Effect of pressure on ion transport in amorphous and semi-crystalline polymer electrolytes

Abstract

Ionic conductivities of polyethylene oxide (PEO) complexes with LiClO₄ have been measured at pressures up to 200 MPa over the temperature range 303–353 K. Two systems differing in phase morphology are compared by reference to their temperature-dependent activation energies and volumes. For an amorphous complex of composition PEO ∶ LiClO₄(6 ∶ 1), Vogel–Tammann–Fulcher (VTF) behaviour is found, enabling activation energies to be calculated as a function of temperature from the best fit equation, while activation volumes are obtained directly from the isothermal pressure dependence of the conductivity. While the behaviour of the amorphous complex is adequately described by the free volume model, the corresponding data for a polycrystalline material of overall 20 ∶ 1 stoichiometry suggests the prevalence of surface conduction at lower temperatures. Such variable-pressure, variable-temperature (VPVT) data may in future provide new insights into the behaviour of more complex polymer electrolyte systems.