One of the more promising battery technologies, particularly for portable computers, is zinc-air. These batteries are like other rechargeables except that, instead of two metal electrodes, they have only one. As their name implies, one electrode is made of zinc and the other, a virtual electrode, is composed of air.
Air electrodes function similar to heavy metal electrodes used in conventional batteries, such as nickel-cadmium, nickel-metal hydride, and lead-acid. In conventional batteries, however, all reactants are incorporated within the case, chemically bonded to heavy metals. Zinc-air batteries, on the other hand, extract oxygen molecules for chemical reactions directly from air. During charging, the oxygen is expelled. This “air breathing” nature translates into higher energy density in terms of both weight and volume