Ionic transport of Li+ in polymer films consisting of poly(3,4-ethylenedioxythiophene) and poly(4-styrenesulphonate)

A composite film consisting of poly(3,4-ethylenedioxythiophene) (PEDT) and poly(4-styrenesulphonate) (PSS), obtained by anodic polymerisation on a gold substrate electrode, has been characterised by electrochemical quartz microbalance (EQCM) measurements and impedance spectroscopy (IS), in a non-aqueous electrolyte containing LiClO4 in 1,2-dimethoxyethane (CH3OCH2CH2OCH3). The value of the capacitance was found to be over 25 F cm(-3) (5 mF cm(-2) for a 2 mum thick film), This confirms the possibility of the use of PEDT/PSS films in electrochemical capacitors. It has been established that lithium ions are sorbed and desorbed reversibly in a potential range corresponding to the oxidised form of the material (+0.4 to -0.2 V vs. Ag\AgCl\0.1 M KClaq). The ionic transport characterised by an effective diffusion coefficient (D-eff) was found to be the highest reported for electronically conducting polymers. D-eff decreases linearly from 6.5 x 10(-7) to 2.4 x 10(-7) cm(2) s(-1) in the potential range from +0.4 to -0.2 V vs. Ag\AgCl\0.1 M KClaq while the amount of lithium ions inserted in the film increases. The ionic conductivity equals 1.1 x 10(-5)-1.2 x 10(-5) Ohm (-1) cm(-1). The composite films are very stable. being polarised as a cathode in a lithium cell. The open circuit voltage of a tell with a lithium anode and a cathode made of the PEBT/PSS film is 3.37 V. (C) 2001 Elsevier Science B.V. AU rights reserved.