LITHIUM ION MOBILITY IN POLY(VINYL ALCOHOL) BASED POLYMER ELECTROLYTES AS DETERMINED BY LI-7 NMR-SPECTROSCOPY

Solvent-free polymer electrolytes based on poly(vinyl alcohol) (PVA) a nd LiCF3SO3 have shown relatively high conductivities (10(-8)-10(-4) S cm(-1)), with Arrhenius temperature dependence below the differential scanning calorimeter (DSC) glass transition temperature (343 K). This behaviour is in stark contrast to traditional polymer electrolytes in which the conductivity reflects VTF behaviour. Li-7 nuclear magnetic resonance (NMR) spectroscopy has been employed to develop a better und erstanding of the conduction mechanism. Variable temperature NMR has i ndicated that, unlike traditional polymer electrolytes where the linew idth reaches a rigid lattice limit near T-g, the lithium linewidths sh ow an exponential decrease with increasing temperature between 260 and 360 K. The rigid lattice limit appears to be below 260 K. Consequentl y, the mechanism for ion conduction appears to be decoupled from the m ain segmental motions of the PVA. Possible mechanisms include ion hopp ing, proton conduction or ionic motion assisted by secondary polymer r elaxations. (C) 1998 Published by Elsevier Science Ltd. All rights res erved.