Segmental relaxation and ion transport in polymer electrolyte films by dielectric spectroscopy

Abstract

The glass transition and dielectric relaxation processes of polyethylene oxide (PEO) based polymer salt complexes (PSCs) have been investigated using broadband dielectric spectroscopy, in order to better understand the role of segmental relaxation dynamics in ion transport process. Neat PEO and PSCs consisting of PEO, LiClO4 or LiCF3SO3 were synthesized with and without nano-particulate TiO2 by solution casting method. The dielectric loss (ε″) spectrum showed two segmental relaxations for both neat PEO and PSCs, and these are assigned as fast and slow segmental relaxation modes. The slow relaxation is associated with cation coordinated segmental motions, where as, the fast relaxation could be due to the motion of PEO chain segments. The strength and location of slow relaxation frequency showed a drastic change in PSCs when compared to neat PEO, and found to depend on the nature of anions in the salts. Furthermore, the temperature dependence of ac conductivity changes seemed to corroborate well with the observed slow relaxation behavior, suggesting that the polymer segmental dynamics play a crucial role in controlling ion transport process in polymer electrolyte systems.