Polymer electrolytes

Polymer electrolytes are ionically conducting solid phases formed by the dissolution of salts in ion-coordinating macromolecules. Such materials may be readily fabricated as films using continuous production plant and are being considered as replacements for conventional low-molecular-weight liquid-based electrolytes for practical electrochemical devices such as power sources, variable-transmission windows and displays. The mechanism for ionic transport in polymer electrolytes is novel and quite distinct from the processes occurring in liquid solutions, molten salts or crystalline solid electrolytes. Ion mobility is associated with local structural relaxations of the polymer, although the relationship is not simple. For certain charge carriers local matrix motion simply provides time-dependent pathways or opportunities for ions to move between suitable low-energy sites; for others a mechanism involving short-range transport of ions temporarily attached to the polymer chain is important. For cations, lability of the ion–solvent bond is a necessary condition for long-range transport.