The physical and chemical properties of a new class of lithium conducting polymer electrolytes formed by dispersing ceramic powders at the nanoscale particle size into a poly(ethylenoxide) (PEO)-lithium salt, LiX complexes, are reported and discussed. These true solid-state PEO-LiX nanocomposite polymer electrolytes have in the 30-80 °C range an excellent mechanical stability (due to the network of the ceramic fillers into the polymer bulk) and high ionic conductivity (promoted by the high surface area of the dispersed fillers). These important and unique properties are accompanied by a wide electrochemical stability and by a good compatibility with the lithium electrode (assured by the absence of any liquids and by the interfacial stabilizing action of the dispersed filler), all this making these nanocomposite electrolytes of definite interest for the development of advanced rechargeable lithium batteries.

No abstract

In-situ X-ray diffraction studies have been performed on a Li 4/3 Ti 5/3 O 4 electrode upon cycling in a Li cell, by using a very high energy (87.5 keV) synchrotron beam. The real time structural changes of its crystalline lattice were observed over two complete cycles of the cell. The high-resolution measurements allowed us to precisely monitor the extremely small breathing movement of the structure and to plot the curve of the lattice parameter as a function of the lithiation degree. The investigation revealed an unexpected behavior in the structural evolution upon cycling, which was attributed to the reversible passage from a monophasic to a biphasic domain upon insertion. Furthermore, the structural evolution turned out to be slightly different in the first and in the second cycle. This suggests that irreversible rearrangements, like the ones observed for every other insertion compound, occur also in this case, although on an extremely smaller scale.

Upon submonolayer deposition of silicon onto the anisotropic silver (110) surface flat lying individual Si nanowires, all oriented along the [−110] direction, can be grown at room temperature with a high aspect ratio. Upon deposition at ∼200°C, these one-dimensional nanostructures self-assemble by lateral compaction to form a regular array of essentially identical nanowires, ∼1.6nm in width, covering uniformly the entire substrate surface. They realize, at macroscopic sizes, a highly perfect one-dimensional grating with a molecular-scale pitch of just 2nm.

Several types of lithium ion conducting polymer electrolytes have been synthesized by hot-pressing homogeneous mixtures of the components, namely, poly(ethylene oxide) (PEO) as the polymer matrix, lithium trifluoromethane su.lfonate (LiCF3SO3), and lithium tetrafluoborate (LiBF4), respectively, as the lithium salt, and lithium gamma-aluminate -y-LiA1O2, as a ceramic filler. This preparation procedure avoids any step including liquids so that plasticizer-free, composite polymer electrolytes can be obtained. These electrolyte have enhanced electrochemical properties, such as an ionic conductivity of the order of i0 S cm' at 80-90°C and an anodic breakdown voltage higher than 4 V vs. Li. In addition, and most importantly, the combination of the dry feature of the synthesis procedure with the dispersion of the ceramic powder, concurs to provide these composite electrolytes with an exceptionally high stability with the lithium metal electrode. In fact, this electrode cycles in these dry polymer electrolytes with a very high efficiency, i.e., approaching 99%. This in turn suggests the suitability of the electrolytes for the fabrication of improved rechargeable lithium polymer batteries.