A polymer composite cathode prepared from polyaniline and 2,5-dimercapto-1,3,4-thiadiazole shows high gravimetric energy density when it is coupled with a lithium anode. However, charging and discharging currents should be 0.05 mA/cm(2) or less, otherwise the cycle life is shortened. Addition of a polypyrrole derivative, poly(3-butylcarboxylate-4-methylpyrrole) to the composite cathode enabled rapid charging at 0.2 mA/cm(2) without undue deterioration of the energy density, but it was not effective for rapid discharging, This effect of the polypyrrole derivative may be ascribable to the electrical conductivity in its oxidized state.