Coming: Rechargeable zinc-air cells

The Swiss company ReVolt plans to release a new kind of zinc-air battery next year, initially for use in hearing aids, later for cell phones. Eventually much larger batteries are planned for electric vehicles.

Zinc-air batteries need oxygen from the air to generate current. They are safer than lithium-ion batteries because they do not contain volatile materials, and thus 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 ReVolt 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.

Previous rechargeable zinc-air batteries had an air electrolyte that became deactivated and the reduction and oxidation reactions slowed or stopped after a few discharge/recharge cycles. The new battery uses gelling and binding agents to control the zinc electrode shape, and controls the humidity inside the battery. It uses new catalysts that improve both the reduction and production of oxygen during discharge/recharge cycles.

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