Lithium ion and electronic conductivity in 3-(oligoethylene oxide)thiophene comb-like polymers

The Li-ion and electronic conductivities of a series of p-doped poly(thiophene)s with oligo-ethylene oxide side chains have been determined at room temperature as functions of side-chain length and concentration of LiOTf dissolved in the polymers in order to assess their utility as binders in Li-ion batteries. The lithium triflate concentration was varied from 0.23. to 2.26mmol LiOTf/g -C2H4O- (100 O:Li to 10 O:Li), and the concentration of dissociated Li+ was determined from the IR spectra of the polymer solutions. The greatest ionic conductivity, 2 x 10(-4) S cm(-1), was attained with intermediate concentrations of added salt that corresponded with the greatest degree of LiOTf dissociation. Li-ion mobilities of 5 x 10(-7) cm(2) (VS)(-1) were measured for poly(thiophene)s (PT) with short oligo(ethylene oxide) side-chains (E-n), PE2T and PE3T, whereas the polymers with longer side chains, PE7T and PE15T, had Li-ion mobilities about an order of magnitude greater, 5 x 10(-6) cm(2) (Vs)(-1). The electronic conductivity of the polymers heavily doped with NOBF4 was near 0.1 S cm(-1) for PE2T and PE3T, but was orders of magnitude smaller for the polymers with longer side-chains. Addition of LiOTf caused the electronic conductivity of PE2T and PE3T to drop to that of the longer chain polymers whose conductivities were insensitive to the LiOTf concentration. (c) 2005 Elsevier B.V. All rights reserved.