Understanding the Failure Mechanism of Rechargeable Aluminum Batteries: Metal Anode Perspective Through X‐Ray Tomography

Rechargeable aluminum batteries (AlBs), which represent cost‐effective energy‐storage devices due to the abundance of natural aluminum resources, have emerged as promising candidates for the next generation of rechargeable batteries. Although the electrochemical deposition of aluminum in ionic liquids (ILs) is well investigated for aluminum refining, the reversible electrochemical deposition/dissolution behavior of aluminum ions is not trivial. More specifically, the dendrite growth issue, which is common in Li metal anodes, is scarcer or vague. Herein, the electrochemical stability of the aluminum metal anode in IL electrolytes is investigated and the failure mechanism is discussed. It is confirmed that the inorganic anion of ILs mainly affects the electrochemical stability, whereas the organic cation influences the aluminum metal degradation. X‐ray computed tomography results further identify deterioration of the surface morphology of the aluminum metal. The formation of “dead aluminum” is further confirmed, which indeed causes cell failure with repeated cycles. Finally, using the predeposited aluminum graphene paper as an alternative anode candidate for AlBs is further demonstrated. With imidazolium‐based ionic liquid electrolytes, cation and anion species have different aspects toward the failure mechanism of aluminum batteries (AlBs). More critically, aluminum metal anodes suffer from “dead aluminum” formation, resulting in cell failure. Cathode‐free AlBs present Al‐predeposited graphene paper as a promising anode to avoid cell failure.