Aluminum-air batteries: A review of alloys, electrolytes and design

High theoretical energy densities of metal battery anode materials have motivated research in this area for several decades. Aluminum in an Al-air battery (AAB) is attractive due to its light weight, wide availability at low cost, and safety. Electrochemical equivalence of aluminum allows for higher charge transfer per ion compared to lithium and other monovalent ions. However, significant challenges have impeded progress towards commercialization, including formation of an aluminum hydroxide surface barrier, high aluminum corrosion rate, and self-discharge susceptibility. Addition of alloying elements is a widely used technique for mitigating these problems in aqueous electrolytes. A number of alloying elements have been evaluated, with typical characteristics such as higher nobility than aluminum, and high overpotential for hydrogen evolution. Over time, a large number of studies have examined alloys across a broad landscape of components and composition in aqueous and ionic liquid electrolytes. This manuscript first takes a broader look at metal-air battery performance before focusing on a summary of data and electrochemical performance for aluminum and aluminum alloys of indium, tin, and/or gallium, and surveys proposed mechanisms driving surface chemistry in alkaline electrolytes on aluminum alloy anodes comprising these materials. AAB performance of ionic liquid and solid-state electrolytes with aluminum anodes is also considered, as results to date support the idea that these designs have the potential to minimize corrosion and enable secondary capability for applications requiring rechargeability.