Cationic transport in gel electrolytes on basis of oligo(ethylene glycol) dimethacrylate

The cationic part of the charge carrier transport was investigated for gel electrolyte films prepared by photoinitiated polymerization of oligo(ethylene glycol) dimethacrylate (EG)(n)DMA in the presence of a plasticizer and LiCF3SO3. Methyl group terminated oligo(ethylene glycol)s (EG)(n)DME and those with polar endgroups and different n were used to study the influence of the polarity and the chain length of the plasticizer on the cationic transference number. t(+) was determined by the steady state current technique and was calculated from the charge carrier self diffusion coefficients measured by Li-7 and F-19-PFG-NMR with well agreeing results. Endcapping of plasticizers by polar groups enhances t(+) due to an improved charge carrier separation which is discussed as deviation from the Nernst-Einstein equation. In gel electrolytes t(+) was found to depend on the ability of the plasticizer to coordinate cations in competition with the polymer. Therefore, relatively high t(+) values (t(+) > 0.3) were observed for gel electrolytes containing higher molecular oligo(ethylene glycol)s as plasticizer or a reduced content of ethylene glycol units in the polymer network. The interactions between charge carriers and plasticizers in the liquid electrolyte systems have been characterized by the Stokes' radii of the plasticizer and the charge carriers. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.