In this work. the relationship between the nanoscale morphology and electrochemical performance of vanadium oxide and vanadium oxide/polyaniline nanofibers is analyzed. The nanofibers were prepared by reverse micelle method and their electrochemical performances were evaluated as potential cathode materials for secondary Li-ion batteries. Both types of samples were examined by electroacoustic impedance, ex situ X-ray diffraction, Raman and infrared spectroscopies, transmission and scanning electron microscopies to characterize their structure and morphology. It was found that vanadium oxide/polyaniline nanofibers show improved cycling behavior compared to the vanadium oxide ones. Nanofibers of vanadium oxide exhibit the largest capacity fading during cycling; on the other hand, the nanohybrid containing 30 mol% polyaniline exhibits a stable capacity of similar to 300 mAh g(-1). Scanning electron microscopy analyses indicated that the vanadium oxide nanofibers change the morphology after 10 charge/discharge, cycles while hybrid nanofibers retain the defined morphology after electrochemical cycling. The role of the polymeric component of the hybrid material seems to be the stabilization of the capacity due to a probable homogeneous distribution of the induced stress during cycling. (c) 2007 Elsevier Ltd. All rights reserved.