Conductivity relaxation in the PEO-salt polymer electrolytes

The ionic conductivity of polyethylene oxide (PEO)-based electrolytes is complicated due to the coexistence of crystalline and amorphous phase below melting point of PEO complexes. The two-phase characteristics are greatly dependent upon thermal history, exhibiting variety of spherulitic morphology and crystallinity. Further complicacy comes from slow crystallization kinetics of the spherulites. We found that the ionic conductivity of PEOnLiClO4 polymer electrolytes under isothermal conditions, after quenching from high-temperature phase, drops significantly for roughly first 10 h and then decreases very slowly thereafter. The conductivity relaxation observed can be assigned to be a consequence of the slow recrystallization kinetics of PEO. It corresponds to a gradual, slow secondary crystallization of PEO and PEO-salt complexes corresponding to thickening of spherulitic aggregates, possibly through a development of subsidiary lamellae which fill in the space between the dominant lamellae crystals. Hence, large inconsistencies in the conductivity values reported in many papers, varying more than three orders of magnitude, are rather obvious, originated from non-equilibrium nature and slow recrystallization kinetics of semicrystalline state. (C) 2004 Elsevier Ltd. All rights reserved.