Aluminum-ion batteries (AIBs) have been regarded as a promising candidate for large-scale stationary energy storage applications based on their low cost, good safety and high volumetric capacity. However, the lack of suitable cathode materials with highly reversible aluminum storage has hindered their practical use. Here, we demonstrate a highly reversible AIB using porous Co3S4 microspheres as the cathode material. The microstructure gives Co3S4 a superior electrochemical performance to most other cathode materials for AIBs reported so far. It is further shown that the cell undergoes Al3+ intercalation/deintercalation with Co3+/Co2+ as a redox couple in the cathode, and electrochemical stripping/plating of metallic aluminum in the anode. We also found that the diffusion of Al3+ in the host Co3S4 is the key kinetic step that limits the discharge/charge current density. This work is a step forward in the development of a low-cost cathode material for high-performance AIBs and contributes to a better understanding of AIB chemistry.