Polymer solid electrolytes. Charge transport mechanisms

Solvent-free polymer electrolytes have become one of the most active areas of solid-state electrochemistry. The nature of the polymer/salt complex polymer electrolytes is discussed, and several important preparative and characterization schemes are described. The simplest understanding of the ionic mobility is in terms of the immobile solvent concept: ions move in a locally liquid-like solvent provided by the polymer chains, that are themselves immobile due to entanglements. The segmental motions of the polymer host, therefore, facilitate ion motion. This implies a Walden-like proportionality between ion diffusion and microviscosity, as has been observed. Both quasimacroscopic (free-volume) and kinetic (dynamic percolation) models are useful for understanding ion mobility in these materials. Conductivity is harder to understand, because the high salt concentrations give important ion-ion interaction effects, including ion pair formation. Classes, transport mechanisms and applications of polymer electrolytes are briefly described.