The porous network structure of Li-ion battery electrodes has been first studied by combining the X-ray computed tomography (CT) technology and the three-dimensional image processing using medial axis. High resolution X-ray CT images of the electrodes were obtained at the synchrotron facility. Gallium injection technique was utilized to obtain a high contrast CT image for anode, so that the material and void are clearly separated in the further image processing. The tortuosity of voids in x-, y-, and z-directions was calculated after thinning process. The path of Li ion in electrodes is visualized and analyzed by this method. This analysis may accelerate the research and development of Li-ion battery electrode.