For the development of safe and long-lasting lithium-ion batteries we need electrolytes with excellent ionic transport properties. Argyrodite-type Li 6 PS 5 X (X: Cl, Br, I) belongs to a family of such a class of materials offering ionic conductivities, at least if Li 6 PS 5 Br and Li 6 PS 5 Cl are considered, in the mS cm À1 range at room temperature. Although already tested as ceramic electrolytes in battery cells, a comprehensive picture about the ion dynamics is still missing. While Li 6 PS 5 Br and Li 6 PS 5 Cl show an exceptionally high Li ion conductivity, that of Li 6 PS 5 I with its polarizable I anions is by some orders of magnitude lower. This astonishing effect has not been satisfactorily understood so far. Studying the ion dynamics over a broad time and length scale is expected to help shed light on this aspect. Here, we used broadband impedance spectroscopy and 7 Li NMR relaxation measurements and show that very fast local Li ion exchange processes are taking place in all three compounds. Most importantly, the diffusion-induced NMR spinlattice relaxation in Li 6 PS 5 I is almost identical to that of its relatives. Considering the substitutional disorder effects in Li 6 PS 5 X (X = Br, Cl), we conclude that in structurally ordered Li 6 PS 5 I the important inter-cage jump processes are switched off, hindering the ions from taking part in long-range ion transport. † Electronic supplementary information (ESI) available: Rietveld refinements and structural data, further NMR data. See Li 6 PS 5 I are also included. The lower part of the graph shows s DC T(1/T); the values given represent activation energies. For the sake of clarity, data of Li 6 PS 5 Br 0.75 I 0.25 (solid line, grey) have been plotted using an offset of +1 on the log scale.Li 6 PS 5 Cl 0.11(1) 0.18(2) 0.17(4) Li 6 PS 5 Br 0.06(1) 0.09(1) 0.10(4) Li 6 PS 5 I 0.23(1) 0.38(2) 0.18 (5) Paper PCCP

Lithium titanate (LTO) is one of the most promising anode materials for large-scale stationary electrochemical storage of energy produced from renewable sources. Besides many other aspects, such as negligible formation of passivation layers and no volume expansion during lithiation, the success of LTO is mainly based on its ability to easily accommodate and release Li ions in a fully reversible way. This feature is tightly connected with Li self-diffusion. As yet, little information is available about microscopic Li diffusion properties and elementary steps of Li hopping at low intercalation levels, i.e., at values of x being significantly smaller than 1. Here, we used 7Li spin-locking NMR relaxometry to probe absolute hopping rates of LTO (homogeneous) solid solutions in quasi-thermodynamic equilibrium. As a result, the largest increase of Li diffusivity is observed when small amounts of Li are inserted. Strong Coulomb repulsions caused by the simultaneous occupation of neighboring 8a and 16c sites serve as an explanation for the enhanced Li diffusivity found. At even larger values of x, Li mobility slows down but is still much faster than in the host material with x = 0. Our results experimentally corroborate the outcome of recently published calculations on the DFT level focusing on both dynamic and structural aspects. The findings favor the formation of LTO solid solutions upon chemical lithiation; the steep increase in Li diffusivity found might also help with understanding the flat insertion potential observed.

The electrochemical and thermal performances of commercial LiCoO 2 as cathode material of lithium-ion batteries were improved by soaking the nano-Al 2 O 3 in commercial LiPF 6 /ethylene carbonate/dimethyl carbonate electrolyte. The acidity of the new electrolyte is much higher than that of the original ͑commercial͒ electrolyte. These observations cannot be explained with traditional models of performance improvement by surface coating/modification. A solid superacid model was proposed based on extended and comprehensive analyses. This model disagrees with previous improvement mechanisms and predicts that some other nanocompounds can also be used as additives for improving the performances of LiCoO 2 cathode materials.

The long-term performance of commercial lithium-ion batteries used in today's electric vehicles is of utmost importance for automotive requirements. Here, we use Tesla's 18650 cells manufactured by Panasonic to elucidate the origins of capacity fading and impedance increase during both calendar and cycle aging. Full cell testing is systematically carried out at three different temperatures (25 • C, 40 • C, 60 • C). The cells are galvanostatically cycled at different C-rates (0.33 C -1 C) and calendar aging is monitored at 4 different state-of-charges (SOC). Operation at high temperatures turns out to have the largest effect on both the capacity and direct current (DC) impedance. As an example, after 500 cycles at 25 • C and 40 • C capacity fading is approximately 12%, while at 60 • C the fading reaches 22%. Our DC impedance measurements reveal the same trend. Post mortem analysis indicate that aging is strongly related to changes of the solid electrolyte interphase (SEI). Hence, the changes in performance are correlated with the change in composition (and thickness) of the SEI formed. In particular, we quantitatively measure the formation of electrically insulating LiF and find a correlation between overall DC impedance of the cells and lithium fluoride of the SEI. For years to come, Li-ion batteries are considered as one of the most attractive energy storage devices for electric vehicles. They benefit from a high specific energy density combined with a good cycle life. In order to further enhance conventional lithium-ion technology it is necessary to develop new materials and to improve existing battery concepts including, e.g., also the ways how cells are fabricated on an industrial scale. In particular, the latter includes aging studies on commercially available batteries. Such studies are essential for predicting the practical lifetime of the batteries and for assisting in identifying the main failure mechanisms that may, for example, involve lithium plating, passivating surface films properties, co-intercalation, dissolution or electrochemical re-plating of metal ions.In particular, for automotive applications, where long cycle and calendar life is indispensable, accurate knowledge about the origins of battery aging is a major point of interest since it helps predict the operational lifetime of the systems. Understanding and identifying the main failure mechanisms, induced by certain operating conditions, would be a significant step forward in terms of reliability and lifetime costs of electric vehicles. Due to the fact that battery aging is a very complex matter, which is sensitively influenced by many factors such as temperature, storage and operating conditions as well as the types of active materials or electrolytes used, the variety of studies that focused on different aging phenomena is immense. Studies range from detailed material and component tests, e.g., on electrolytes, anodes and cathodes used, to investigations on fully commercial systems. As early as 1979 Peled 1,2 introduced the idea of the f...

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