MnO2/polyaniline composite was prepared by polymerization of aniline in alpha-MnO2 from the acid-treating precursor of delta-MnO2. XRD results showed that during acid treatment the precursor of delta-MnO2 was transformed into alpha-MnO2, and this in alpha-MnO2 polymorph kept unchanged in the subsequent processes, as intercalation and polymerization of aniline. Comparison of charge-discharge performances among the precursor, its acid-treated form and the final composite, showed that at current density of 200 mA . g(-1) the discharge capacity of the composite was 160.2 mA.g(-1), which is close to that of the acid-treated material (160.9 mA . g(-1)) but higher than that of the precursor (125.8 mA . g(-1)). More important, the MnO2/polyaniline composite showed a much better cyclic performance than the precursor and its acid-treated form
