The relation between ion transport and relaxation dynamics in polymers

Li-ion batteries are important as power sources for portable devices (e.g. laptops and mobile phones) and their use is predicted to grow substantially in the near future. Unfortunately, we lack safe, easy-to-process (low-cost), ideally mechanically flexible batteries. A possibility is solvent-free polymeric electrolytes. However, a key challenge is to decouple ionic transport from segmental relaxation and thus achieve good transport properties and mechanical rigidity. Previous work has varied the degree of decoupling in polymers by altering their properties (such as fragility, glass-transition temperature, chain flexibility). However, there is no clear understanding of the mechanisms behind this decoupling phenomenon. We here present work to help understand the decoupling between ionic transport and polymer dynamics. We will discuss experimental work on homo- and co-polymers where we have studied structure, relaxation dynamics and ion transport using dielectric spectroscopy, DSC, rheology, x-ray scattering, NMR and AFM. Results will be presented in the context of different models and ideas suggested in the literature to address the observed decoupling.