Conductivities of some PEO complexes of lithium and sodium salts with aromatic and heterocyclic anions

Abstract

Complexes of poly(ethylene oxide)(PEO) with lithium and sodium salts of benzimidazole, pentafluorophenol and 4-chlorophenol have been prepared with compositions of P(EO)_x, :salt (x= 3, 6 and 10) together with some mixed-salt complexes with excess salt (x= 1 and 2). The complexes with pentafluorophenol salts behave ‘conventionally’ in that the systems with x= 3 form the most crystalline materials and have the lowest conductivities over the range of compositions studied. However, the systems with lithium salts of the other two pseudo acids having x= 3 have high conductivities at temperatures above ca. 60 °C with steeper log σ vs. 1/T plots. It is proposed that in the latter two systems when x= 3, Li⁺ has a specific partially covalent interaction with the anion, giving rise to poorly organised materials. Complexes with mixtures of these two salts have σ > 10^–4 S cm^–1 at 60 °C and > 10^–3 S cm ^–1 at 100 °C. However, a similar interaction is not apparent in pentafluorophenolate salts which induce crystallisation and lower conductivities in mixtures with the others.