Headline: A New Zinc-Air Battery Design Could Potentially Allow for Them to be Rechargeable

Author: Alex Bowser

Zinc-air batteries are known to be single-use batteries, though the benefits of being lightweight, inexpensive, and made of safe and sustainable materials still make them significant in the energy industry. However, researchers could potentially change this.

Researchers have invented a way that could allow for the reaction of zinc and oxygen that creates the energy for the battery to essentially be rechargeable. This can be made possible by simply altering the reaction and using slightly different materials to build the battery.

These zinc-air batteries use an alkaline-based electrolyte that requires a four-electron reduction of oxygen (O2) into water (H2O), but if this was made into a two-electron reduction by utilizing peroxide rather than alkaline, the chemistry makes the process reversible. 

What this means is the reduction is diminished by half, and making the electrolyte hydrophobic excluded from water at the surface. The ability to reverse the reaction and continue back and forth communication among the molecules is the process that allows for the battery to become rechargeable.

The zinc-air battery design is characterized by the two electrodes, more specifically a zinc anode and a porous cathode, separated by an electrolyte liquid. When oxygen enters the cathode, the water in the electrolyte reacts to it forming hydroxide, which in turn travels to the anode to react to the zinc creating energy that is released on the other side.

With the new rechargeable design, the electrolyte liquid is made up of water-repellant ions that stick to the cathode. This causes avoidance of the initial reaction happening at the surface of the cathode and allows for the reaction to essentially communicate throughout the battery rather than requiring it to be step by step.

Zinc ions from the anode are able to travel back and forth to and from the cathode and initiate the reaction of oxygen directly from the source. Because of the ability to traverse the battery freely, it can create a cycle of reactions.

As with any battery, however, the reaction becomes run down. As the battery is continuously used and recharged, the maximum charge begins to dwindle. With these rechargeable zinc-air designs, this is most prominent, as the lifetime of the battery’s capability to recharge from multiple charges is shorter than the average.

According to the lead researcher in the making of the rechargeable design, Wei Sun, he and his colleagues tested the lifetime and the charging cycle of the new battery cell they designed. They were able to recharge the battery 320 times until it no longer functioned, with roughly 160 hours, and they managed to cycle one battery for almost 1,600 hours total without the realistic factor of the density.

In addition, the researchers detected pressure changes during recharging sessions. They also tested various zinc forms such as zinc foil and zinc powder. When the foil was used as an electrode, over 80 percent of the zinc was used during discharge, but with the powder, the percentage used increased to 94 percent.

Though this may be a sign that the lithium-ion batteries are soon to be in trouble, we’re still a long way away from implementing this use. The biggest problem with the new zinc-air battery is that it takes upwards of 20 hours to recharge.

In addition, the researchers note that their methods in the chemistry they used could potentially work in other metals that could be cheaper to use, but the competition for lithium supply isn’t a major issue either.

It’s unclear how the design can evolve or how long it will be until we see it commercially, but with all the advantages and disadvantages it comes with, it’s safe to say that this initial design will bring more to the table.

Photo: cbc.ca/Melanie Ferrier