Rechargeable Zinc-Air Batteries Could Threaten Li-ion’s Dominance (.PDF Download)

Current research on zinc-air batteries aims to transform this battery type from non-rechargeable to rechargeable. To describe how rechargeable zinc-air batteries work, we first have to look at their existing non-rechargeable counterparts, which are metal-air batteries activated by oxidizing zinc with oxygen from the air.

Non-rechargeable sizes range from very small button cells for hearing aids, to larger types used in cameras. You can’t use zinc-air batteries in a sealed battery holder because some air must come in. This battery requires oxygen in 1 liter of air for every ampere-hour of capacity.

During the discharge of a non-rechargeable zinc-air battery, a mass of zinc particles forms a porous anode, which is saturated with an electrolyte. Oxygen from the air reacts at the cathode and forms hydroxyl ions that migrate into the zinc paste and form zincate, releasing electrons to travel to the cathode. The zincate decays into zinc oxide and water that returns to the electrolyte. The water and hydroxyl from the anode are recycled at the cathode, so the water is not consumed. These reactions produce a theoretical 1.65 V, but this reduces to 1.35-1.4 V in practical cells.

It’s in the Air

Non-rechargeable zinc-air batteries have higher energy density and specific energy (and weight) ratio than other types of battery because atmospheric air is one of the battery reactants. The air is not packaged with the battery; therefore, a cell can use more zinc in the anode than a cell that must also contain, for example, manganese dioxide. This increases capacity for a given weight or volume. As a specific example, a zinc-air battery from one manufacturer with a 11.6 mm diameter and 5.4 mm height has a capacity of 620 mAh and weighs 1.9 g; various silver oxide and alkaline cells of the same size supply have a 150- to 200-mAh capacity and weigh 2.3-2.4 g.