A redesign for zinc-air batteries could make them rechargeable

Zinc-air batteries have a lot going for them. They’re lightweight, compact and made of more sustainable, less flammable materials than other batteries. But they’re usually not rechargeable.

A new battery design could change that. By tweaking the building materials, researchers created a prototype of a zinc-air battery that could be recharged hundreds of times. Such long-lasting devices, described in the Jan. 1 Science, could one day power electric cars or other electronics.

Zinc-air batteries are one of many potential next-generation batteries that could hold more energy while being cheaper and safer than existing devices (SN: 1/9/17). Every zinc-air battery cell contains two electrodes — a zinc anode and a porous cathode — separated by a liquid called an electrolyte. In standard zinc-air cells, the electrolyte is a high-pH substance, containing ingredients like potassium hydroxide. Oxygen from the air enters the cathode, where the gas reacts with water from the electrolyte to form hydroxide. Hydroxide formed at the cathode surface travels to the anode and reacts with zinc to release energy that powers other devices.

“The problem is, this reaction is not very reversible,” says Wei Sun, a materials scientist at the University of Münster in Germany. And that makes it hard to recharge the battery. The caustic electrolyte in conventional zinc-air batteries can also degrade the cathode and anode.

To solve those problems, Sun and colleagues built a zinc-air battery using a new electrolyte that contains water-repellant ions. Those ions stick to the cathode, preventing H2O from the electrolyte from reacting with incoming oxygen at the cathode surface. As a result, zinc ions from the anode can travel to the cathode and react directly with oxygen from the air. This relatively simple reaction is easy to run backward to recharge the battery.

What’s more, the new electrolyte doesn’t degrade the battery’s electrodes, which helps the battery last longer. In lab experiments, Sun and colleagues were able to drain and recharge a new zinc-air battery cell 320 times over 160 hours.

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