Rechargeable Aluminum-Ion Batteries Based on an Open-Tunnel Framework

Rechargeable batteries based on an abundant metal such as aluminum with a three-electron transfer per atom are promising for large-scale electrochemical energy storage. Aluminum can be handled in air, thus offering superior safety, easy fabrication, and low cost. However, the development of Al-ion batteries has been challenging due to the difficulties in identifying suitable cathode materials. This study presents the use of a highly open framework Mo_2.5 + y VO_9 + z as a cathode for Al-ion batteries. The open-tunnel oxide allows a facile diffusion of the guest species and provides sufficient redox centers to help redistribute the charge within the local host lattice during the multivalent-ion insertion, thus leading to good rate capability with a specific capacity among the highest reported in the literature for Al-based batteries. This study also presents the use of Mo_2.5 + y VO_9 + z as a model host to develop a novel ultrafast technique for chemical insertion of Al ions into host structures. The microwave-assisted method employing diethylene glycol and aluminum diacetate (Al(OH)(C₂ H₃ O₂ )₂ ) can be performed in air in as little as 30 min, which is far superior to the traditional chemical insertion techniques involving moisture-sensitive organometallic reagents. The Al-inserted Al _x Mo_2.5 + y VO_9 + z obtained by the microwave-assisted chemical insertion can be used in Al-based rechargeable batteries.