Stable Performance of Aluminum‐Metal Battery by Incorporating Lithium‐Ion Chemistry

Based on the recent discovery of the ionic liquid involving the AlCl4−-Al2Cl7− redox couple as an electrolyte, aluminum (Al) rechargeable batteries have received revamped interest. However, the corrosive nature of the chloride ion and Al2Cl7− makes it challenging to find suitable current collectors and cathode materials. Here, we screen various metals and carbon materials as current collectors, and indeed find that none of the metals commonly used for battery current collectors is stable against corrosion from the electrolyte. Only pyrolytic graphite is stable, but exhibits undesired AlCl4− intercalation at 1.7 V vs. Al/Al3+. The addition of lithium chloride (LiCl) salt to the electrolyte not only eliminates AlCl4− intercalation through Li−AlCl4− coordination, but also extends the stable voltage window to 2.3 V vs. Al/Al3+. Moreover, the incorporation of Li ions allows us to engage the established LiFePO4 olivine cathode in Li-ion batteries. This Al−Li hybrid cell exhibits an operation voltage of 1.3 V with robust cyclability (83.4 % retention after 400 cycles) and minimal self-discharge. This series of results suggest that proper employment of Li-ion chemistry can improve the electrochemical performance and safety of Al rechargeable batteries.