Ionic conductivity in glassy PVOH-lithium salt systems

Ionic conductivity (10^-4 S/cm at 25°C) has been observed in glassy poly(vinyl alcohol)/lithium salt complexes. X-ray diffraction patterns indicate that, while the pure polymer is semi-crystalline, the addition of salt suppresses the extent of crystallinity. The glass transition temperatures of these systems are typically in the region of 50-70°C. The conductivity is dependent on the concentration and anion in the lithium salt; LiClO₄ producing the highest conductivities in this work. The presence of unhydrolyzed acetate groups in the polymer backbone causes T_g to be decreased, as compared to the homopolymer, and produces an order of magnitude increase in conductivity. ⁷Li solid state NMR spectroscopy suggests that lithium ion motion is present below T_g indicating that, at least in part, lithium ion motion is responsible for the ionic conductivity and that this motion is decoupled from the polymer segmental motions. ¹⁹F T₁ and T₂ NMR relaxation times were also measured for the anion, and the lack of correlation with the conductivity data suggests anion motion is unlikely to be a major contributor to the conductivity.