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A detailed characterization of the polymorphs constituting cathode materials, both before and after cell cycling, is mandatory to develop more stable and powerful lithium batteries. In many cases, e.g., for transition metal lithium silicates, standard diffraction techniques cannot give a clear-cut response. Here we show that broadband adiabatic fast MAS NMR can give unique information in the case of model Li2(Mn,Fe)SiO4 high-capacity cathode materials. By coupling 7Li and 29Si 1D and 2D spectra, we are able to address polymorphs speciation also in the mixed Mn/Fe compositions, which is a nearly impossible task for X-rays and neutrons diffraction. We finally discuss the conditions under which this approach is useful when applied to rare nuclei such as 29Si.

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