Electrical, thermal and NMR investigation of composite solid electrolytes based on PEO, LiI and high surface area inorganic oxides

High salt concentration polymer composite electrolytes, containing poly(ethylene oxide) (PEO), LII and nanoscale Al2O3 Or MgO and, in some cases, ethylene carbonate (EC) and poly(methyl methacrylate) (PMMA), were investigate by electrical conductivity, differential scanning calorimetry (DSC) and both wide-line and high resolution solid state Li-7 NMR. The high resolution NMR spectrum of a sample with a PEO:Li ratio of 3:2 is consistent with at least two Li environments, one solvated by the polymer and one in small ionic clusters. A correlation between the observed change in Li environment at elevated temperature and a sudden increase in conductivity is suggested. All results demonstrate that the conduction mechanism in concentrated composite electrolytes is; significantly different than in more dilute polymer electrolytes, in which the ion transport process is associated with polymer segmental motion. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.