New batteries are needed urgently to meet the demands of modern technology and to address the challenge of global warming.[1] Rechargeable lithium-ion batteries (graphite anode/liquid electrolyte/LiCoO 2 cathode) have a higher energy density and lower toxicity than conventional lead-acid, nickel-cadmium, and even nickel-metal hydride batteries; as a result they have revolutionized consumer electronics.[2] However, they suffer from high cost, low power, and intrinsic safety concerns that necessitate careful electronic control of the cell. The key to overcoming these problems, essential if lithium-ion batteries are to be used for applications such as hybrid electric vehicles, lies in new electrode and electrolyte materials, especially new nanostructured materials, which can improve the rate of intercalation/deintecalation and hence the power density of the battery. [3] There has been much interest TiO 2 (B) nanowires may be synthesized in high yield and relatively high quantities by a simple hydrothermal reaction between NaOH and TiO 2 anatase as described previously (see Experimental section).[6] Transmission electron microscopy carried out on the TiO 2 (B) nanowires revealed that they have diameters confined to a narrow distribution in the range 20 to 40 nm and may be up to several micrometers long. The surface area of the material used here was 36 m 2 g -1 . The crystal structure of the nanowires was shown to be that of TiO 2 (B) by powder X-ray diffraction and detailed high-resolution electron microscopy.[6] Like rutile, anatase, and brookite the structure consists of edge-and corner-sharing TiO 6 octahedra; however, in this case they are arranged to form perovskitelike pathways along which inserted lithium ions may undergo facile transport. The density (3.73 g cm -3 ) is somewhat less than the other polymorphs (rutile 4.25 g cm -3 , anatase 3.89 g cm -3 , brookite 4.13 g cm -3 ), which also aids lithium-ion diffusion.The gel-polymer electrolyte (GPE), formed by trapping a LiPF 6 -EC-PC (EC: ethylene carbonate; PC: propylene carbonate) solution in a poly(vinlydene fluoride) (PVdF) polymer matrix, being a solid-liquid hybrid, has mechanical properties similar to solid polymers and an electrochemical stability exceeding that of the pure liquids, as a result of interactions between the liquid phase and the polymer matrix. Indeed, the electrochemical stability window extends from 0.9 V to 5.0 V versus lithium.[4f] The conductivity of the gels is comparable to that of the parent liquid. [4f,7] The insertion/removal of lithium in TiO 2 (B) occurs at a potential around 1.5 V versus lithium.[5] The corresponding process for LiFePO 4 is associated with a potential of approximately 3.5 V versus lithium.[8] Thus, the TiO 2 anode-LiFePO 4 cathode combination gives a battery in which lithium ions are cycled between the two electrodes with an operating voltage approaching 2 V. The results of cycling a TiO 2 (B)-GPE-LiFePO 4 battery (constructed as described in the methods section) are presented in Figure 1a, which shows t...

Lithium-ion batteries are light and compact and operate using voltages on the order of 4 V and with energy densities ranging between 150 W h kg À1 and 250 W h kg À1

Conversion reactions in lithium batteries have been proved for several classes of materials, such as oxides, fluorides, sulphides, nitrides, phosphides and recently for hydrides. Metal hydrides can be electrochemically reduced to a highly conductive composite material consisting of nanometric metallic particles dispersed in an amorphous LiH matrix. Magnesium hydride undergoes a reversible conversion reaction and it has very good theoretical performances, i.e. a theoretical specific capacity of 2038 mA h g -1 and a working potential of 0.5 V vs. Li +/Li. The purpose of our study is to investigate the MgH 2 redox activity by evaluating the effect of ball milling pre-treatments and by studying the conversion reaction mechanism. Three materials, prepared by submitting bulk MgH 2 to different ball milling procedures, are investigated. By coupling electrochemical tests, ex situ X-ray powder diffraction and transmission electron microscopy, we prove that the lithium incorporation does not follow a simple direct conversion path as it follows at least a sequence of four consecutive processes: (a) the hydride conversion reaction of MgH 2 to give Mg and LiH, (b) the alloying of Li in hcp Mg and (c and d) the formation and lithium enrichment of a bcc Li-Mg solid solution. Furthermore some experimental clues suggest that the mechanism is probably even more complex as it can imply the formation of other unknown intermediate Li-Mg-H phases. Moreover large morphological changes occur upon lithium incorporation in the electrodes: in particular an extended sintering of the metal nanoparticles occurs upon cycling. This effect leads to electrode pulverization and capacity fading. On the other hand MgH 2 shows a very limited potential hysteresis between discharge and charge and very promising kinetics at high current. © 2012 The Royal Society of Chemistry

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.

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