Zinc-air batteries have many things in common. They are lightweight, compact and made with more sustainable and less flammable materials than other batteries. But they are usually not rechargeable.
A new battery design could change that. By tweaking the building materials, the researchers created a prototype zinc-air battery that could be recharged hundreds of times. These long-lasting devices, described in the January 1 issue of the journal Science, could one day power electric cars or other electronic devices.
Zinc-air batteries are one of many potential next-generation batteries that could hold more power while being cheaper and safer than existing devices (SN: 1/9/17). Each zinc-air battery cell contains two electrodes – a zinc anode and a porous cathode – separated by a liquid called an electrolyte. In standard air and zinc cells, the electrolyte is a high pH substance, which contains ingredients such as potassium hydroxide. Oxygen from the air enters the cathode, where the gas reacts with the electrolyte water to form hydroxide. The hydroxide formed on the surface of the cathode travels to the anode and reacts with the zinc to release energy that feeds other devices.
“The problem is that 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 these problems, Sun and his colleagues built a zinc-air battery using a new electrolyte containing water-repellent ions. These ions adhere to the cathode, preventing the H2O from the electrolyte from reacting with the oxygen entering the cathode surface. As a result, the zinc ions in the anode can travel to the cathode and react directly with the oxygen in the air. This relatively simple reaction is easy to run backwards to recharge the battery.
What’s more, the new electrolyte does not degrade the battery electrodes, which helps it last longer. In lab experiments, Sun and colleagues were able to drain and recharge a new zinc-air battery cell 320 times in 160 hours.