Polymer electrolytes are the subject of intensive study, in part because of their potential use as the electrolyte in all-solid-state rechargeable lithium batteries. These materials are formed by dissolving a salt (for example LiI) in a solid host polymer such as poly(ethylene oxide) (refs 2, 3, 4, 5, 6), and may be prepared as both crystalline and amorphous phases. Conductivity in polymer electrolytes has long been viewed as confined to the amorphous phase above the glass transition temperature, Tg, where polymer chain motion creates a dynamic, disordered environment that plays a critical role in facilitating ion transport. Here we show that, in contrast to this prevailing view, ionic conductivity in the static, ordered environment of the crystalline phase can be greater than that in the equivalent amorphous material above Tg. Moreover, we demonstrate that ion transport in crystalline polymer electrolytes can be dominated by the cations, whereas both ions are generally mobile in the amorphous phase. Restriction of mobility to the lithium cation is advantageous for battery applications. The realization that order can promote ion transport in polymers is interesting in the context of electronically conducting polymers, where crystallinity favours electron transport.

High-yield H-form trititanate nanotubes have been synthesized, and their structures have been characterized by using X-ray diffraction and high-resolution transmission electron microscopy. According to combined TGA/XRD studies, the nanotubes are not stable at high temperature. Thermal analysis suggests that the stoichiometry of the material is H(2)Ti(3)O(7).0.8H(2)O(abs). Conductivity measurements indicate that mainly protonic transport occurs at temperatures below 150 degrees C and that with increasing temperature and progressive breakdown of nanotubes and formation of crystalline TiO(2) phases protonic conductivity is lost, leaving only residual defect electronic conduction. The proton conductivity is ca. 5.5 x 10(-6) S cm(-1) at 300 K. The structural protons and trapped water were confirmed by solid-state NMR.

No abstract

No abstract

AbslmcL Diffusion of lit-based and PFZ-based species in an amorphous p o w e x eleclmlyle has teen explored by pulsed-Beld-gradient (PFG) nuclear magnetic m n a n c e . n e erperiments were undertakn over a range of salt mncentrations and temperature enending 10 lower values of both wriables than in prwious studies Features of the lesults include a demonstration of different mechanisms lor anion and cation lranspon at high concentration, as shown bj their different temperature dependences, a reduced sensitivity of cation diffusion to salt concentration and a failure of the Nemst-Einstein relationship Cation hopping terween ionic dusters and the diffusion of neutral ion pairs are advanced as micmsmpic mechanisms lo aplain the data.