The molar conductivity behavior in polymer electrolytes at low salt concentrations : a raman study of poly(propylene glycol) complexed with LiCF3SO3

• Raman scattering measurements have been carried out on poly(propylene glycol) complexed with LiCF3SO3 salt over a wide salt concentration range, the ether oxygen to alkali metal cation ratios (O:M) ranging from 4820:1 to 12:1. The relative concentrations of solvated anions, anion-cation pairs and ionic aggregates have been calculated from an analysis of the symmetric anion stretch. The degree of association is found to be almost constant in the O:M range 4820:1-40:1 whereafter it increases with increasing salt concentration. The results show that the dramatic increase reported for the molar conductivity in the O:M range 1000:1-40:1 cannot be explained by the redissociation of contact ion pairs or the formation of conducting triplets. Instead the major contribution to the conductivity increase seems to be a concentration dependent enhancement of the ionic mobility. A percolation based ionic hopping process involving exchange between ions in pairs and dissolved ions, either free or coordinated to ether oxygen sites, is advanced as a possible microscopic mechanism.

Subject headings

NATURVETENSKAP  -- Fysik -- Den kondenserade materiens fysik (hsv//swe)

NATURAL SCIENCES  -- Physical Sciences -- Condensed Matter Physics (hsv//eng)

Keyword

Raman scattering

conductivity

polymer electrolytes

poly(propylene glycol)

LiCF3SO3

ion association

ionic mobility

hopping

diffusion

Publication and Content Type

ref (subject category)

art (subject category)