An attempt was made to clarify the transport mechanism of a promising energy storage system of Al–I2 batteries in both aqueous and non-aqueous solution for the first time. The different discharge features of the Al–I2 cells in the water and the acetonitrile solution were revealed. Ac impedance spectra indicated that the resistance of the Al/I2 cell in water solution reduced during discharging process gradually, while the resistance of the Al/I2 cell in the acetonitrile solution increased during discharging process. This could be due to the formation of a layer of amorphous AlI3 on the surface of aluminum anode, which was confirmed by the scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, high-resolution transmission electron microscopy and selected area electron diffraction measurements. An I− ion conductor, LiI-(3-hydroxypropionitrile)4 (LiI(HPN)4) with 15wt% SiO2/I2 cell was used as a solid electrolyte sandwiched between Al and I2 electrode to assemble the solid-state Al–I2 cell for further clarifying the transport mechanism. Our results demonstrated that the transport mechanism of Al–I2 cell in the water may be involved in both cation and anion transport mechanism, but in non-aqueous solution, it may be involved in cation transport mechanism.