Metal-air batteries are the most compact and, potentially, the least expensive batteries available. They are also environmentally benign. The main disadvantage, however, is that electrical recharging of these batteries is very difficult and inefficient. Although many manufacturers offer refuelable units where the consumed metal is mechanically replaced and processed separately, not many developers offer an electrically rechargeable battery. Rechargeable metal air batteries that are under development have a life of only a few hundred cycles and an efficiency about 50%.
The anodes in these batteries are commonly available metals with high energy density like aluminum or zinc that release electrons when oxidized. The cathodes or air electrodes are often made of a porous carbon structure or a metal mesh covered with proper catalysts. The electrolytes are often a good OH- ion conductor such as KOH. The electrolyte may be in liquid form or a solid polymer membrane saturated with KOH.
While the high energy density and low cost of metal-air batteries may make them ideal for many primary battery applications, the electrical rechargeability feature of these batteries needs to be developed further before they can compete with other rechargeable battery technologies.
AER Energy Resources
Zoxy Energy Systems