A Prototype Rechargeable Aluminum Battery

Although Lithium-ion battery technologies have made significant positive impact on portable electronics and electric vehicle industries, the feasibility of wide deployment of lithium-based batteries for land-based renewable energy storage and grid applications may be questionable due to the limited lithium resource, the resource geographic distribution, and the cost of lithium mining and recycling. Therefore, alternative rechargeable battery technologies based on abundant elements need to be developed for sustainable energy storage. Among the potential candidates, aluminum (Al) may be the ultimate choice as the anode material: Al is not only the most abundant metal in earth’s crust, but also has attractive capacity due to its trivalency. Al has the second highest specific capacity of 2980 mA h g^-1 (Li has 4634 mA h g^-1) and the highest capacity density of 8046 mA h cm^-3 (Li has 2456 mA h cm^-3) among all metal anodes. To date, there were only scarce investigations on rechargeable Al batteries with little success.  For the first time, we demonstrate a new prototype rechargeable Al battery comprised of Chevrel phase molybdenum sulfide (Mo₆S₈) as the intercalation-type cathode, Al metal as the anode, and a mixture of AlCl₃ and 1-butyl-3-methyimidazolium chloride (AlCl₃-[BMIm]Cl) as the electrolyte. The Mo₆S₈ cathode shows unambiguous electrochemical activity for reversible Al intercalation and extraction and good cycle stability. The chronopotentiometric plateaus in Al-Mo₆S₈ charge-discharge curves indicate phase-transition type of electrochemical reactions. In addition to the electrochemical analysis, XRD studies provide the crystallographic information of the Al intercalated Mo₆S₈. We conclude that the theoretical chemical formula of fully Al intercalated Mo₆S₈ is Al₂Mo₆S₈ with Al occupying two different sites in the Mo₆S₈ crystal lattice. The theoretical material-level specific energy of the Al-Mo₆S₈ battery is approximately 90 Wh kg^-1 (assuming 0.5 V nominal voltage), which makes this new rechargeable battery technology an attractive alternative for large-scale sustainable energy storage.