Self-tracking, solvent-free low-dimensional polymer electrolyte blends with lithium salts

Solvent-free polymer electrolyte blends of the amphiphilic polyethoxide (I) and the polytetrahydrofuran copolymer (II) with LiClO₄ or LiClO₄/LiBF₄ mixture have been prepared. In II -A- is either -CH₂- (IIC1) or -CH₂C(=CH₂)CH₂- (IID4), dc measurements using Li electrodes on the cells (Li|I/II-Li salt|Li) demonstrate a 'self-tracking' process over ca. 24 h during which time conductivities increase from ca. 10^-6 to 10^-3 S cm^-1 at 25 and 30°C. The dc results are supported by ac impedance measurements using indium tin oxide (ITO) electrodes in which the complexes undergo transitions at ca. 90°C to give a conductivity after cooling of 6 × 10^-4 S cm^-1 at 20°C with low temperature dependence. Structural analysis and molecular dynamics modelling indicate that the cations occupy unimpeded helices of I and anions are located in the interhelical spaces. Mechanisms of 'tracking' involving shear-induced orientation of polymer I by polymer II and the redistribution of ions between I and II following imposition of the field are proposed.