Rechargeable zinc-air batteries zero in on lithium
Zinc-air batteries are an enticing prospect thanks to their high energy density and the fact they're made with some of the most common materials on Earth. Unfortunately, those advantages are countered by how difficult it is to recharge these cells. Now, a team at the University of Sydney has created new catalysts out of abundant elements that could see rechargeable zinc-air batteries vying with lithium-ion batteries in mobile devices.
The chemical reaction that drives zinc-air batteries to produce electricity comes from the air around the cell. They essentially breathe in oxygen that interacts with a carbon cathode to produce hydroxyl, which in turn interacts with a zinc anode to generate an electric current. Using air as a reactant allows the battery to cram in more zinc, increasing the energy density and making the battery fairly lightweight and safe.
But the problem is that once the zinc anode has been oxidized, it isn't much use. These batteries can be mechanically "recharged" by replacing the zinc component completely, or by using electrocatalysts made from rare-earth minerals that reduce oxygen while discharging the battery, and generate it while recharging.
"Up until now, rechargeable zinc-air batteries have been made with expensive precious metal catalysts, such as platinum and iridium oxide," says Yuan Chen, lead author of the study. "In contrast, our method produces a family of new high-performance and low-cost catalysts."
To create their new electrocatalysts, the researchers made metal oxides out of common elements like iron, cobalt and nickel. Their production method ups the efficiency by very carefully controlling the composition, size and crystallinity of these metal oxides, and the end result can be used to build more easily-rechargeable zinc-air batteries.
To test their new batteries, the team charged and discharged them for 60 cycles of 120 hours, and found that the cells lost less than 10 percent of their efficacy. That means they aren't quite as effective yet as their lithium-air cousins, but they should be cheaper and easier to produce.
The research was published in the journal Advanced Materials.
Source: University of Sydney