In Li-ion batteries, Li 4 Ti 5 O 12 (LTO) has merits of an excellent cycling stability combined with a safe working potential of 1.55 V vs. Li + /Li at which no adverse side-reactions with the electrolyte are expected. Concerns regarding gassing of LTO, especially at elevated temperatures, have however recently been reported. In this work, LTO gassing behavior at 50 • C is investigated by in situ pressure and online electrochemical mass spectrometry (OEMS), allowing for both qualitative and quantitative analysis of evolving gases. H 2 , C 2 H 4 , and CO 2 are the dominantly evolving gases for ethylene carbonate (EC) based electrolytes. H 2 is mainly produced during the first charge step, while C 2 H 4 is observed at lower potentials resulting from the reduction of EC. CO 2 evolution mechanism is complex and is promoted at more anodic potentials. Passivating the LTO surface, e.g. by a proper coating, and/or exchanging the LiPF 6 salt, may effectively reduce gas evolution, thus clearing the way for future use of LTO in energy storage applications at elevated temperatures.

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The structure of Li 4 Ti 5 O 12 was investigated by neutron powder diffraction, and the study revealed unprecedented details about lithium migration at high temperatures. A commercial sample of the battery anode material Li 4 Ti 5 O 12 (spinel-type) was measured from room temperature to 1100 °C. Up to 500 °C, linearly increasing values for the unit cell parameter, the isotropic atomic displacement parameters, and the oxygen position are observed. At 700 °C, a change of slope occurs, which is assigned to the beginning migration of lithium. Previous investigations identified the octahedral 16c site in the spinel structure as the migration position of lithium upon heating to high temperatures, and because of that, several phase transitions of Li 4 Ti 5 O 12 at high temperatures have been proposed. Here, we unambiguously identify that the lithium atoms occupy split sites around the 16c positions and orderÀdisorder phase transitions of Li 4 Ti 5 O 12 were not observed. One-particle potential shows that the occupancy of 16c is an unstable configuration and that the split-site structure leads to a more favorable migration position. Occupation of the lithium sites (32e) results in the same long-range diffusion path in all AE110ae directions. The onset of lithium migration can explain the change of the ionic conductivity of Li 4 Ti 5 O 12 at high temperatures, which has been observed by impedance spectroscopic studies. Further heating to 1000 °C resulted in a partial decomposition of Li 4 Ti 5 O 12 into the ramsdellite-type Li 2 Ti 3 O 7 and the cubic γ-Li 2 TiO 3 , and at 1100 °C, the Li 4 Ti 5 O 12 spinel was fully decomposed.

International audienceTuff has been extensively used as a building material in volcanically and tectonically active areas over many centuries, despite its inherent low strength. A common and unfortunate secondary hazard accompanying both major volcanic eruptions and tectonic earthquakes is the initiation of catastrophic fires. Here, we report new experimental results on the influence of high temperatures on the strength of three tuffs that are commonly used for building in the Neapolitan region of Italy. Our results show that a reduction in strength was only observed for one tuff, the other two were unaffected by high temperatures. The cause of this strength discrepancy was found to be a product of the initial mineralogical composition, or, more specifically, the presence of thermally-unstable zeolites within the initial rock matrix. The implications of these data are that, in the event of fire, only the stability of buildings or structures built from tuff containing thermally-unstable zeolites will suffer. Unfortunately, this includes the most widespread dimension stone in Neapolitan architecture. We recommend that this knowledge should be considered during fire hazard mitigation in the Neapolitan area and that other tuffs used in construction worldwide should be tested in a similar way to assess their fire resistance

Li 4 Ti 5 O 12 , which is a high performance anode material for rechargeable Li-ion batteries, is crystallized directly via a novel continuous flow hydrothermal method using lithium ethoxide and titanium isopropoxide as reactants. Crystalline nanoparticles are obtained in a single step and in less than one minute, by mixing the reactants with superheated water in a continuous flow reactor at nearand supercritical conditions. The Li 4 Ti 5 O 12 nanoparticles have an average crystallite size of 4.5 nm with a specific surface area of ≥230 m 2 /g. In-situ synchrotron powder X-ray diffraction measurements upon annealing of the nanocrystalline Li 4 Ti 5 O 12 were performed in order to investigate the structural and microstructural changes from room temperature to 727 • C. The as-prepared crystalline nanoparticles show significant crystallographic strain, which is found to relax upon annealing above 500 • C, concurrent with crystallite growth. Electrochemical tests of the as-prepared Li 4 Ti 5 O 12 and a sample annealed at 600 • C reveal that heat-treatment results in a significant improvement of the performance in terms of the specific capacity and the rate capability, and overall the annealed nanoparticles have excellent electrochemical properties. The origin of the crystallographic strain is discussed, and further optimization of this rapid, green and scalable synthesis approach is suggested.