Aluminium ion batteries are considered to be a promising development for large-scale energy storage and conversion applications. In this research, a nanosphere-rod-like Co3O4 has been synthesized after the hydrothermal reaction and the subsequent heat treatment process, which is used for the cathode materials of aluminium ion batteries. The working mechanisms of the Co3O4 are deeply investigated. It is found that the electrochemical deposition and dissolution of aluminum occurs on the surface of pure aluminium anode, and the Al3+ cations are intercalated and de-intercalated in the cathode materials during the discharge and charge processes. The battery exhibits a high discharge specific capacity of 490 mAh g−1 at the first cycle, with the current density of 50 mA g−1. Furthermore, the discharge capacity still maintains a high level of 122.1 mAh g−1 after 100 cycles at the current density of 200 mA g−1, indicating a good cycle performance. Therefore, the nanosphere-rod-like Co3O4 as the cathode for aluminium ion batteries has a promising potential.