The effect of pore structure on anomalous behaviour of the lithium intercalation into porous V2O5 film electrode has been investigated in terms of fractal geometry by employing ac-impedance spectroscopy combined with N-2 gas adsorption method and atomic force microscopy (AFM). For this purpose, porous V2O5 film electrodes with different pore structures were prepared by the polymer surfactant templating method. Front the analysis of N-2 gas adsorption isotherms and the triangulation analysis of AFM images, it was found that porous V2O5 surfaces exhibited self-similar scaling properties with different fractal dimensions depending upon amount of the polymer surfactant in solution and the spatial cut-off ranges. All the ac-impedance spectra measured on porous V2O5 film electrodes showed the non-ideal behaviour of the charge-transfer reaction and the diffusion reaction, which resulted from the interfacial capacitance dispersion and the frequency dispersion of the diffusion impedance, respectively. From the comparison between the surface fractal dimensions by using N-2 gas adsorption method and AFM, and the analysis of ac-impedance spectra by employing a constant phase element (CPE), it is experimentally confirmed that the lithium intercalation into porous V2O5 film electrode is crucially influenced by the pore surface irregularity and the film surface irregularity. (c) 2005 Elsevier Ltd. All rights reserved.