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Blends of PVdF-HFP and ionic liquids (ILs) are interesting for application as electrolytes in plastic Li batteries. They combine the advantages of the gel polymer electrolytes (GPEs) swollen by conventional organic liquid electrolytes with the nonflammability, and high thermal and electrochemical stability of ILs. In this work we prepared and characterized PVdF-HFP composite membranes swollen with a solution of LiTFSI in ether-functionalized pyrrolidinium-imide ionic liquid (PYRA 12O1 TFSI). The membranes were filled in with two different types of silica: (i) mesoporous SiO 2 (SBA-15) and (ii) a commercial nano-size one (HiSil TM T700). The ionic conductivity and the electrochemical properties of the gel electrolytes were studied in terms of the nature of the filler. The thermal and the transport properties of the composite membranes are similar. In particular, room temperature ionic conductivities higher than 0.25 mS cm −1 are easily obtained at defined filler contents. However, the mesoporous filler guarantees higher lithium transference numbers, a more stable electrochemical interface and better cycling performances. Contrary to the HiSil TM-based membrane, the Li/LiFePO 4 cells with PVdF-HFP/PYRA 12O1 TFSI-LiTFSI films containing 10 wt% of SBA-15 show good charge/discharge capacity, columbic efficiency close to unity, and low capacity losses at medium Crates during 180 cycles.

One of the most relevant negative characteristics of high-capacity cathodes for lithium batteries is indeed non-flat voltage-time (V-t) or voltage-capacity (V-C) behaviour during charge-discharge. A clear rationale for this behaviour has not yet been addressed in the literature. Here, by means of density functional theory (DFT) calculations corroborated by basic experimental electrochemical characterization, we investigated both the thermodynamic and the kinetic aspects relevant to voltage variations during charge-discharge of Li 2 FeSiO 4 intended as a model case. A simple physical model allowed us to take into account all the experimental evidence. We suggested that voltage deviations from its theoretical value are due to the formation of undesired delithiated structures caused by concentration gradients. We also related voltage behaviour to relevant quantities such as reaction energies, lithium diffusion coefficients, and particle size, so suggesting some strategies for optimization of materials. Methodology Experimental detailsLi 2 FeSiO 4 /C was synthesized by both nitrate sol-gel and solid state synthesis methods. For the sol-gel method, lithium † Electronic supplementary information (ESI) available: V-C diagrams of discharge measurements of our sample with different rates, and absolute value of slope of charge-discharge diagrams versus square root of the applied rates. See

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We investigate the influence of particle size and crystal orientation on the electrochemical behavior of carboncoated LiFePO 4 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.

Structure, cation distribution, Mn oxidation states, and conductivity behavior of the Mn-substituted (up to 30% of Ti ions) Li 4 Ti 5 O 12 have been investigated by the combined use of X-ray powder diffraction, electron paramagnetic resonance (EPR), 7 Li 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. Mn 2+ ions progressively occupy the tetrahedral site up to an approximately constant value reached for 10% Mn-substituted samples. Mn 3+ ions occupy both octahedral and tetrahedral sites, with a constant value on the tetrahedral one, independent of the total Mn amount; Mn 4+ ions are not detected. The Mn 2+ paramagnetic ions give rise to a through-space interaction with Li + ions of both cationic sites, as evaluated by the area, proportional to the Mn 2+ ions content, of a peak at ∼8 ppm observed in the 7 Li 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 Li 4 Ti 5 O 12 .