these materials in lithium batteries

The global energy demand calls for more efficient storage systems. In this review, the state of the art of Li/air and Li/O 2 batteries is discussed with particular attention on the more recent findings regarding all the battery compartments. Both aqueous and non-aqueous systems are considered, and the most critical issues for better battery design are addressed. Whereas the predicted charge/discharge values for these devices do justify the intense research efforts performed nowadays, great problems are still present which must be overcome in order to make Li/air and Li/O 2 a reality for future large-scale applications

Olivine-type LiFePO 4 is nowadays one of the most important cathode materials of choice for high-energy lithium ion batteries. Its intrinsic defectivity, and chiefly the so-called lithium iron anti-site, is one of the most critical issues when envisaging electrochemical applications. This paper reports a combined diffractometric (Synchrotron Radiation XRD with Rietveld and PDF analyses) and spectroscopic (Mössbauer) approach able to give a thorough characterization of the material defectivity. Such analytical procedure has been applied to a sample prepared following an innovative microwave-assisted hydrothermal synthesis route that, in a few minutes, allowed us to obtain a well crystallized material. PDF analysis, which is applied for the first time to this type of battery material, reveals the presence of disorder possibly due to Li/Fe exchange or to a local symmetry lowering. A 5% amount of iron on the lithium site has been detected both by PDF as well as by Mössbauer spectroscopy, which revealed a small percentage of Fe 3+ on the regular sites

The study of the ionic conducting material LiTi2(PO 4)3 and of its Mn-substituted derivate reveals that the Mn distribution is strictly related to the synthetic method. The results of the structural refinement of X-ray and neutron (ToF) powder diffraction data and of XPS analysis demonstrate that Mn2+ ions are located on the lithium octahedral site, while Mn3+ and Mn4+ ions occupy the titanium ones. The Mn2+ amount on the lithium site seems to be the main factor responsible for the conductivity decrease observed in doped samples. The EPR spectra evidence clustering effects of Mn on both Li and Ti sites and the presence of more insulated Mn2+ ions. The effect of the major Mn amount on Ti site in the case of the sol-gel synthesis is consistent with the different EPR line shape of the related sample. The neutron diffraction and 7Li MAS NMR results do reveal that lithium occupies the M1 site of the rhombohedral LiTi2(PO4)3 structure.

We investigate the influence of particle size and crystal orientation on the electrochemical behavior of carbon-coated LiFePO4 prepared by a hydrothermal synthesis in the presence of a polymeric surfactant and a source of carbon. We evaluated the charge/discharge profiles of two samples, one constituted by particles in the micrometer range with a platelet-like shape (large ac facet and (020) crystal orientation) and another made of sub-micrometer-rounded particles with a random crystal orientation. At low current rates the crystal orientation seems to be the prevailing factor, whereas at high current rates smaller particles can allow a shorter electronic conduction path, so reducing the resistance experienced by Li ions during diffusion

Cr- and Ni-doped Li4Ti5O12 compound has been characterized through the combined use of X-ray powder diffraction, electron paramagnetic resonance (EPR), 7Li nuclear magnetic resonance magic-angle spinning (NMR-MAS), micro-Raman, and magnetization measurements. The doping, occurring on the octahedral site of the cubic Li4Ti5O12 spinel lattice, strongly affects both the local and the average structural properties. The glassy character of the observed EPR signals suggests structural disorder in the stable Li4Ti5O12 matrix and the presence of clustering phenomena or nonhomogeneous distribution of the dopant ion, as also supported by 7Li NMR-MAS, micro-Raman, and magnetization results. The computation by numerical method of the complex EPR signal of the Cr-doped sample suggests that both CrTi and CrLi substitutions occur, giving rise to two distinct EPR components, corresponding to opposite axial distortion of the relative octahedral environments. On the basis of the compositional data, defect models involving oxygen or cation vacancies are proposed to explain the conductivity of the doped material

Bioactive glasses and glass-ceramics of the system SiO2-P2O5-CaO with and without zinc were synthesized by sol-gel with the aim to address the influence of both the chemical composition and the microstructure on the growth of hydroxycarbonate apatite (HCA) following soaking in simulated body fluid (SBF). In the standard compositions 58S, 70S, and 80S the silica precursor was also partially replaced with a nanoscale silica powder (HiSil) in order to separate the contributions of porosity and composition. The combined use of XRPD, N2 absorption measurements, and SEM allowed us to establish quantitative correlations among the above-mentioned quantities. We found that the HCA formation rate increases with the silica content and that an important role is played by the specific surface area of the samples. Notably, the addition of even small quantities (0.4 wt%) of ZnO at the expenses of both CaO and P2O5 in the 58S glass leads to the increase, with respect to the 58S sample, of both the HCA formation rate and the HCA content after 8 days of treatment in SBF. A preliminary result revealed that sample with 0.4 wt % ZnO displayed good in vitro biocompatibility as shown by LDH assay

Structure, cation distribution, Mn oxidation states, and conductivity behavior of the Mn-substituted (up to 30% of Ti ions) Li4Ti5O12 have been investigated by the combined use of X-ray powder diffraction, electron paramagnetic resonance (EPR), 7Li MAS NMR, and impedance spectroscopy techniques. The spinel structure of the lithium titanate is preserved and the lattice parameter decreases with increasing the Mn content. Mn2+ ions progressively occupy the tetrahedral site up to an approximately constant value reached for 10% Mn-substituted samples. Mn3+ ions occupy both octahedral and tetrahedral sites, with a constant value on the tetrahedral one, independent of the total Mn amount; Mn4+ ions are not detected. The Mn2+ paramagnetic ions give rise to a through-space interaction with Li+ ions of both cationic sites, as evaluated by the area, proportional to the Mn2+ ions content, of a peak at ∼8 ppm observed in the 7Li NMR spectra for the substituted samples. The obtained cation distribution and the Mn valence states satisfactorily explain the decrease of conductivity observed in the Mn-doped samples with respect to the pure Li4Ti5O12

The room temperature cation occupancy in LiMgVO4 and LiZnVO4 crystallographic sites is obtained by means of the combined use of X-ray powder diffraction (XRPD), Li-7 and V-51 magic angle spinning nuclear magnetic resonance (MAS NMR), and micro-Raman measurements. In the LiMgVO4 Cmcm orthorhombic structure, the 4c (C-2v symmetry) tetrahedral vanadium site is fully ordered; on the contrary, the Li 4c tetrahedral site and the 4b (C-2h symmetry) Mg octahedral site display about 22% of reciprocal cationic exchange. Higher cationic disorder is observed in LiZnVO4: the three cations can distribute on the three tetrahedral and distinct sites of the R-3 structure. XRPD and MAS NMR analysis results highly agree for what concerns vanadium ion distribution on the three cationic sites (about 25, 26, and 47%). From the full profile fitting of XRPD patterns with the Rietveld method, it is also obtained that Li+ displays a slightly preferred occupation of the T1 position (similar to 55%) and Zn2+ of the T2 position (similar to 46%). The vibrational spectra of the two compounds are characterized by different peak positions and broadening of the Raman modes, reflecting the cation distribution and the local vibrational unit distortion. A comparison is also made with recent Raman results on Li3VO4. High temperature XRPD measurements rule out possible structural transitions up to 673 K for both compounds

The structural evolution of LiMn2O4 spinel was followed from 320 K down to 10 K. The structural transformation, recently studied down to 230 K [Rodriguez-Carvajal, Rousse, Masquelier & Hervieu (1998). Phys. Rev. Lett. 81, 4660-4663], takes place near room, Addresses: Massarotti V, Univ Pavia, Dipartimento Chim Fis, Viale Taramelli 16, I-27100 Pavia, Italy. Univ Pavia, Dipartimento Chim Fis, I-27100 Pavia, Italy. Univ Pavia, CNR, CSTE, I-27100 Pavia, Italy. Univ Trent, Dipartimento Ingn Mat, I-38050 Trent, I

Lithium manganese spinel Li1+yMn2-yO4 (0.0 less than or equal to y less than or equal to 0.07) synthesized by the sol-gel process is studied with a focus on the effects of the changes of formation conditions which can sensibly determine the mean crystallite size from a few nanometers to several hundred nanometers. Changes of stoichiometry and abundance of the spinel phase can be observed in the 573 less than or equal to T-A (K) less than or equal to 1073 range of annealing temperature (T-A). Comparing spinel phases obtained by sol-gel and solid state synthesis evidences the correlation among composition, structure, and electric and magnetic properties. (C) 1999 Academic Press.

The electrical conductivity of lithium-manganese spinels is analyzed in samples with different starting Li cationic fraction x. Li-rich spinels, resulting from Li-Mn substitution around the stoichiometric value (x = 0.333), show conductivity values higher than that observed in stoichiometric LiMn2O4. Besides, a conductivity drop, associated with a structural phase transition at about 290 K in LiMn2O4, progressively disappears by decreasing x, while it is absent in Li-rich samples. Stoichiometry effects on the concentration of charge carriers and on the available sites for the hopping transport process are evaluated, as well as the effects due to coexisting insulating phases. The role of the Jahn-Teller effect on the conductivity behaviour of stoichiometric and Li-poor spinels is also considered.

The Raman spectrum of the metastable Mn5O8 phase, obtained from slow oxidation of Mn3O4 at low temperature, is presented and analysed for the first time and the thermal stability is monitored by the changes in Raman spectra due to laser-induced thermal treatments. A structural transformation toward the spinel phase Mn3O4 is observed at temperature higher than 1000 K. Other Mn oxides, characterised by intermediate Mn oxidation states, are not detected below or during the transition. A compositional model of the sample grains is also proposed by comparing Raman data with X-ray diffraction and scanning electron microscopy measurements. (C) 1999 Elsevier Science Ltd. All rights reserved.

The present paper details the way to determine the cation distribution in mixed oxides with transition ions from the diffraction and magnetic susceptibility data. This approach allows one to determine phase abundances and phase compositions by two combined procedures. By X-ray diffraction Rietveld profile refinement and magnetic susceptibility data analysis it is possible to estimate the ratio and the occupancy factor of paramagnetic ions in different oxidation states. A brief discussion of practical cases is reported. In the Li-Ni-O system the lithium cationic fraction of the ordered phase Li2xNi2-2xO2 increases monotonically with the total lithium fraction x1 for 0.31 ≤ x1 ≤ 0.46. In the Li-Mn-O system for 0.36 ≤ x1 ≤ 0.53 the Li2MnO3 fraction has been determined, and for the coexistent Li [LiyMn2-y]O4 spinel phase the dependence of y on x1 has been evaluated.

Magnetic measurements were carried out on different samples of Lithium-Manganese spinel LiMn2O4, great care having been taken to avoid the presence of spurious magnetic phases, such as Mn3O4. Susceptibility data, showing deviations from paramagnetic behaviour at about 40 K, were analyzed in terms of local magnetic interactions, taking into account the structural and transport properties of these compounds. The magnetic response of pure and stoichiometric samples suggests that the onset of a long-range magnetic ordering is hindered by the topological frustration of the antiferromagnetic octahedral sublattice of the spinel.

X-ray diffraction (XRD) and (Formula presented) measurements have been performed on (Formula presented)(Formula presented) (lithium cationic fraction, x=0.333), (Formula presented)(Formula presented) (x=0.667), and the intermediate composition with x=0.40. The use of magic angle spinning produces complex manifolds of the spinning sidebands. The predominant interaction affecting the NMR spectrum is the transferred hyperfine coupling (TFHI) between the Mn ions and the Li spins. TFHI parameters are extracted from MAS-NMR spectra of oxides containing a large quantity of manganese. We obtained a full spectral assignment for the spinel (Formula presented)(Formula presented), for the rocksalt (Formula presented)(Formula presented), and for the x=0.40 sample, which contains the rocksalt and both stoichiometric and nonstoichiometric spinel phases. According to XRD data, the rocksalt phase contains three nonequivalent lithium sites whose NMR peaks are shifted upfield from x=0.667 to 0.40 because of the cell volume expansion.mThe (Formula presented) ions belonging to the two spinel phases of x=0.40 are quite mobile and give origin by motional narrowing to a single peak, which is slightly shifted upfield with respect to that of (Formula presented)(Formula presented).

XRD measurements proved the coexistence of spinel, lithium-rich spinel, and rock-salt phases in the Li-Mn-O system. An investigation of the electrical properties, carried out on polycrystalline samples, shows that Li2MnO3 has insulating behavior while the spinel phases provide an example of hopping conduction mechanism. The negative Seebeck coefficient suggests that electrons constitute the charge carriers and their number is consistent with the fraction of Mn3+ over the total number of Mn3+ and Mn4+ sites in the spinel structure. The static magnetic susceptibility results agree with the presence of the Mn3+ ions in high spin configuration. (C) 1997 Academic Press.