Review—On Order and Disorder in Polymer Electrolytes

This contribution presents an overview of more than three-decades-long studies of the structure and mechanism of ion conduction in polyethylene-oxide-based solid polymer electrolytes. Conductivity in polymer electrolytes has long been viewed as confined to the amorphous phase above the glass-transition temperature (Tg). Above Tg, polymer chain motion creates a dynamic, disordered environment that was thought to play a critical role in facilitating ion transport. Difficulty of finding the amorphous polymer with sufficient ionic conductivity has raised the fundamental question of whether polymer electrolytes are intrinsically inferior to other electrolytes in terms of their charge-transport capability. Recently, enhanced ionic conductivity has been detected in ordered (longitudinally stretched and cast under gradient magnetic field) polymer electrolytes, in crystalline ion–polyether 1:6 complexes and polymer-in-salt electrolytes. These results have opened a new trend in the search for ion transport in solid polymer electrolytes. The very latest publications present new hybrid- and block-co-polymers, a new class of functional materials (polymerized ionic liquids), and new promising approaches aimed at the development of polymer-based superionic conductors with rigid nanochannel architectures that enable rapid ion transport decoupled from segmental relaxation.