metalair

Metalair refers to a family of energy storage devices in which a metal serves as the anode and oxygen from ambient air acts as the cathode oxidant. Common chemistries in the metalair family include zinc-air, aluminum-air, and lithium-air. These systems rely on the oxidation of the metal at the anode and the reduction of oxygen at a porous air cathode, with reaction products such as oxides or hydroxides forming during discharge.

Zinc-air cells are the most commercially deployed within the metalair category, particularly in primary (non-rechargeable) batteries used in hearing aids and some remote devices. Aluminum-air and lithium-air configurations have attracted significant research attention for rechargeable or semi-rechargeable (secondary) applications, especially in contexts that require high theoretical energy density.

Advantages of metalair systems include the potential for high energy density and the use of abundant, inexpensive metals. The open-air cathode design can also reduce the weight of stored energy, which is attractive for portable and transportation applications. However, several challenges limit widespread adoption: many metalair chemistries struggle with reversible cycling and low round-trip efficiency; maintaining stable air cathodes is difficult due to catalyst degradation, flooding, carbon dioxide, and moisture management; and charging can provoke unwanted side reactions, including hydrogen evolution in some designs.

Applications and status vary by chemistry. Zinc-air is established in disposable sensors and hearing aids; rechargeable metalair systems are primarily in the research and development phase, with ongoing work aimed at improving cycle life, safety, and cost. The field remains promising for niche long-range or lightweight energy storage if technical hurdles are overcome.