Effect of added salt species on the ionic conductivity of PEO/sulfonamide salt hybrids

Addition of low molecular weight lithium salt improved the ionic conductivity of poly(ethylene oxide) (PEO) with the average molecular weight of 1000 having sulfonamide lithium salt on both ends (PEO1900/SALi salt hybrid). These mixtures with the hybrid and a variety of lithium salts gave homogeneous viscous liquid. The DSC measurement revealed that the mixture was amorphous without the crystallization of PEO chains. Ionic conductivity of the mixture with hybrid and equimolar amount of LiClO4 was 1.6 x 10(-4) S cm(-1) at 50 degrees C which was 3.8 times higher than that of the hybrid without the salt. Slight addition of the salt, which has low lattice energy such as LiClO4, was effective for improvement of the ionic conductivity. Ionic conductivity of the mixture lowered by the increase of added salt concentration because of considerable increase of glass transition temperature (T-g). Among these, the mixture with lithium bis-(trifluoromethane sulfonyl)imide (LiTFSI) kept ionic conductivity high in a wide salt concentration without large elevation of the T-g. (C) 2000 Elsevier Science Ltd. All rights reserved.