The redox reaction of 2,5-dimercapto-1,3,4-thiadiazole (DMcT) is slow at room temperature, but it can be accelerated when the electron transfer reaction is coupled with that of polyaniline (Pani). Films of polyaniline were electrosynthesized onto carbon fiber substrates by cyclic voltammetry from a 0.5 mol L-1 H2SO4/0.1 moll L-1 aniline aqueous solution; DMcT was incorporated into the films by two different procedures: A - previous adsorption on the carbon fiber substrate, and B - electropolymerization onto a Pani film from a 20 mmol L-1 DMcT solution in acetonitrile. The Pani(DMcT)/carbon fiber composites were tested as cathodes at 0.1 mA cm(-2) in a cell containing lithium as anode in a 0.5 mol L-1 LiClO4 solution in propylene carbonate, in a dry box under an argon atmosphere at 25 +/- 2 degrees C. Discharge capacity values of 159 mA h g(-1) (after 90 cycles) and 39 mA h g(-1) (after 50 cycles) were obtained for the composites prepared by procedures A and B, respectively. The high capacity value and the high electrochemical stability during the cycling indicate that there is a synergetic effect of Pani and DMcT in the composites prepared by procedure A. (c) 2005 Elsevier B.V. All rights reserved.