PEO based solid polymer electrolyte plasticized by dibutyl phthalate

Plasticized PEO based electrolyte membranes of various compositions, xPEO(1 - x)[LiCF3SO3/Dibutyl phthalate], where x varies from 0.17 to 0.84 were pr epared by solution casting. The concentration of salt (LiCF3SO3) in plastic izer, dibutyl phthalate (DBP) was fixed at 1 mol/kg. The thermal properties , electrical conductivity and vibrational spectra were studied. DSC reveale d the plasticizing effect of PEO for large amounts of plasticizer added DBP (50 wt%). Thermal events such as melting and glass transition were affecte d if the dissolution of components in solvent and drying of membrane was al tered in terms of duration. Complexation of salt to polymer was substantiat ed by the appearance of new bands not present in PEO/plasticized PEO and al so broadening of the C-O-C vibrations as the salt content increased. Room t emperature conductivity changed over 3 orders of magnitude, increasing from 7.1 X 10(-7) S cm(-1) for x = 0.84 to 6.0 x 10(-4) S cm(-1) for x = 0.33. This conductivity is much higher than in similar PEO-Lithium salt systems t hat are not plasticized. By correlating the trends in T-g and conductivity with composition, it appears that the enhancement can be attributed to, pri marily, an increase in carrier concentration. The plasticizer seems to play a catalytic role in dissociating the salt and increasing the carrier conce ntration. It is speculated from the present study as well as observations o f a similarly plasticised system, xPVC(1 - x)LiN(CF3SO2)(2)/DBP which was i nvestigated in detail, earlier, that the inclusion of the plasticizer, DBP in conventional polymer-Li salt changes the solvation mechanism. (C) 1998 P ublished by Elsevier Science B.V. All rights reserved.