Scientists are working on rechargeable batteries based on zinc-air technology. Zinc-air batteries promise to be safer than li-ion, while costing about 50 percent less and offering three times as much energy density. More info at PhysOrg.
The new battery was developed in Trondheim in Norway by the SINTEF Group, the largest independent research institution in Scandinavia, and ReVolt was formed to market the device.
Zinc-air batteries need oxygen from the air to generate the current. They are safer than lithium-ion batteries because they do not contain volatile materials, and therefore do not catch fire. Non-rechargeable zinc-air batteries have been available for some time, but rechargeable versions have proved more difficult to develop.
The battery consists of an "air" electrode, an electrolyte, and a zinc electrode, all set in a casing that lets in air. When the battery is discharging the air electrode (with the help of catalysts) produces hydroxyl ions in the aqueous electrolyte. At the zinc electrode the hydroxyl ions oxidize the zinc, a process that releases electrons to form an electric current. During recharging the process is reversed, with oxygen being released at the air electrode.